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This article was downloaded by: [Universitat Politècnica de València]On: 24 October 2014, At: 17:26Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Liquid Chromatography &Related TechnologiesPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/ljlc20
ON-LINE PRECONCENTRATION INCAPILLARY ELECTROPHORESIS FORANALYSIS OF AGROCHEMICAL RESIDUESRou Fang a , Ling-Xiao Yi a , Yu-Xiu Shao a , Li Zhang a & Guan-HuaChen aa College of Food and Bioengineering , Jiangsu University ,Zhenjiang , ChinaAccepted author version posted online: 20 Aug 2013.Publishedonline: 11 Mar 2014.
To cite this article: Rou Fang , Ling-Xiao Yi , Yu-Xiu Shao , Li Zhang & Guan-Hua Chen (2014)ON-LINE PRECONCENTRATION IN CAPILLARY ELECTROPHORESIS FOR ANALYSIS OF AGROCHEMICALRESIDUES, Journal of Liquid Chromatography & Related Technologies, 37:10, 1465-1497, DOI:10.1080/10826076.2013.794740
To link to this article: http://dx.doi.org/10.1080/10826076.2013.794740
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ON-LINE PRECONCENTRATION IN CAPILLARY ELECTROPHORESISFOR ANALYSIS OF AGROCHEMICAL RESIDUES
Rou Fang, Ling-Xiao Yi, Yu-Xiu Shao, Li Zhang, and Guan-Hua Chen
College of Food and Bioengineering, Jiangsu University, Zhenjiang, China
& Capillary electrophoresis (CE) has been recognized as a highly attractive separation techniquefor determining agrochemical residues in agricultural produces and environmental matrices due toits extremely high column efficiency, rapid analysis, and less reagent consumption. However,a small sample size and a short optical path length make the low concentration samples detectedwith an ultraviolet (UV) detector difficult or even impossible without sample preconcentration.The on-line concentrating techniques promise to extremely increase sample size without the changesof CE instrument and make the detection of agrochemical residues possible by CE. This reviewdescribes these on-line preconcentration techniques and comments their applications in thedetermination of agrochemical residues.
Keywords agrochemical residues, capillary electrophoresis, on-line preconcentration,on-line solid phase extraction, stacking, sweeping
INTRODUCTION
Agrochemical is a generic term used to describe a large number ofwidely differing biological, inorganic, and organic compounds, includingpositional, geometric, and optical isomers, employed in the control, andprevention of plant diseases and insect pests.[1] Agrochemicals oftencontaminate the environment, causing serious hazards to public health,through incorporation of residues in waters, soils, and crops. Therefore,rapid and reliable detection of agrochemical residues are required.Furthermore, the applied methods should be able to simultaneouslydetermine multiple agrochemicals with good reproducibility, high recovery,and low limit of detection (LOD).[2] Nowadays, the most popular techni-ques for the determination of agrochemicals in real sample remain to begas chromatography (GC) and high-performance liquid chromatography
Address correspondence to Guan-Hua Chen, College of Food and Bioengineering, JiangsuUniversity, 301 Xuefu Road, Zhenjiang 212013, China. E-mail: [email protected]
Journal of Liquid Chromatography & Related Technologies, 37:1465–1497, 2014Copyright # Taylor & Francis Group, LLCISSN: 1082-6076 print/1520-572X onlineDOI: 10.1080/10826076.2013.794740
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(HPLC). As GC has high sensitivity and selectivity, it is frequently employedto analyze the agrochemical residues. However, some agrochemicals thathave thermal instability, high polar and low-volatility cannot be determinedor determined directly by GC. They are necessarily prepared as stablederivatives, and then are indirectly determined by GC. Compared with GC,HPLC can be applied to determine virtually any organic solute regardlessof its volatility or thermal stability. The disadvantage of HPLC is insufficientseparation efficiency, large amounts of expensive and toxic organic solventused as the mobile phase. In recent years, CE has become a mature tech-nique to the analysis of great variety of the targets just like HPLC. The pro-spects for CE in agrochemical analysis are promising, because of theadvantages such as high separation efficiency, minimal sample requirements,and few need to be organic solvents, which makes CE an environmentallyfriendly separation technique.[3] However, the use of CE for analyzingagrochemical residues suffers from low concentration sensitivity with UVdetection, due to the small injection volumes and a narrow optical pathlength. This then limits the application of CE for agrochemical residues.
To improve the concentration sensitivity in CE, several high sensitivitydetectors have been used, such as chemiluminescence, laser-induced fluor-escence (LIF), and electrochemical detectors. LIF and chemiluminescencedetectors can increase sensitivity more than 1000-fold than that of theconventional absorbance detector, while electrochemical detectors do notprovide high sensitivity but their detection volume could be as low as tensof fL.[4] However, the price of most high sensitivity detectors is expensivefor a common laboratory; what is more, LIF detection is not widelyapplicable to environmental samples because only a few compounds havenative fluorescence and most analytes need to be derivatized with a suitablefluorescent tag. Another solution to the problem is to apply off-line or on-linesample concentrating methods. The concentrating efficiency of off-linetechnique is rather limited up to 100-folds in these sample pretreatmentsbecause of difficult handlings of large sample volumes.[4] While on-linesample preconcentration have been employed by the injection of a largevolume of sample in the capillary without modification of the instrument.Therefore, on-line sample preconcentration is a useful technique foragrochemical residue analysis in CE. Numerous preconcentration techniquesbased on electrophoretic principles, chromatographic principles, or theircombinations have been proposed recently. Both charged and neutralanalytes can be concentrated.[5–7]
On-line sample preconcentration in the field of agrochemical residueanalysis by CE is a topic that attracted much attention last 10 yearsand several research articles were published even after the year 2000.[8,9]
Thus far, however, most of review articles are published to describe on-linesample preconcentration techniques with an emphasis on the mechanism
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and advantages and disadvantages of each technique, only a few of themrefer to the application of these techniques in agrochemical residues. Somereview articles described the CE techniques for the determination ofagrochemical residues, but they mainly involved the off-line sample precon-centration techniques, the on-line techniques only were briefly introduced.As far as we know, until now, no review article has only focused on the use ofon-line sample preconcentration techniques in agrochemical residueanalysis. Therefore, the purpose of this review is to offer a description ofthe present status of agrochemical residue analysis by means of the on-linesample concentrating techniques. The fundamentals and applications ofon-line sample concentrating in CE are both considered.
ON-LINE SAMPLE STACKING TECHNIQUES
The principle of sample stacking method is mainly based on differencebetween the conductivity of the sample solution and that of backgroundsolution (BGS). It was first conceived for ionic solutes, and later extendedto the separation of neutral analytes in CE as described by Z. Liu et al. in1994.[10]
According to the principle of stacking techniques, many stackingmodes have been developed for concentrating analytes from differentsamples, such as normal stacking mode (NSM),[11] large-volume samplestacking (LVSS),[12] reversed electrode polarity stacking mode (REPSM),[13]
stacking with reverse migrating micelles (SRMM),[14] stacking usingreverse migrating micelles and water plug (SRW),[15] field-enhanced sampleinjection (FESI), field-enhanced sample injection with reverse migratingmicelles (FESI-RMM),[16] and so forth. Some sample stacking modalitieshave also been widely used to improve sensitivity in the analysis of agro-chemical residues.
Stacking in CZE
Normal Stacking ModeNSM is the simplest among sample stacking modes. The sample dissolved
in low electrical conductivity buffer is hydrodynamically introduced as a longplug and then a voltage is applied. The focusing mechanism of NSM isprimarily based on the abrupt change in electrophoretic velocity betweenthe low conductivity matrix and the BGS. A limitation of NSM is that the opti-mum sample plug length without loss of separation efficiency or resolution isshort.[17] This is because of the broadening of the stacked zones caused bythe mixing of low-conductivity and high-conductivity areas in the concentrat-ing boundary, and the laminar flow generated inside the capillary that results
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from the difference of local and bulk electro-osmotic mobilities.[2] Obviouslydecreasing in resolution and widening of peak wide occurs with increasing inthe injection of sample solution. Therefore, in this technique, the injectionvolume of sample is limited, the analytes are concentrated about 10-fold andoften does not exceed about 5-fold.[8,18–22]
Large Volume Sample StackingLVSS is a very promising technique to overcome the limitation of
injection volumes. The sample size in LVSS is larger than the optimumfound in NSM. To preserve separation efficiency from decrease, the samplematrix must be pushed out from the capillary. Pumping is performed withexternal pressure or with EOF. The direction of pumping is always oppositeto that of the electrophoretic movement of charged analytes and its velocityis also lower than the electrophoretic velocity of the charged solutes.[23]
A limitation in LVSS is that only positive or negative analytes can beeffectively concentrated at one time. LVSS has demonstrated an enhance-ment of more than 100-fold in concentration sensitivity,[24] improvingLOD from two orders of magnitude. LVSS includes two modes, with orwithout polarity switching.
