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    Talanta 65 (2005) 9297 Talent 65 (2005) 92-97

    Direct determination of toxic trace metals in honey and sugars using DirectDetermination of toxic trace metals in honey and sugars Usinginductively coupled plasma atomic emission spectrometry inductively coupled plasma

    atomic emission spectrometryMD Ioannidou, GA Zachariadis Ioannidou MD, GA Zachariadis, AN Anthemidis, JA Stratis , AN Anthemidis, JA StratisLaboratory of Analytical Chemistry, Department of Chemistry, Aristotle University ofThessaloniki, GR-541 24 Thessaloniki, Greece Laboratory of Analytical Chemistry,Department of Chemistry, Aristotle University of Thessaloniki, GR-541 24Thessaloniki, GreeceReceived 19 January 2004; received in revised form 24 March 2004; accepted 12May 2004 Received 19 January 2004, received in Revised form 24 March 2004Accepted 12 May 2004Available online 14 June 2004 Available online 14 June 2004

    AbstractAbstractA rapid method for the determination of Pb, Cd, Cu, Cr, Co, Ni, Mn and Zn in honeyand sugars without prior digestion or ashing of the A rapid method for theDetermination of Pb, Cd, Cu, Cr, Co, Ni, Mn and Zn in honey and sugars withoutPrior Digestion or ashing of thesample was developed, using inductively coupled plasma atomic emissionspectrometry (ICP-AES). WAS samples developed, using inductively coupled plasmaatomic emission spectrometry (ICP-AES). The critical instrumental parameters suchThe critical instrumental parameters Sucheas sample flow rate and radio frequency incident power were thoroughly optimized. Isample flow rate and incident radio frequency power Were Thoroughly optimized.The effect of matrix type and its concentration was also The effect of matrix type andWAS ITS Also Concentrationexamined for glucose/fructose, sucrose and honey matrices. Examined for glucose /fructo, sucrose and honey Matrices. The sensitivity was investigated using calibrationcurves obtained in presence of The sensitivity calibration curves Obtained UsingWAS investigated in Presence ofthe above matrices. Above the Matrices. The obtained recoveries for Cd, Cu, Cr, Co,Ni and Mn at the gl The Obtained recoveries for Cd, Cu, Cr, Co, Ni and Mn at the gl1 -1

    level were satisfactory and practically independent of Were Practically satisfactorylevel and independent ofthe matrix used for the calibration standards. The matrix used for the calibrationstandards. The recoveries of Pb and Zn were less sufficient. The recoveries of Pband Zn Were less sufficient. Various commercial samples of honey, sugar, Variouscommercial samples of honey, sugar,glucose and fructose were analyzed with respect to their toxic metal content. glucoseand analyzed with respect to fructo Were Their toxic metal content. The method canbe applied for routine analysis, quality and The method for routine analysis Can BeApplied, quality andenvironmental pollution control purposes at the gl Environmental Pollution Control

    Purposes at the gl1 -1

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    level of concentration, after suitable dilution of the samples. level of Concentration,Suitable after Dilutional of the samples. 2004 Elsevier BV All rights reserved. 2004 Elsevier BV All rights reserved.Keywords: Toxic metals; Honey; Sugars; Glucose; Inductively coupled plasma;Atomic emission spectrometry Keywords: Toxic metals, Honey, Sugars, Glucose,

    Inductively Coupled Plasma, Atomic Emission Spectrometry

    1. 1.IntroductionIntroductionHoney is high-viscosity liquid foodstuff containing Honey is high-viscosity liquidcontaining Foodstuffa range of nutritiously important complementary ele- the range of nutritiouslyimportant complementary ele-ments. ments. It contains a mixture of carbohydrates, such as It contains a mixture ofcarbohydrates, Suche Ifructose (2545% m/m), glucose (2537% m/m), maltose Fructo (25-45% m / m),

    glucose (25-37% m / m), maltose(212% m/m), sucrose (0.53% m/m) with traces of many (2-12% m / m), sucrose(0.5-3% m / m) with traces of Manyother sugars depending on the floral source and water Other sugars depending onthe floral source and water(1518% m/m)[1] .The mean content of mineral sub- (15-18% m / m)[1].The meancontent of mineral sub-stances in honey has been calculated to be 0.17% m/m, stances in honey HAS BeenCalculated To Be 0.17% m / m,although it varies within a wide range. although it varies Within the wide range.Honey is the result Honey is the resultof a bio-accumulation process useful for the collection of of the bio-accumulationprocess for the collection of Usefulinformation related to the environment where the bees live. information related to theenvironment WHERE live the Bees.Since the forage area of the hive is very large (more than Since the area of the hiveForage is very large (More Than7km 7km2 2) and the bees come in contact not only with air but ) And the Bees come in contactonly with air But Not

    also with soil and water, the concentration of heavy metals Also with soil and water,heavy metals of the Concentrationin honey reflects their amount in the whole region. Their honey reflects the amount inthe Whole Region. There- There-fore, honey has been recognized as a biological indicator forces, honey HAS Beenrecognized as a Biological Indicatorof environmental pollution[2] .But nevertheless, determi- of Environmental Pollution[2].But nevertheless, deter- *Corresponding author. Corresponding author. Fax: +30 2310997719. Fax: +302310997719.