LVSS with Polarity Switching. In this LVSS mode, polarity switching isused to control the direction of EOF. For the case of anions, the steps donein this mode can be found in Figure 1. A large sample plug with lowconductivity is hydrodynamically injected into a capillary and a negativepotential is applied to the inlet of capillary. The large solvent plugaccompanied with cations and neutral substances is pushed out from thecapillary by the EOF, whereas the negative species are stacked up at theboundary between the sample zone and the BGS. Once the major part ofthe low conductivity zone has been pushed out from the capillary, whichthe observed current reached 90–99% of the actual current (currentobtained when the capillary is filled with BGS only), the polarity at the inletof capillary is switched.[25–27] Undoubtedly, anionic=cationic species can beconcentrated in LVSS with polarity switching mode. However, nonrepro-ducible results can be led to if the current is not monitored properly duringthe backout step. Additionally, it cannot be performed in all commercialCE instruments.
LVSS Without Polarity Switching. Adding the EOF modifier to buffer[28]
or using a low pH buffer,[29,30] LVSS without polarity switching cansuppress the EOF, and get rid of polarity switching step. The detectionsensitivity is enhanced in the range of 100–300-fold. The steps performedin this mode are shown in Figure 2, with anions that are concentrated by
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FIGURE 2 LVSS without polarity switching mode to anions. A) a sample prepared in a low conductivitymatrix is injected into the capillary conditioned with a BGS; B) a negative voltage is applied to focuszones and remove sample matrix; and C) the focused zones are separated.
FIGURE 1 LVSS with polarity switching mode to anions. A) a large sample plug with low conductivityis hydrodynamically injected into a capillary; B) a negative potential is applied at the inlet of capillary;C) the anionic analytes are stacked up at the boundary between the sample zone and the BGSand most of the sample matrix are removed; and D) the polarity is switched when the current reaches90%–99% of its normal value; and E) the following separation occurs by CZE mode.
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using a low pH buffer. Because the suppressed EOF is lower than theelectrophoretic velocity of the analytes, the sample matrix is pumped outfrom the inlet of the capillary under reverse voltage. After that, the stackedanions migrate toward the detector end of the capillary and are separatedwithout polarity switching. The electrophoretic mobility of the analyte ionsshould be opposite to and greater than that of EOF in this mode.[31] Forcations, in addition to reducing the velocity of EOF, its direction shouldalso be reversed. A reduced and reversed EOF can be achieved by usinga low pH buffer containing a low concentration of cationic surfactant orusing specially coated capillaries.[32]
Field-Enhanced Sample Injection
In FESI, the sample that has lower conductivity than the BGS is electro-kinetically injected. Then, the ions are electrophoretically migrated intoBGS and dramatically slowed down at the boundary between sample andBGS.[33] In this case, only charged analytes or neutral analytes dissolvedin micellar solutions can be electrokinetically injected and concentratedby applying positive or negative voltage depending on the charge of theanalyte. The injected sample size can be much larger in FESI than in LVSSbut the injected analytes are biased by their electrophoretic mobility. Itshould be noted that the injected sample size is not proportional to theinjection time because the overlong injection time can deplete the analytesin the sample solution.[4]
The neutral analytes can be apparently charged when they are incor-porated with the micelles. However, their enrichment multiples dependon their retention factors.[34] The weaker the interaction between analyteand micelle is, the lower the enrichment multiple of the analyte is, becauseweak interaction results in low apparent electrophoretic mobility producedfrom the low apparent charge of analyte.
Stacking in MEKC
Reversed Electrode Polarity Stacking ModeREPSM is an on-line preconcentration strategy that involves polarity
reversal. In this technique, the capillary is filled with a micellar BGS andthe analytes prepared in low-conductivity matrix are injected for a longperiod of time by pressure mode. Then, a negative voltage is applied, theEOF moves toward the inlet of capillary. At this moment, the anionic ana-lytes and neutral analytes, which can be absorbed on the charged micelles,are respectively stacked at both boundaries of sample plug and movetoward the detector. The electrophoretic velocity of micelles at the front
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boundary of sample plug is slower than that of EOF but the electrophoreticvelocity of micelles at the back boundary of sample plug is faster than thatof EOF because the field strength is lower in BGS than in sample plug.Finally, the both boundaries meet each other, and the sample matrix ispumped out from the capillary by EOF. The dispersive effect can be mini-mized in REPSM through removing the sample matrix by applying negativevoltage. When the electrophoretic current reaches approximately 95%–99% of its original value, the polarity is switched to positive. However, thismethod involves a delicate operation to monitor the current carefully andleads to poor reproducibility if the current is not monitored well.[35]
Stacking with Reverse Migrating Micelles ModeInstead switching the electrode polarity in REPSM, an acidic micellar
BGS can be used to reduce the EOF.[36] The sample is dissolved in purifiedwater or in low conductivity matrix. The sample solutions are introducedinto capillary from the inlet at cathode and then separation is performedunder the reverse voltage with negative polarity at inlet. It is the methodthat is so-called SRMM. Since the negative polarity is applied at the inlet,the EOF slowly pushes out the sample matrix from the capillary, and separ-ating and stacking are simultaneously carried out. Compared with REPSM,a better reproducibility is achieved in SRMM without a polarity-switchingstep. In SRMM, the more hydrophobic analytes are, the higher theirenrichment factors are and the shorter their migration times are sincethe analytes are moved by electrophoretic force from micellar phase.
Stacking with Reverse Migrating Micelles and a Water Plug ModeSRW has proved to be an effective on-line concentrating technique for
some hydrophobic compounds. A more than 40-fold enhancement indetection sensitivity has been achieved in the determination of phenoxyacid herbicides.[37] In SRW, the sample is prepared in a matrix havinga conductance lower than the separation buffer and including the surfactantat a concentration slightly higher than the critical micelle concentration(CMC). SRW complements SRMM for concentrating hydrophobic analytesbecause the micelles in the sample matrix can increase the solubility ofthe analytes. Unlike NSM, REPSM, and SRMM, a water plug is introducedinto the capillary from the inlet after conditioning the capillary with acidicBGS, followed by the injection of the sample. The low pH BGS is adoptedto reduce the surface charge of the capillary and thus to lower the bulkEOF. Then, Separation is finished under reverse voltage with BGS bothin the inlet and outlet vials. The focusing mechanism of SRW is also basedon the abrupt change in effective analyte electrophoretic velocities at thestacking boundary. Therefore, sample matrix, sample size, and water plug
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length are the three main factors affecting the concentrating efficiency ofthe analytes.[38]
Field-Enhanced Sample Injection with ReverseMigrating Micelles
FESI-RMM is a mode that sample is prepared in low conductivity micel-lar matrix and electrokinetically injected into the capillary after injectingshort plug of water. The steps and mechanisms involved in FESI-RMMare shown in Figure 3. The capillary is first filled with the micellar solution,and then a water plug is hydrodynamically injected. After that, the sampleprepared in a micellar matrix is electrokinetically injected from the inlet ofthe capillary under reverse voltage. At the same time, the outlet of thecapillary is still in the micellar BGS vial. In the electrokinetic injection,the electric field enhanced in the water plug can make micelles and neutralanalytes solubilized in them generate electrophoretic velocities greaterthan the bulk electro-osmotic flow, and enter the capillary. While theneutral analytes are being brought to the boundary between the waterand the BGS, the water plug is being pumped out from the capillary bythe EOF. Once 90%–99% of the original current (depending on the kindof analyte and analytical parameters) has been reached, that is, when thewater plug has been considerably removed from the capillary, the sample
FIGURE 3 FESI-RMM mode to neutral analytes. A) a water plug is hydrodynamically injected into thecapillary conditioned with BGS; B) a sample prepared in a micellar matrix is electrokinetically injectedunder negative voltage; C) the sample vial is replaced by the BGS when the current reaches 90%–99% ofits normal value; and D) the separation of analytes occurs by MEKC.
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vial is replaced by the BGS, and analytes begin being separated undernegative voltage. Under these conditions, 1000–3000 stacking enhance-ment factors in terms of peak area can be observed.[39]
ON-LINE SAMPLE SWEEPING TECHNIQUES
Sweeping is an on-line sample preconcentration technique fornonpolar molecules in MEKC. The sweeping steps in which acidic BGSis used are shown in Figure 4. First, a sample is prepared in a matrix voidof the micelles used. Due to the difference between conductivities ofsample matrix and BGS does not significantly affect the focusing effect ofsweeping; therefore, the sample matrix can be accepted whether itsconductivity is higher, similar, or lower than the BGS. The sample is hydro-dynamically introduced into the capillary after conditioning of the capillarywith low pH micelle BGS. Second, the BGS is placed in the inlet vial,a negative polarity is applied, and then micelles enter the sample solutionzone and sweep the analytes. Finally, once the analytes are totally accumu-lated by micelles at the boundary between the sample and the BGS,the resultant separation occurs by MEKC. Sweeping can also be carriedout with neutral or alkaline micelle BGS. It is different as normal voltage
FIGURE 4 Sweeping mode to neutral analytes. A) a large volume of sample prepared in a matrix withthe similar conductivity to the BGS but free of micelles is hydrodynamically introduced into the capillaryconditioned with low pH micelles BGS; B) the inlet of capillary is placed in the vial with BGS and micellesenter sample zone and sweep the analytes under a negative voltage; C) the analytes are totally swept whenthe micelles completely fill the sample zone; and D) the separation of analytes occurs by MEKC.
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is applied and the analytes are picked up by micelles at the front boundaryof the sample plug. The examples using this sweeping can be found inthe separation of some agrochemicals.[40–45] The effectiveness of on-linesample sweeping techniques depends on the affinity of analytes to themicelles. Neutral analytes are separated by partitioning alone, whereascharged analytes are separated based on partitioning and electrophoresis.[46]
Both charged and neutral analytes can be preconcentrated, which makes thisenrichment technique versatile.
COMBINATION OF STACKING AND SWEEPING TECHNIQUES
Cation Selective Exhaustive Injection Sweeping
Cation selective exhaustive injection-sweeping (CSEI-sweeping) is a combi-nation of two on-line preconcentration techniques, sample stacking withelectrokinetic injection and sweeping, that can provide more than 35000-foldincreases in detection sensitivity.[47,48] The steps for CSEI-sweeping usinganionic micelles as the pseudostationary phase are illustrated in Figure 5.
FIGURE 5 CSEI-sweeping-MEKC mode to cationic analytes. A) a zone of high-conductivity bufferwithout micelles followed by a short water plug is hydrodynamically introduced; B) the cationic analytesprepared in a low-conductivity solution are electrokinetically injected; C) both the ends of capillaryare placed in the vials with micellar BGS after injection stop; D) the anionic micelles enter thecapillary and sweep the stacked and introduced analytes to the narrow bands as the polarity of voltageis switched; and E) the analytes are separated by MEKC.
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The column is conditioned with a nonmicellar BGS at low pH in order tosuppress the EOF. A zone of a high-conductivity buffer devoid of micelles(HCB) followed by a short water plug is hydrodynamically introduced.Then, the cationic analytes prepared in a low-conductivity solution areelectrokinetically injected into the capillary. The water plug during theCSEI step helps to enhance the electric field at the tip of the capillary,which allows the cationic analytes to enter the capillary at high velocityand eventually improves the stacking effect. The HCB increases theinjected sample size and creates a narrower stacked zone after theCSEI step,[49] but does not affect the focusing effect of the sweeping steps.Once the injection is stopped and both ends of the capillary are placedin micellar BGS vials, the voltage is then switched to negative polarity.In this step, the anionic micelles will enter the capillary to sweep theintroduced and stacked analytes as the narrow bands. Finally, the analytesare separated by MEKC.
Anion Selective Exhaustive Injection Sweeping
The principle of anion selective exhaustive injection (ASEI-sweeping)technique[50] is similar to that of CSEI-sweeping-MEKC but a cationicsurfactant is used. The procedure is modified as follows. First, a polyacryla-mide (PAA)-coated capillary is conditioned with a nonmicellar BGS. Then,a zone of a high-conductivity buffer without micelles followed by a shortwater plug is hydrodynamically injected. Afterward, a low-conductivity ofanion sample solution is electrokinetically injected under negative voltage,and the anions move rapidly toward the outlet. At the same time, the waterplug is moving out from the inlet of the capillary. When the current isstable, injection is stopped and both vials at inlet and outlet are transferredto micellar BGS and the voltage is reversed to begin separating. At this time,cationic micelles will enter the capillary and sweep the focused samplezone as a narrow band. The anions swept by the micelles are separatedby MEKC mode. Under optimized conditions, ASEI-sweeping can providean approximately 100000-fold improvement in peak heights for somephenoxy acidic herbicides.[51]
CHROMATOGRAPHIC PRECONCENTRATION
On-Line Solid Phase Extraction-CE Techniques
On-line solid phase extraction (SPE)–CE is a relatively novel techniquethat has advantages such as less sample manipulation, avoiding contami-nation to samples, and considerable consumption of solvents. It can also
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be used as a cleanup method to remove undesirable components fromthe sample. The potential of this procedure for the analysis of agro-chemicals has been demonstrated in several publications. In on-lineSPE–CE coupling, the SPE column is separated from CE, but an inter-face is required to introduce compatible desorption volumes intothe CE. In addition, the other main objective of the interface is to solvethe problem from the volume difference between the SPE-elutionplug and conventional hydrodynamic injection volume in CE.[52] Thetypical interfaces can be classified as vial, valve, or T-piece-type. A sensitivityenhancement factor of 1000-fold has been obtained using a micro-C18
trapping column CE system with a microvalve.[53] As the sample matrixdoes not enter the electrophoretic system in on-line SPE-CE, adsorp-tion effects of sample matrix are minimized. Additionally, electro-phoretic analysis is not affected by the SPE sorbent because of the SPEbeing separated from CE.
However, the construction of SPE-CE coupling is complicated. Theconnection of the SPE column and CE capillary generally produce deadvolume at the interface, which make band broadening sometimes inevi-table. Moreover, the required desorption solvent is usually on the orderof microliters, much larger than the tolerable injection volume in CE and,therefore, only a small part of the eluted sample can be usually introducedinto the separation capillary. This leads to a drop in preconcentrationefficiency.
In-Line SPE–CE Techniques
In-line SPE–CE is a technique that completely integrates the pre-concentration SPE step into the CE system, and as a result the separationvoltage is applied across the SPE sorbent. The main advantage of thistechnique is that it is easily automated with fewer sample-handling steps.In general, in-line SPE-CE can be performed by using different strategies:one is the use of an open tubular (OT) capillary in which the SPE sorbentis coated in the capillary walls;[54–56] another is the use of a packedbed;[57–59] or monolithic material,[60–63] in which an SPE microcartridgeor analyte concentrator (AC) containing the packing material sorbentis kept near the inlet side of the CE capillary; and the last one is theuse of a thin impregnated membrane or SPE material positioned betweentwo capillaries. However, the separating and concentrating efficiencydepends on the volume and the composition of the solvent. Moreover,when complex samples are analyzed, the adsorption of sample matrixcomponents on the capillary walls can cause the problems such asclogging or irreproducible results.
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Molecularly Imprinted Polymer-CapillaryElectrochromatagraphy/CE Techniques
The molecularly imprinted polymer (MIP)-based capillary electrochroma-tography (CEC) is regarded as a selective and highly effective separation sys-tem. For some applications, MIP-CEC=CE allows the analytes separated frommatrix components to be directly introduced into the capillary, thus avoidingthe clean-up steps in the analysis of complex samples, which obviously wouldconsiderably diminish the total analysis time.[64] In recent years, the study ofMIP-CEC=CE has prompted increased attention for the improvement of thesynthesis procedures of the imprinted capillary columns. Several formatshave been described, such as packed capillary columns,[65] MIP entrapmentin acrylamide or silica networks,[66] particles grafted MIP on surface,[67]
monoliths,[68,69] capillary coatings,[70] and the capillary column partiallyfilled with MIP nanoparticles[71] have been the most successful.
Synthesis of MIPs is a process in which cross-linked polymers areformed around a template molecule. After the template is removed, a largenumber of cavities will form. These cavities contain functional groupscapable of binding to the template molecules which enable the polymerto rebind the template molecules selectively. The high selectivity andstability of the MIP made it useful as the stationary phase sorbent incapillary electrochromatography.
APPLICATIONS IN THE ANALYSIS OF AGROCHEMICALRESIDUES
Many applications of CE combined with on-line preconcentrationhave been published in recent years. In this review, on-line samplepreconcentration techniques in CE are focused on the determination ofagrochemical residues, such as herbicides, fungicides, and insecticides,in different samples. Table 1 lists the applications in the analysis of theseagrochemical residues by official chromatographic method and the CEwith on-line preconcentration. A number of the methods of determiningmixed agrochemicals, plant hormones, or raw materials of agrochemicalsare also listed in this table.
Applications in the Analysis of Herbicides
Hernandez-Borges et al.[72] developed a CE–mass spectroscopy (MS)assay in which NSM was used to preconcentrate the triazolopyrimidinesulfonanilide herbicides in soy milk. The MS can provide much higherselectivity and better sensitivity than UV. SPE was applied together withon-line preconcentration procedures NSM in order to improve the LODs.
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Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
TABLE
1A
pp
lica
tio
no
fC
Ew
ith
On
-Lin
eP
reco
nce
ntr
atio
nin
An
alys
iso
fA
gro
chem
ical
Res
idu
es
Agr
och
emic
alC
lass
Agr
och
emic
alN
ame
Sam
ple
Typ
eP
reco
nce
ntr
atio
nM
eth
od
Co
nce
ntr
atio
nF
acto
rL
OD
LO
Do
fC
hro
mat
ogr
aph
icM
eth
od
s
Her
bic
ides
[8]
Dic
losu
lam
,cl
ora
nsu
lam
met
hyl
,fl
um
etsu
lam
,m
eto
sula
m,
flo
rasu
lam
Min
eral
and
stag
nan
tw
ater
s
SPE
-NSM
,SP
E-S
WM
R(L
VSS
wit
hp
ola
rity
swit
chin
g)
NSM
:8–
11-f
old
;SW
MR
:14
3–21
4-fo
ldN
SM:
133–
195mg
=L
;SW
MR
:6.