    E-mail address: [email protected] (GA Zachariadis). E-mail address:[email protected] (GA Zachariadis).
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    nation of heavy metals in honey is of high interest mainly nation of heavy metals inhoney is of high interest mainlyfor quality control and nutritional aspect. for quality control and nutritional aspect.High levels of High levels ofmetals are undesirable because of their known or supposed Because of metals is

    undesirable Their Known or supposedtoxicity, so that, for instance a limit of 1 mg kg Toxicity, so That, for instance the limitof 1 mg kg1 -1for lead for leadis set in some countries[3] .Some countries is set in[3].Furthermore, sugars (such as glucose, fructose or sugar) Furthermore, sugars(glucose as Suche, fructo or infant)are classified as generally recognized safe food ingredients. is classified asGeneRally recognized safe food Ingredients.Because of their extended usage, high concern exists about Because of Their

    extended usage, concern exists about highthe contribution of these ingredients to the total dietary in- The Contribution of TheseIngredients to the Total Dietary in-take of trace metals that may be present as contaminants. take of trace metalspresent as contaminants That May Be.Specific attention has focused on lead because of increas- Attention Focused onspecific HAS Because of increas-leading knowledge of adverse health effects from lead at vari- ing knowledge of adversehealth effects from lead at vari-ous levels of exposure[4] .However, these ingredients also ous levels of exposure.[4]However, tissue Also Ingredientsserve as potential sources of exposure to other metals, such serve as potentialsources of exposure to Other metals, Sucheas cadmium, copper and tin, which occur at various levels as cadmium, copper andtin, Which occur at various levelsin the environment[5,6] .in the environment[5,6].Metals determination in sugar-rich foodstuffs has been Metals Determination insugar-rich Foodstuffs HAS Beena challenging analytical task due to the interference arising a challenging task due tothe Analytical Interference arisingfrom the matrix. from the matrix. Sample pre-treatment is usually required Sample

    pre-Treatment is usually requiredto destroy the organic matrix and to extract the metal ions to destroy the organicmatrix and to extract the metal ionsbound in organic complexes. bound in organic complexes. Obviously, the selection ofthe Obviously, the selection of thedigestion procedure must take into account the analytes, the procedure must takeinto account Digestion the analytes, the0039-9140/$ see front matter 2004 Elsevier BV All rights reserved. 0039-9140 / $- see front matter 2004 Elsevier BV All rights reserved.doi:10.1016/j.talanta.2004.05.018 doi: 10.1016/j.talanta.2004.05.018
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    MD Ioannidou et al.Ioannidou MD et al./ Talanta 65 (2005) 9297/ Talant 65 (2005)92-9793 93sample matrix and the time requirements of the analytical sample matrix and the timeof the Analytical Requirements

    technique considered. Considered technique. Several techniques have been pro-Several Techniques have Been pro-posed for the determination of heavy metals in honey and possess for theDetermination of heavy metals in honey andother sweeteners, but in most cases the matrix mineraliza- Other sweeteners, But inmost Cases the mineralized matrix-tion is required [3,4,7] . However, in common mineraliza- tion is required [3,4,7].However, in common-mineralizedtion procedures there are risks of contamination or analyte tion Procedures There areRisks of Contamination or analyticloss as a result of prolonged sample manipulation and loss as a result of prolonged

    sample manipulation andheating. heating.Flame atomic absorption spectrometry (FAAS), due to its Flame Atomic AbsorptionSpectrometry (FAAS), due to ITSrelatively low cost and quite good analytical performance relatively low cost and quitegood performance Analyticalhas been widely used for determination a various metals in Been widely used forHAS Determination of various metals inhoney [811] . The conventional way to carry such deter- Honey [8-11]. Theconventional way to carry fixed-Sucheminations involves a mineralization stage to obtain a final minations involves themineralization stage to Obtain the finalsolution suitable for introduction into the flame nebulizer Introduction into the SolutionSuitable for flame nebulizer[9] . The destruction of the organic matter eliminates both[9].The destruction of theorganic matter eliminates Bothspectral interferences and the accumulation of residues in spectral interferences andthe accumulation of residues inthe burner head and spray chamber. the spray chamber and burner head. However,a drawback is However, the drawback isposed since the linear response range of the AAS is narrow. since the linear