5–11
.9mg
=L
HP
LC
-UV
:24
9–40
2mg
=L
[12
8]
Her
bic
ides
[9]
Mo
nu
ron
,is
op
rotu
ron
,d
iuro
nSp
iked
tap
and
po
nd
wat
erSP
E-S
RM
M>
500-
fold
10–3
0p
pb
SPE
-HP
LC
-UV
:0.
010–
0.06
2mg
=L
(20mL
inj.)
;0.
026–
0.09
1mg
=L
(10mL
inj.)
[12
9]
Her
bic
ides
[11
](p
-su
lfo
ph
enyl
)ace
tic,
2-(p
-su
lfo
ph
enyl
)p
rop
ion
ic,
2-(p
-su
lfo
ph
enyl
)b
uty
ric,
3-(p
-su
lfo
ph
enyl
)b
uty
ric,
4-(p
-su
lfo
-ph
enyl
)bu
tyri
c,5-
(p-s
ulf
op
hen
yl)
vale
rian
icac
id
En
viro
nm
enta
lsa
mp
leN
SM4–
6n
g=m
LH
PL
C:
0.02
–0.0
7m
g=L
[13
0]
Her
bic
ides
[16
]P
araq
uat
,d
iqu
at,
dif
en-z
oq
uat
Dri
nki
ng
wat
erF
ESI
-RM
M2.
9–3.
9mg
=L
HP
LC
-UV
:0.
72–0
.68mg
=L
[13
2]
Her
bic
ides
[21
]C
hlo
rin
ated
acid
En
viro
nm
enta
lw
ater
NSM
-CE
-UV
,NSM
-CE
-el
ectr
osp
ray(
ES)
-MS
3-fo
ldN
SM-C
E-U
V:
8–25
0mg
=L
,N
SM-C
E-E
S-M
S:<
1mg
=L
GC
-ele
ctro
nca
ptu
red
etec
tor
(EC
D):
0.07
–249
mg=L
[13
1]
Her
bic
ides
[22
]P
araq
uat
,d
iqu
atE
nvi
ron
men
tal
wat
erN
SM-C
E-M
S10
-fo
ld9–
20mg
=L
HP
LC
-UV
:0.
72–0
.68mg
=L
[13
2]
Her
bic
ides
[37
]F
eno
pro
p,
mec
op
rop
,d
ich
lorp
rop
SRM
M,
FE
SI-R
MM
,SR
W,
swee
pin
gSR
MM
:90
–158
-fo
ld,
FE
SI-R
MM
:72
–94-
fold
,SR
W:
37–4
9-fo
ld,
Swee
pin
g:5–
7-fo
ld
SPE
-HP
LC
:0.
075–
0.75
0mg
=
g[13
3]
Her
bic
ides
[47
]P
araq
uat
,d
iqu
at,
and
dif
enzo
qu
atT
apw
ater
CSE
I-sw
eep
ing-
ME
KC
,sw
eep
ing
CSE
I-sw
eep
ing-
ME
KC
:35
000–
5100
0-fo
ld,
s-w
eep
ing:
250–
500-
fold
CSE
I-sw
eep
ing-
ME
KC
:0.
075–
1mg
=L
,sw
eep
ing:
10.1
–13.
0mg
=L
HP
LC
-UV
:0.
72–0
.68mg
=L
[13
2]
Her
bic
ides
[51
]4-
(2,4
-Dic
hlo
rop
hen
oxy
)b
uty
ric
acid
,2,
4,5-
tric
hlo
rop
he-
no
xyac
etic
acid
(2,4
,5-T
),2-
(2,4
,5-
tric
hlo
rop
hen
oxy
)p
rop
ion
icac
id,
4-ch
loro
ph
en-o
xyac
etic
acid
,2,
4-d
ich
loro
ph
eno
xyac
etic
acid
,2-
(2,4
-dic
hlo
rop
hen
oxy
)p
rop
ion
icac
id
ASE
I-sw
eep
ing-
ME
KC
1000
00-f
old
100
pg=
mL
GC
wit
hh
alid
e-sp
ecif
icd
etec
tor:
40–1
10n
g=L
[13
4]
1478
Dow
nloa
ded
by [
Uni
vers
itat P
olitè
cnic
a de
Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
Her
bic
ides
[72
]C
lora
nsu
lam
-met
hyl
,m
eto
sula
m,
flu
met
sula
m,
flo
rasu
lam
,d
iclo
sula
m
Soy
mil
kSP
E-N
SM-C
E-U
V=M
SN
SM-C
E-U
V:
133–
195mg
=L
;N
SM-C
E-M
S:74
–150
mg=L
Her
bic
ides
[73
]C
hlo
rin
ated
acid
En
viro
nm
enta
lw
ater
FASS
(FE
SI)-
CE
-CC
D63
2–10
78-f
old
0.05
6–0.
270
pp
mG
C-E
CD
:0.
075–
1.3mg
=L
[13
1]
Her
bic
ides
[74
]D
eam
ino
met
rib
uzi
n,
dea
min
od
iket
om
etri
bu
zin
,d
iket
om
etri
bu
zin
En
viro
nm
enta
lw
ater
and
soil
LV
SSw
ith
po
lari
tysw
itch
ing
4–36
-fo
ld10
–20
ng=
LL
C-M
S-M
S:1.
25–2
2.5mg
=kg
[13
6]
Her
bic
ides
[75
]N
ico
sulf
uro
n,
thif
ensu
lfu
on
(met
hyl
),tr
iben
uro
n-m
eth
ly,
sulf
om
etu
ron
-met
hyl
,p
yraz
osu
lfu
ron
-eth
yl,
chlo
rim
uro
n-e
thyl
Cer
eals
LV
SSan
dp
ola
rity
swit
chin
g57
0–83
5-fo
ld0.
22–0
.89
ng=
gSP
E-H
PL
C:
0.01
–0.0
2m
g=kg
[13
5]
Her
bic
ides
[76
]F
enu
ron
,sim
azin
e,at
razi
ne,
carb
aryl
,am
etri
n,
pro
met
ryn
,te
rbu
tryn
En
viro
nm
enta
lw
ater
On
-lin
eSP
E-C
E12
-fo
ld0.
01–0
.03mg
=m
LG
C-f
lam
eio
niz
edd
etec
tor
(FID
):0.
015–
0.02
5mg
=L
,G
C-n
itro
gen
-ph
os
ph
oru
s(N
PD
):.5
ng=
L[1
37
]
Her
bic
ides
[77
]s-
tria
zin
es,
ph
eno
xyac
ids
Par
tial
-fil
lin
gM
EK
C-
CE
-dio
de
arra
yd
etec
tor
(DA
D)=
CE
-ESI
-MS
CE
-DA
D:
0.12
–0.2
9m
g=L
,C
E-E
SI-M
S0.
027–
0.07
5m
g=L
GC
-NP
D:
0.03
–0.0
7mg
=L
[13
8]
Her
bic
ides
[78
]B
arb
itu
rate
s,p
hen
ylu
rea,
tria
zin
eR
F-M
EK
C(S
RM
M)
GC
-NP
D:
0.03
–0.0
7mg
=L
[13
8]
Her
bic
ides
[79
]P
hen
oxy
acid
En
viro
nm
enta
lsa
mp
leFA
EP
(FE
SI-R
MM
)29
87–3
479-
fold
0.01
–0.0
5n
g=m
LG
Cw
ith
hal
ide-
spec
ific
det
ecto
r:40
–110
ng=
L[1
34
]
Her
bic
ides
[80
]4-
chlo
rop
hen
ol,
3-ch
loro
ph
eno
l,2-
chlo
rop
hen
ol,
2,4-
di-c
hlo
rop
hen
ol,
2,4,
5-tr
ich
loro
ph
eno
l,p
enta
chlo
rop
hen
ol,
2,2-
dim
eth
yl-2
,3-
dih
ydro
ben
zo[b
]fu
ran
-7-o
l
dei
on
ized
and
tap
wat
erFA
SS(F
ESI
)10
�7–1
0�9
MG
C-E
CD
:0.
075–
1.3mg
=L
[13
9]
Her
bic
ides
[81
]U
nd
eriv
atiz
edch
lori
nat
edac
idE
nvi
ron
men
tal
wat
erSP
E-F
ASS
(FE
SI)
5000
–10,
000-
fold
0.26
9–20
.3p
pt
GC
-EC
D:
0.07
5–1.
3mg
=L
;[14
0]
Her
bic
ides
[82
]F
lum
etsu
lam
,fl
ora
sula
m,
clo
ran
sula
m-m
eth
yl,
dic
losu
lam
,m
eto
sula
m
Soil
SPE
-FA
SI(F
ESI
)18
–34mg
=kg
HP
LC
-UV
:9.
38–1
4.1mg
=kg
[12
8]
Her
bic
ides
[83
]D
esis
op
rop
ylat
razi
ne,
des
eth
ylat
razi
ne,
sim
azin
e,h
ydro
xyat
razi
ne,
atra
zin
e,p
rop
azin
ean
dp
rom
etry
n
Dri
nki
ng
wat
ers
RE
PSM
-ME
KC
4–10
-fo
ld3.
3–8.
5mg
=L
LC
-ele
ctro
spra
yio
niz
atio
n(E
SI)-
MS-
MS:
0.01
–0.0
43mg
=L
[14
1]
(Continued
)
1479
Dow
nloa
ded
by [
Uni
vers
itat P
olitè
cnic
a de
Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
TABLE1
Co
nti
nu
ed
Agr
och
emic
alC
lass
Agr
och
emic
alN
ame
Sam
ple
Typ
eP
reco
nce
ntr
atio
nM
eth
od
Co
nce
ntr
atio
nF
acto
rL
OD
LO
Do
fC
hro
mat
ogr
aph
icM
eth
od
s
Her
bic
ides
[84
]P
rop
ham
e,ca
rbo
fura
n,
par
ath
ion
eth
yl,
chlo
rfen
vin
-p
ho
s,at
razi
ne,
sim
azin
e,d
esm
etry
n,
2,4-
D,
diu
ron
En
viro
nm
enta
lw
ater
SPE
-RE
PSM
-ME
KC
5000
–100
00fo
ld0.
0014
–0.0
8n
g=L
GC
-FID
:0.
015–
0.02
5mg
=
L,G
C-N
PD
:1.
5n
g=L
[13
7]
Her
bic
ides
[85
]M
etri
bu
zin
,le
nac
il,
eth
ofu
mes
ate,
atra
zin
e,te
rbu
tryn
,is
o-
pro
turo
n,
chlo
roto
luro
n,
lin
uro
nan
dd
egra
dat
ion
pro
du
cts
En
viro
nm
enta
lw
ater
SPE
-RE
PSM
,SP
E-H
CSS
M0.
13–2
.73mg
=L
SPE
-HP
LC
-UV
:0.
010–
0.06
2mg
=L
(20mL
inj.)
;0.
026–
0.09
1mg
=L
(10mL
inj.)
[12
9]
Her
bic
ides
[86
]2,
4-D
ich
loro
ph
eno
xyac
etic
acid
,2,
4-d
ich
loro
ben
zoic
acid
,4-
amin
o-3
,5,6
-tri
ch-lo
rop
ico
lin
icac
id,
3,5-
dic
hlo
rob
enzo
icac
id,
2-(2
,4,5
-tri
chlo
rop
hen
oxy
)p
rop
ion
icac
id
En
viro
nm
enta
lw
ater
SBM
E-F
AE
P(F
ESI
-R
MM
)-N
AC
E0.
08–0
.14
ng=
mL
Liq
uid
-liq
uid
-liq
uid
mic
roex
trac
tio
n(L
LL
ME
)-H
PL
C:
0.5
ng=
mL
[14
2]
Her
bic
ides
[87
]2,
4-d
ich
loro
ph
eno
xyac
etic
acid
,2,
4,5-
tric
hlo
rop
hen
-oxy
acet
icac
id,
2-(2
,4-d
ich
-lo
rop
hen
oxy
)pro
pio
nic
acid
,2-
(2-m
eth
yl-4
-ch
loro
ph
eno
xy)
pro
pan
oic
acid
Tap
wat
erSP
E-F
ASS
(FE
SI)-
CE
-P
GD
1-4�
10�
2n
g=m
LG
C-M
S:0.
1–0.
2mg
=L
[14
3]
Her
bic
ides
[88
]T
rias
ulf
uro
n,
rim
sulf
uro
n,
flaz
asu
lfu
ron
,m
etsu
lfu
ron
-m
eth
yl,
chlo
rsu
lfu
ron
Wat
eran
dgr
ape
SPE
-LV
SSw
ith
po
lari
tysw
itch
ing
wat
er:
0.04
–0.1
2mg
=L
,gr
ape:
0.97
–8.3
0mg
=kg
LC
-UV
:0.
1p
pb
[14
4]
Her
bic
ides
[89
]s-
tria
zin
eSw
eep
ing
usi
ng
aca
tio
nic
surf
acta
nt
9–15
ng=
mL
GC
-FID
:0.
015–
0.02
5mg
=
L,G
C-N
PD
:1.
5n
g=L
[13
7]
Her
bic
ides
[90
]P
araq
uat
,d
iqu
at,
dif
enzo
qu
atD
rin
kin
gw
ater
SPE
-SR
MM
0.2–
2.2mg
=L
HP
LC
-UV
:0.
72–0
.68mg
=L
[13
2]
Her
bic
ides
[91
]am
ino
ph
osp
ho
nic
acid
sIn
-cap
illa
ryd
eriv
atiz
a-ti
on
-CE
-LIF
2–65
mg=L
LC
-UV
:8–
10mg
=L
,[14
5]
GC
-MS:
0.05
mg=
kg[1
46
]
Her
bic
ides
[92
]A
traz
ine
En
viro
nm
enta
lsa
mp
leIn
-lin
em
on
ocl
on
alan
tib
od
ies-
CE
1000
-fo
ldP
pb
GC
-NP
D:
0.03
-0.0
7mg
=L
[13
8]
Her
bic
ides
[93
]A
traz
ine,
des
eth
ylat
razi
ne,
des
iso
pro
pyl
atra
zin
e,d
eset
hyl
-d
esis
op
rop
ylat
razi
ne
Uri
ne
In-li
ne
MIP
-CE
0.2–
0.6mg
=m
L
Fu
ngi
cid
es[1
4]
Tri
adim
eno
lSR
MM
-CD
EK
C8–
11-f
old
0.8–
3.8
pp
mL
C-M
S-M
S:0.
001
mg=
kg(s
oil
,str
aw)[1
47
]
1480
Dow
nloa
ded
by [
Uni
vers
itat P
olitè
cnic
a de
Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
Fu
ngi
cid
es[1
5]
Flu
dio
xon
il,
pro
cym
ido
ne,
pyr
ipro
xyfe
n,
din
ose
b,
carb
end
azim
Fru
its
and
vege
tab
les
Swee
pin
g,SR
Wan
dSR
MM
Swee
pin
g:10
-fo
ld,
SRW
:30
-fo
ld,
SRM
M:
50-f
old
Swee
pin
g:0.
02–0
.04mg
=m
L,
SRW
:0.
01–0
.03mg
=m
L,
SRM
M:
0.00
2–0.
02mg
=m
L
HP
LC
-UV
:8.
7–25
.0mg
=L
,[14
9]
SDM
E(S
ingl
ed
rop
mic
roex
trac
tio
n)-
GC
-MS:
0.00
1–0.
017mg
=g,
[15
0]
LC
-MS-
MS:
0.01
–0.6
06mg
=kg
[16
7]
Fu
ngi
cid
es[4
4]
Pic
oxy
stro
bin
,pyr
aclo
stro
bin
Uri
ne
Swee
pin
g7.
0–9.
6mg
=L
Fu
ngi
cid
es[4
5]
azo
xyst
rob
in,
kres
oxi
m-m
eth
yl,
pyr
aclo
stro
bin
Fru
its
and
vege
tab
les
swee
pin
g40
3–86
1-fo
ld0.
001–
0.00
2m
g=kg
LC
-DA
D:
0.2
mg=
kg[1
48
]
Fu
ngi
cid
es[9
4]
Pyr
imet
han
il,
nu
arim
ol,
pro
cym
ido
ne,
cyp
rod
inil
Win
eR
EP
SM-M
EK
C38
.3–2
41mg
=L
HP
LC
-UV
:0.
026mg
=m
L[1
51
]
Fu
ngi
cid
es[9
5]
Th
iab
end
azo
le,
pro
cym
ido
ne
Fru
its
and
Veg
etab
les
SPE
-LV
SS-C
E-M
S0.
005–
0.05
mg=
kgM
IP-H
PL
C-f
luo
resc
ent
det
ecto
r(F
LD
):0.
03mg
=L
[15
2]
Fu
ngi
cid
es[9
6]
Pro
pic
on
azo
le,
teb
uco
naz
ole
,fe
nb
uco
naz
ole
Fru
its
Swee
pin
g-C
D-M
EK
C30
–100
-fo
ld0.
09–0
.1mg
=m
LQ
uE
Ch
ER
S-L
C-M
S:0.
01m
g=kg
[15
3]
Fu
ngi
cid
es[9
7]
4-C
hlo
rop
hen
ol,
4-et
hyl
ph
eno
l,3-
met
hyp
hen
ol
Swee
pin
g54
–100
-fo
ld19
–28
pp
bL
C-U
V:
1.5mg
=L
,LC
-EC
:0.