    response range possess of the ASA is narrow.Difficulties associated to the high organic matter content are Difficulties Associated tothe high organic matter content isovercome by dissolving the samples in acidified water and overcome by dissolvingthe samples in water and acidifiedthen directly introducing the resulting solution in the neb- THEN Directly introducingthe resulting solution in the Neb-ulizer[10] .Electrothermal atomic absorption spectrometry ulizer[10].ElectrothermalAtomic Absorption Spectrometry(ETAAS) has been proposed as a more sensitive analytical (ETAAS) HAS Beenproposed as a more sensitive Analytical

    technique compared to FAAS for the determination of toxic technique compared toFAAS for the Determination of Toxic
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    metals in honey and sugars[1,12] .metals in honey and sugars[1.12].Inductively coupled plasma-based techniques (ICP-AES Inductively coupled plasma-based Techniques (ICP-AESand ICP-MS) have been applied as multi-elemental tech- and ICP-MS) have BeenApplied as multi-element tech-

    niques for the determination of heavy metals in honey niques for the Determination ofheavy metals in honeyand other sweeteners [7,1316] . ICP-AES is attractive for and Other sweeteners[7.13 to 16].ICP-AES is attractive fortrace analysis, owing to the satisfactory sensitivity cou- trace analysis, owing to thesatisfactory sensitivity cou-pled with the advantage of simultaneous determinations blanket with the Advantageof simultaneous determinationsof several metals at several spectral lines. Several of Metals at Several spectral lines.However, the However, thegreat disadvantage of sample dry or wet digestion still re- great disadvantage of wet

    or dry sample Digestion still re-mains. Mains. Hence, the sample is usually digested by wet-acid Hence, the sampleis usually digested by wet-acidor dry ashing by heating in a microwave oven or a fur- or dry ashing by heating in amicrowave oven or a fur-nace. NACE.The aim of this study was to investigate the possibility The aim of this study toinvestigate the Possibility WASof the simultaneous and direct measurement of heavy met- of the simultaneous anddirect measurement of heavy met-als in honey and sugars using ICP-AES without any dry or als in honey and sugarsUsing ICP-AES without Any dry orwet sample dissolution. Dissolution wet sample. The effect of the matrix type and Theeffect of the matrix type andits concentration was examined using aqueous (AQ) matrix ITS WAS ConcentrationExamined Using aqueous (AQ) matrixand three different carbohydrate matrices: a 1+1 mixture of Three differentcarbohydrate and Matrices: a 1 +1 mixture ofglucose and fructose mixture (GF), sucrose (SU) and honey glucose and fructomixture (GF), sucrose (SU) and honey(HO). (HO). The sensitivity of the method with respect to each The sensitivity of the

    method with respect to Eachmetal was evaluated using the resulted slope of the calibra- Using the metal resultedWAS evaluated slope of the calibrated-tion curves. tion curves. As there are not readily available standard ref- Not readilyavailable I There are standard ref-erence materials [17,18] , the recoveries of the analytes were erence materials[17.18],the recoveries of the analytes Weremeasured at different concentrations using spiked solutions Measured at differentconcentrations Solutions Using Spikedand used as estimation of the accuracy of the method. and used as estimation of theAccuracy of the method. The The

    precision was evaluated by measuring the repeatability of evaluated by measuringthe precision WAS Repeatability of
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    the method for all analytes and at different sugar matrixes. the method for all analytesand at different sugar matrixes.The capability of the method as a routine analysis method The capability of themethod as a routine analysis methodwas estimated through the determination of the detection WAS estimated through the

    Determination of the detectionlimits of every heavy metal studied. Every heavy metal limits of studied. Theproposed method The proposed methodwas applied in a number of commercial samples of honey, Applied in the number ofWAS commercial samples of honey,sugar, glucose and fructose. sugar, glucose and fructo.Table 1 Table 1Operating conditions and description of the ICP-AES instrument OperatingConditions and description of the ICP-AES instrumentrf generator rf generator40 MHz, free-running 40 MHz, free-running

    rf incident power incident rf powerOptimized OptimizedTorch, injector, id Torch, injector, idFassel type, Alumina, 2.0 mm Fassel type, alumina, 2.0 mmArgon flow rates Argon flow ratesAuxiliary 0.5 l min Auxiliary 0.5 l min1 -1; nebulizer , Nebulizer0.85 l min 0.85 L min1 -1; plasma 15 l min ; Plasma 15 l min1 -1Air flow rate Air flow rate18 l min 18 l min1 -1Spray chamber Spray chamberScott double-pass Scott double-passNebulizer NebulizerGem tip cross flow Gem cross-flow typeSample propulsion Sample PropulsionPeristaltic pump, three channel Peristaltic pump, three channel