01–0
.05mg
=L
[15
4]
Fu
ngi
cid
es[9
8]
Hex
aco
naz
ole
,p
enco
naz
ole
,m
yclo
bu
tan
ilSR
MM
-CD
-ME
KC
,sw
eep
ing-
CD
-ME
KC
Swee
pin
g:62
–67-
fold
,SR
MM
:9–
10-f
old
SRM
M:
1.2–
4m
g=L
,sw
eep
ing:
0.1–
0.2
mg=
LL
C-M
S-M
S:0.
25–7
.5n
g=m
L[1
55
]
Fu
ngi
cid
es[9
9]
Th
iab
end
azo
leC
itru
sM
IP-C
EC
0.04
–0.0
5m
g=kg
MIP
-H
PL
C-F
LD
:0.
03mg
=L
,[15
2]
Fu
ngi
cid
es[1
00
]P
yolu
teo
rin
Soil
FASS
(FE
SI)
0.10
7–0.
36mg
=m
LH
PL
C:
10mg
=m
L[1
00
]
Mix
edag
roch
emic
als[1
3]
Pir
imic
arb
,m
etal
axyl
,P
yrim
eth
anil
,p
rocy
mid
on
e,n
uar
imo
l,az
oxy
stro
bin
,te
bu
fen
ozi
de,
fen
arim
ol,
ben
alax
yl,
pen
con
azo
le,
tetr
adif
on
Red
win
esSP
ME
-RE
PSM
-ME
KC
0.04
9–1.
69m
g=L
HP
LC
-UV
:0.
026mg
=m
L[1
51
]
HP
LC
:0.
006–
0.02
0p
pm
,[15
6]
GC
-NP
D:
0.13
–4.5mg
=L
[15
7]
Mix
edag
roch
emic
als[1
01
]M
eth
om
yl,
asu
lam
,ca
rben
da-
zim
,al
dic
arb
,car
bet
amid
e,p
rop
oxu
r,p
irim
icar
b,
carb
aryl
,ca
rbo
fura
n,
met
hio
carb
In-li
ne
SPE
-CE
16–7
2-fo
ld1–
16n
g=m
LH
PL
C-U
V:
0.02
–3.2mg
=L
,[15
8]
Qu
EC
hE
RS
wit
hG
C-M
S:1
pp
b,[1
59
]
Soli
d-p
has
em
icro
extr
acti
on
(SP
ME
)-H
PL
C-E
SI-M
S:0.
01.1
.2n
g=m
L[1
60
]
Mix
edag
roch
emic
als[1
02
]P
irim
icar
b,
met
alax
yl,
pyr
imet
han
il,
pro
cym
ido
ne,
nu
arim
ol,
azo
xyst
rob
in,
teb
ufe
no
zid
e,fe
nar
imo
l,b
enal
axyl
,p
enco
naz
ole
,te
trad
ifo
n
Ro
sew
ines
SPM
E-R
EP
SM-
ME
KC
0.04
0–0.
929
mg=
LH
PL
C-U
V:
0.02
6mg
=m
L,[1
51
]
HP
LC
:0.
006–
0.02
0p
pm
,[15
6]
GC=N
PD
:0.
13–
4.5mg
=L
[15
7]
(Continued
)
1481
Dow
nloa
ded
by [
Uni
vers
itat P
olitè
cnic
a de
Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
TABLE1
Co
nti
nu
ed
Agr
och
emic
alC
lass
Agr
och
emic
alN
ame
Sam
ple
Typ
eP
reco
nce
ntr
atio
nM
eth
od
Co
nce
ntr
atio
nF
acto
rL
OD
LO
Do
fC
hro
mat
ogr
aph
icM
eth
od
s
Mix
edag
roch
emic
als[1
03
]P
yrim
eth
anil
,p
rocy
mid
on
e,n
uar
imo
l,fe
nar
imo
l,b
enal
axyl
,p
enco
naz
ole
,p
irim
icar
b
To
mat
oes
RE
PSM
-ME
KC
0.13
4–0.
476
mg=
kgG
C-M
S;L
C-F
LD
:0.
02–1
.0m
g=kg
,[16
1]
GC=N
PD
:0.
13–4
.5mg
=L
[15
7]
Mix
edag
roch
emic
als[1
04
]C
arb
end
azim
,P
irim
icar
b,
met
alax
yl,
pyr
imet
han
il,
pro
cym
ido
ne,
nu
arim
ol,
azo
xyst
rob
in,
teb
ufe
no
zid
e,fe
nar
imo
l,b
enal
axyl
,p
enco
naz
ole
,te
trad
ifo
n
Wat
erR
EP
SM-M
EK
C33
.6–2
16mg
=L
LC
-MS:
<0.
2p
pb
,[16
5]
GC
-NP
D:
0.13
–4.5mg
=L
,[15
7]
Dis
per
sive
liq
uid
–liq
uid
Mic
roex
trac
tio
n(D
LL
ME
)-H
PL
C:
0.5.
1.0
ng=
mL
[16
6]
Mix
edag
roch
emic
als[1
05
]C
arb
end
azim
,p
irim
icar
b,
met
alax
yl,
pyr
imet
han
il,
pro
cym
ido
ne,
nu
arim
ol,
azo
xyst
rob
in,
teb
ufe
no
zid
e,fe
nar
imo
l,b
enal
axyl
,p
enco
naz
ole
,te
trad
ifo
n
Win
eSP
ME
-RE
PSM
-ME
KC
0.05
4–0.
113
mg=
LH
PL
C-U
V:
0.02
6mg
=m
L[1
51
]
HP
LC
:0.
006–
0.02
0p
pm
,[15
6]
GC=N
PD
:0.
13–4
.5mg
=L
[15
7]
Mix
edag
roch
emic
als[1
06
]A
mit
role
,car
ben
daz
im,
2-am
ino
ben
zim
idaz
ole
,th
iab
end
azo
le,
1,2-
dia
min
ob
enze
ne
LV
-tIT
P7.
6–27
-fo
ld0.
014–
0.13
mg=
LSP
E-L
C:
4–10
mg=kg
,[16
2]
DL
LM
E-H
PL
C:
0.5–
1.0
ng=
mL
[16
6]
Mix
edag
roch
emic
als[1
07
]P
irim
icar
b,
pyr
ifen
ox,
Pen
con
azo
l,ca
rben
daz
im,
cyro
maz
ine,
pyr
imet
han
il,
cyp
rod
inil
Min
eral
wat
erFA
SI(F
ESI
)-N
AC
E8.
80–2
6.2mg
=L
LC
-UV
:0.
025
mg=
L,[1
63
]
DL
LM
E-H
PL
C:
0.5–
1.0
ng=
mL
[16
6]
Mix
edag
roch
emic
als[1
08
]C
ypro
din
il,
cyro
maz
ine,
pyr
ifen
ox,
pir
imic
arb
,p
yrim
eth
anil
Juic
eN
SM,
FE
SI,
RP
-SW
MR
(LV
SSw
ith
po
lari
tysw
itch
ing)
RP
-SW
MR
:27
2-fo
ld;
RP
-NSM
:9–
29-f
old
NSM
:0.
06–0
.28
mg=
L,
FE
SI:
0.02
–0.0
8m
g=L
,R
P-S
WM
R:
0.00
2–0.
043
mg=
L
LC
-UV
:0.
025
mg=
L[1
63
]
Mix
edag
roch
emic
als[1
09
]C
arb
end
azin
,sim
azin
e,A
traz
ine,
pro
paz
ine,
amet
ryn
,d
iuro
n,
lin
uro
n,
carb
aryl
,p
rop
oxu
r
Fru
its
and
vege
tab
les
Swee
pin
g,SR
W,
m-S
RM
M3–
18-f
old
Swee
pin
g:3.
6–43
mg=L
,SR
W:
5.3–
46mg
=L
,m
-SR
MM
:2.
7–35
mg=L
GC
-MS;
LC
-FL
D0.
02–1
.0m
g=kg
,[16
1]
LC
-UV
:14
–28mg
=kg
,[16
4]
LC
-MS-
MS:
0.01
–0.6
06mg
=kg
[16
7]
Mix
edag
roch
emic
als[1
10
]P
irim
icar
b,
carb
end
azim
Dri
nki
ng
wat
erIn
-lin
eSP
E–C
ZE
7.8�
103–1
3.6�
103-f
old
0.1mg
=L
LC
-MS:
<0.
2p
pb
[16
5]
Inse
ctic
ides
[40
]A
ceta
mip
rid
,im
idac
lop
rid
,th
iam
eth
oxa
mV
eget
able
Swee
pin
g44
3–78
8-fo
ld5.
6–25
mg=kg
Ult
rap
erfo
rman
celi
qu
idch
rom
ato
-gr
aph
y-M
S-M
S:0.
1–6mg
=kg
[16
8]
1482
Dow
nloa
ded
by [
Uni
vers
itat P
olitè
cnic
a de
Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
Inse
ctic
ides
[41
]C
arb
ofu
ran
,C
arb
aryl
Veg
etab
lean
dfr
uit
Swee
pin
g-N
AM
EK
C67
8–75
8-fo
ld7.
9–31
mg=kg
GC
-fla
me
ther
mio
nic
det
ecto
r(F
TD
):0.
02–0
.10
mg=
kg[1
69
]
Inse
ctic
ides
[42
]C
hlo
rdim
efo
rm,
sem
iam
itra
zch
lori
de
Ho
ney
Swee
pin
g11
00–1
000-
fold
0.62
–0.8
8mg
=kg
Inse
ctic
ides
[43
]C
arb
amat
esJu
ice
DL
LM
E-S
wee
pin
g-M
EK
C1–
7mg
=L
LC
:0.
8–1.
9n
g=m
L[1
70
]
Inse
ctic
ides
[11
1]
Car
bam
ate
En
viro
nm
enta
lsa
mp
leFA
SS(F
ESI
)-M
EK
C30
-fo
ld2.
5�
10�
4–2
.9�
10�
3M
HP
LC
-UV
:0.
02–3
.2mg
=L
[15
8]
Inse
ctic
ides
[11
2]
Cyp
rom
azin
e,m
elam
ine
Rea
lm
ilk
sam
ple
CSE
I-sw
eep
ing-
ME
KC
6222
–917
9-fo
ld43
.7–2
3.4
pg=
mL
Inse
ctic
ides
[11
3]
Neo
nic
oti
no
idin
sect
icid
esC
ucu
mb
ersa
mp
leD
LL
ME
-sw
eep
ing-
ME
KC
3985
–991
8-fo
ld0.
8–1.
2n
g=g
LC
-MS-
ESI
:0.
1–0.
5m
g=kg
[17
1]
Inse
ctic
ides
[11
4]
Car
bar
yl,
met
acra
te,
carb
ofu
ran
,is
op
roca
rbV
eget
able
and
fru
itO
n-li
ne
LL
LM
E-
stac
kin
g11
00-f
old
2–4
ng=
mL
GC
-FT
D:
0.02
–0.1
0m
g=kg
,[16
9]
LC
-MS-
MS:
0.01
–0.6
06mg
=kg
[16
7]
Inse
ctic
ides
[11
5]
Ald
icar
b,
carb
ofu
ran
,is
op
rotu
ron
,ch
loro
tolu
ron
,m
eto
lach
lor,
mec
op
rop
,d
ich
lorp
rop
,M
CP
A,
2,4-
D,
met
ho
xych
lor,
TD
E,
DD
T,
die
ldri
n,
DD
E
Co
nta
min
ated
wat
erSP
E-F
ESS
(FE
SI)-
ME
KC
0.04
–0.4
6n
g=m
L
Inse
ctic
ides
[11
6]
Met
ho
myl
,p
rop
oxu
r,ca
rbo
fura
n,
carb
aryl
,is
op
roca
rb,
pro
mec
arb
Fru
itju
ice
RE
PSM
–ME
KC
4–13
-fo
ld0.
01–0
.10
mg=
LG
C-F
TD
:0.
02–0
.10
mg=
kg[1
69
]
Inse
ctic
ides
[11
7]
Car
bam
ate
pes
tici
des
Ap
ple
DL
LM
E-s
wee
pin
g-M
EK
C49
1–18
34-f
old
2.0–
3.0
ng=
gG
C-F
TD
:0.
02–0
.10
mg=
kg[1
69
]
Inse
ctic
ides
[11
8]
N-m
eth
ylca
rbam
ate
pes
tici
des
Par
tial
fill
ing
(PF
)-M
EK
C-E
SI-M
S,SR
MM
-ME
KC
-ESI
-MS
PF
-ME
KC
–ESI
-MS:
0.08
–1.8mg
=m
L,
SRM
M:
0.04
–2.0mg
=m
L
HP
LC
-FL
D:
0.5–
4.0mg
=L
[17
2]
Inse
ctic
ides
[11
9]
Ino
rgan
icar
sen
icsp
ecie
sE
nvi
ron
men
tal
wat
erL
VSS
-HSC
(hig
h-s
ensi
-ti
vity
cell
)-C
ZE
5.61
—17
.1mg
=L
HP
LC
-ind
uct
ivel
yco
up
led
pla
sma-
MS:
0.16
–0.6mg
=L
[17
3]
Raw
mat
eria
lso
fag
roch
emic
als[3
]A
nil
ine,
o-t
oli
din
e,o
-to
luid
ine,
m-a
min
op
hen
ol
En
viro
nm
enta
lw
ater
FE
SI0.
29–0
.43
ng=
mL
Raw
mat
eria
lso
fag
roch
emic
als[2
4]
Pri
ori
typ
oll
uta
nt
ph
eno
lsL
VSS
-NA
CE
>10
0-fo
ld0.
001–
0.08
mg=m
L
Raw
mat
eria
lso
fag
roch
emic
als[4
9]
Aro
mat
icca
rbo
xyli
cac
ids,
dan
syl
amin
oac
ids,
dis
ulf
on
icac
ids
nap
hth
alen
edis
ulf
on
icac
ids
ASE
I-Sw
eep
-ME
KC
1000
–600
0-fo
ld0.
8–1.
2p
pb
(Continued
)
1483
Dow
nloa
ded
by [
Uni
vers
itat P
olitè
cnic
a de
Val
ènci
a] a
t 17:
26 2
4 O
ctob
er 2
014
TABLE1
Co
nti
nu
ed
Agr
och
emic
alC
lass
Agr
och
emic
alN
ame
Sam
ple
Typ
eP
reco
nce
ntr
atio
nM
eth
od
Co
nce
ntr
atio
nF
acto
rL
OD
LO
Do
fC
hro
mat
ogr
aph
icM
eth
od
s
Raw
mat
eria
lso
fag
roch
emic
als[1
20
]C
hlo
rop
hen
ols
,ch
loro
ph
eno
xyac
ids
LV
SSw
ith
po
lari
tysw
itch
ing;
Swee
pin
g-M
EK
C
LV
SSw
ith
po
lari
tysw
itch
ing:
27–4
0-fo
ld;
Swee
pin
g-M
EK
C:
3–7-
fold
LV
SSw
ith
po
lari
tysw
it-
chin
g:0.
005–
0.01
mg=
L;
swee
pin
g-M
EK
C:
0.1–
0.25
mg=
L
GC
-EC
D:
0.01
–2m
g=L
[17
4]
Raw
mat
eria
lso
fag
roch
emic
als[1
21
]2,
4-D
imet
hyl
ph
eno
l,2,
3,5-
trim
eth
ylp
hen
ol,
2,4-
dic
hlo
ro-
ph
eno
l,2-
cho
loro
ph
eno
l,2,
4-d
init
rop
hen
ol
En
viro
nm
enta
lsa
mp
leF
ESI
-ME
KC
904–
2692
-fo
ld2.
5–8
ng=
mL
LC
-ele
ctro
chem
ical
det
ecto
r(E
D):
3–8
ng=
L[1
75
]
Raw
mat
eria
lso
fag
roch
emic
als[1
22
]M
on
och
loro
acet
icac
id,
mo
no
bro
mo
acet
icac
id,
dic
hlo
roac
etic
acid
,d
ibro
mo
acet
icac
id,
bro
mo
chlo
roac
etic
acid
,tr
ich
loro
acet
icac
id
Dri
nki
ng
wat
erL
VSS
97–1
20-f
old
0.02
7–0.
053
mg=
L
Raw
mat
eria
lso
fag
roch
emic
als[1
23
]2,
4-d
ich
loro
ph
eno
l,2,
4,5-
tric
hlo
rop
hen
ol
En
viro
nm
enta
lw
ater
In-li
ne
SPE
-CE
1600
0-fo
ld25
–17
pg=
mL
LC
-ED
:3–
8n
g=L
[17
5]
Raw
mat
eria
lso
fag
roch
emic
als[1
24
]2,
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The optimized protocol provided the LODs of these triazolopyrimidineherbicides in soy milk at 74mg=L. Xu et al.[73] determined 16 chlorinatedacid herbicides in environmental water by CZE with contactless conductivitydetection (CCD). The capillary was coated with poly (vinyl alcohol) andon-line FESI was used. The LODs in water samples were 0.056–0.270 ppm,and sensitivity was enhanced up to 632–1078-fold.
Quesada-Molina et al.[74] reported a method analyzing metribuzindegradation products, deaminometribuzin (DA), deaminodiketometri-buzin (DADK), and diketometribuzin (DK), with CE by means of on-lineLVSS with polarity switching. The analytes were dissolved in sodium tetra-borate buffer. The herbicides extracted from spiked water and soil sampleswere concentrated using off-line SPE step that was employed to furtherimprove sensitivities and extend the method to real samples. LVSS withpolarity switching provided preconcentration factors of 4, 36, and 28 forDK, DA, and DADK, respectively. A 500-fold preconcentration was obtainedby the method for the case of water samples and of 2.5-fold in the case ofsoil samples. Recently, a MEKC method analyzing six sulfonylurea herbicideresidues in cereals by mean of on-line LVSS with polarity switching wasdeveloped by Yi et al.,[75] in which a sample plug up to 33.11 cm wasintroduced into a capillary with 50 cm effective length. The enrichmentfactors for these six sulfonylureas were between 570-fold and 835-fold.Their LODs were down to 0.22–0.89 ng=g.
On-line SPE-CE has been applied to determine s-triazines in environ-mental samples.[76] The process of analysis including calibration, precon-centration, elution, and injection into the sample vial was automaticallycarried out by a capillary electrophoresis system coupling a continuousflow system via a programmable arm. The whole system was completelycontrolled by a computer. The separation of s-triazine herbicides wasachieved within 13 min, and the detectable concentration was down to50 mg=L, whereas the enrichment factor was 12-fold. The partial fillingtechnique has also been used for the determination of herbicide residuesby CE.[77,78] One of these examples is the work reported by Menzingeret al.[77] They analyzed s-triazines and phenoxy acids by the partial-fillingtechnique and non-aqueous capillary electrophoresis (NACE) with UVdetection. These conditions can be also compatible with ESI-MS detectionproviding LODs of 0.12–0.29 mg=L.
Applications in the Analysis of Fungicides
The fungicides were usually separated by MEKC with REPSM.[13,102–105]
The fungicides from spiked wine samples were extracted by a solid-phasemicroextraction (SPME). Quantitative extraction from wine samples spikedat two concentration levels (range 0.18–6.00 mg=L) was carried out in
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triplicate. LODs were between 0.040 and 0.929 mg=L, which are below themaximum residue limits (MRLs) in wine grapes set by the Spanish andEuropean legislation.[102] Poor detection sensitivity was often producedfrom matrix effects (interfering peaks) in the extraction of fungicideresidues. In order to solve the problem, a matrix-matched calibration wasdeveloped with spiked samples. Ravelo-Perez et al.[103] analyzed sevenfungicides by MEKC with REPSM, in which the matrix matched calibrationcurves were developed with spiked tomato samples and the SPME was usedto extract the analytes from samples. A linear range under this conditionwas 0.5 to 2.5 mg=kg. In a follow up research, they developed the CZEmethod proper to MS detection.[95] The phosphate buffer was replacedwith a more volatile ammonium formate buffer. Off-line SPE coupledwith on-line LVSS were employed to further improve LODs allowing theseanalytes to be determined down to the levels of 1=10 MRLs.
Ibrahim et al.[96] developed a method of cyclodextrin (CD)-MEKC withsweeping for the determination of propiconazole, tebuconazole, andfenbuconazole. The strong interaction between analytes and chargedpseudostationary phase enhanced sensitivity 30–100-fold. Wang et al.[45]
recently analyzed three strobilurin fungicide residues in fruits andvegetables by MEKC with sweeping. The enrichment factors of azoxy-strobin, kresoxim-methyl, and pyraclostrobin were 861, 550, and 403,respectively. Their LODs were 0.002, 0.001, and 0.002 mg=kg, respectively.
Cacho et al.[99] separated thiabendazole (TBZ) in citrus samples by themolecularly imprinting capillary electrochromatography. A molecularlyimprinted monolith (MIM) was synthesized and as stationary phase, itsselectivity to TBZ was evaluated by nonaqueous capillary electrochromato-graphy. The high selectivity achieved by the MIP-CEC allowed unambi-guous detection and quantification to TBZ in citrus samples by directinjection of the crude sample extracts, without any previous clean-up, in lessthan 6 min. The limits of quantitation (LOQs) were in the range of0.04–0.05 mg=kg which was below the established MRLs. Takeda et al.[106]
separated five mixed agrochemicals including fungicides, insecticide, andherbicide by large volume injection in conjunction with transient isotacho-phoresis (ITP). LODs to the five agrochemicals were on the ppm level underthe optimized separation and UV detection condition. The enrichment factorsobtained from the comparison of the LODs were 7.6–27-fold.
Applications in the Analysis of Insecticides
Recently, Chen’s research team published their works in succession,in which sweeping was used to preconcentrate three chloronicotionyls,[40]
two carbamates,[41] in vegetables and two amidines in honey.[42] Theenrichment factors were 626, 788, and 443 for acetamiprid, imidaclorid,
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and thiamethoxam in vegetables under the injection condition of 10 kV�120 s. In the separation of two amidine acaricides, chlordimeform, andsemiamitraz in honey were concentrated 1100-fold and 1000-fold. A novelnonaqueous MEKC with sweeping was used to separate two carbamates invegetables. The enrichment factors were 678 for carbofuran and 758 forcarbaryl under the optimized conditions. The buffer consisted of 100 mMSDS, 30 mM sodium acetate, and formamide-acetonitrile (85:15, V=V),and its apparent pH was 9.4. The samples were hydrodynamically injectedfor 1 kPa� 150 s.
The three online preconcentration techniques associated with MEKCwere used to analyze nine agrochemicals including the two commonly usedinsecticides, carbaryl and propoxur, from drinking water and vegetablesextracts, and their performances were evaluated.[109] These three techni-ques included sweeping, SRMM, and a modification of the latter, whichinvolved momentarily applying a positive voltage at the inlet vial aftersample injection. Enrichment factors of 3–18-fold and LODs in the rangeof 2–46 mg=L were reported. Rodrıguez-Gonzalo et al.[110] determined pir-imicarb and carbendazim in drinking water by in-line SPE–CE employeda synthesized monolithic bed. This method allowed samples to be loadedat flow rates of about 65 mL=min by applying a pressure of 12 bar. A 5-cmlength of monolithic sorbent was used to preconcentrate the target analytesfrom aqueous samples. After preconcentrating drinking water for 15 min,these pesticides could be detected at the level of 0.1mg=L, as demandedby current EU legislation.
Tegeler et al.[111] applied MEKC with FESI to preconcentrate andseparate carbamate insecticides and compared decanoyl-N-methylglu-camide (MEGA 10) surfactant with the traditionally used SDS surfactant.As a result, MEGA 10-borate micellar system produced twice as manynumber of plates per minute as did the SDS micellar system. The reportedLODs were in the range of 2.5� 10�4–2.9� 10�3 M.
An exciting result was obtained[112] when cypromazine (CYP) andmelamine (MEL) in real milk samples were concentrated and separatedby means of on-line CSEI-sweeping technique, in which the sensitivitieswere enhanced 6222-fold for CYP and 9179-fold for MEL and the achievedLODs were between 43.7 and 23.4 pg=mL. The optimum buffer consistedof 100 mM SDS, 50 mM phosphoric acid (pH¼ 2.0), and 15% acetonitrile(V=V) and the sample was injected at 10 kV for 600 s.
Zhang et al.[113] separated some neonicotinoid insecticides by usingdispersive liquid–liquid microextraction (DLLME) coupled with sweepingin MEKC. The novelty of this work was the application of DLLME-sweepingto isolate and preconcentrate the insecticide residues in cucumber. Underoptimized conditions, the enrichment factors were achieved in the rangefrom 4000 to 10,000 and the LOQs were in the range of 0.8 to 1.2 ng=g.
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CONCLUSIONS
CE has undoubtedly become a compelling alternative to chromato-graphic techniques owing to the on-line preconcentration technology. Itis especially useful for the determination of agrochemical residues thatcannot be separated efficiently by HPLC and require derivatization to beanalyzed by GC. Compared with other off-line preconcentration techniques,these on-line techniques have the obvious advantages such as simplicity,economy, and high separation efficiency in the focusing of both neutraland charged analytes. The signals of analytes can be enhanced up to severalthousand-folds without significant deterioration in separation efficiency.However, the excellent techniques must be successful in the applying toreal samples and getting good reproducibility. It is gratifying that they havebeen successfully employed in determination of agrochemical residuesboth in environmental and food samples. The both reproducibility andrecovery can meet the requirements of the legislation in some developedcountries and regions.
Pursuing lower and lower LOD is an eternal topic to analyticalchemistry, of course, also to the analysis of agrochemical residues. For thispurpose, combining the fortes of two even more on-line preconcentrationmeans together should be a developing tendency. Among these combi-nations, C=ASEI-sweeping provides the best sensitivity enhancementfor charged analytes. Furthermore, a combination of on=in-line SPE withstacking and sweeping method is also expected. Other combinations oftwo on-line preconcentration techniques, such as micelle-mediated neutralanalyte isotachophoretic (MM-ITP) concentration and micelle to solventstacking (MSS) of organic cations, should be possible. In the future,multi-template MIP-CEC=CE is anticipated.
FUNDING
This work is supported by the Specialized Research Fund for theDoctoral Program of Higher Education, Ministry of Education, China,(Grant No. 20093227110010) and The Science Fund of Jiangsu University(Grant No. 08JDG001). The authors are grateful to A Project Funded bythe Priority Academic Program Development of Jiangsu Higher EducationInstitutions.
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