    Sample flow rate Sample flow rateOptimized OptimizedPolychromator/resolution Polychromator / resolutionEchelle/0.006 nm at 200 nm Echelle/0.006 nm at 200 nmDetector DetectorSegmented-array charge-coupled (SCD) Segmented-array charge-coupled (SCD)

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    2.2.ExperimentalExperimental2.1.2.1.InstrumentationInstrumentationA Perkin Elmer Optima 3100 XL axial viewing in- A Perkin Elmer Optima 3100 XLaxial viewing in-ductively coupled plasma atomic emission spectrometer ductively coupled plasma

    atomic emission Spectrometerwas used, according to the operating conditions given WAS used, According to theOperating Conditions givenin Table 1 .The analytical wavelengths for each analyte in Table 1.The Analyticalwavelengths for Each analyticwas, Pb: 220.353, 217.000, 261.418 nm; Cd: 214.440, WAS, Pb: 220.353, 217.000,261.418 nm, CD: 214 440,226.502, 228.802 nm; Cu: 324.752, 224.700, 327.393 nm; 226.502, 228.802 nm;with: 324.752, 224.700, 327.393 nm;Cr: 283.563, 284.325, 267.716 nm; Co: 228.616, 238.892, Cr: 283.563, 284.325,267.716 nm, Co 228.616, 238.892,

    230.786 nm; Ni: 221.648, 232.003, 341.476 nm; Mn: 230.786 nm, Ni: 221.648,232.003, 341.476 nm, Mn:257.610, 259.372, 260.568 nm; Zn: 213.857, 202.548, 257.610, 259.372, 260.568nm, Zn: 213.857, 202.548,206.200 nm. 206.200 nm. For the optimization of the instrument's perfor- For theoptimization of the instrument's perfor-mance different radio frequency (rf) incident power levels Mance different radiofrequency (rf) incident power levelsand sample flow rates were investigated. and sample flow rates Were investigated. and solutionsReagents and solutionsAll chemicals were of analytical reagent grade and were All reagent grade chemicalsWere of Analytical and Wereprovided by Riedel de Haen. provided by Riedel of Haen. The chemical reagentsused for The chemical reagents used forpreparation of matrix matched standards (glucose, fructose preparation of matrixmatched Standards (glucose, fructoand sucrose) were of analytical grade, provided by Riedel de and sucrose) Were ofAnalytical grade, provided by Riedel ofHaen. Haen. De-ionized water of MilliQ quality was used through- De-Ionized waterof MilliQ quality WAS used through-out. out. Mixed working standard solutions of the analytes (Pb, Mixed standard

    working solutions of the analytes (Pb,Cd, Cu, Cr, Co, Ni, Mg and Zn) were prepared by appropri- Cd, Cu, Cr, Co, Ni, Mgand Zn) Were Prepared by appropri-ate stepwise dilutions of stock standard solutions containing ETA stepwise dilutionsof standard stock solutions containing1000 mg l 1000 mg L1 -1of each analyte in 0.5 mol l Each analytic in 0.5 mol of L1 -1HNO HNO3 3

    (Riedel (Riedel
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    de Haen), according to the procedures described below. for Haen) According to theProcedures described Below.Eight-point calibration curves were obtained using ma- Eight-point calibration curvesWere Obtained Using I-trix matched standards prepared in aqueous (AQ), glu- Prepared Standards matched

    Trix in aqueous (AQ), glu-cose/fructose in water (GF), sucrose in water (SU) and Baskets / fructo in water (GF),sucrose in water (SU) andhoney in water (HO) matrix. honey in water (HO) matrix. The final mixed workingstan- The final mixed working stan-dard solutions had the following concentrations: 0.25, 0.50, Following the solutionsDard HAD concentrations: 0.25, 0.50,1.00, 2.50, 5.00, 10.0, 25.0 and 50 gl 1.00, 2.50, 5.00, 10.0, 25.0 and 50 gl1 -1for each metal. Each metal for.In case of the carbohydrate matrices, a 2% m/v solution In case of the carbohydrate

    Matrices, 2% w / v solutionof the corresponding sugar (glucose/fructose, sucrose, or of the corresponding sugar(glucose / fructo, sucrose, orhoney) was used for dilution. honey) WAS used for Dilutional. In order to check theoverall In order to check the Overallrepeatability of the ICP-AES detector two different calibra- Repeatability of the ICP-AES detector calibrate two different-tion procedures were made at two different time periods. tion made at two differentProcedures Were Time Periods.The slope of the calibration curves was used to estimate the The slope of thecalibration curves used to estimate the WASsensitivity of the method. sensitivity of the method.

    94 94MD Ioannidou et al.Ioannidou MD et al./ Talanta 65 (2005) 9297/ Talant 65 (2005)92-97Fig. Fig. 1. 1. Effect of the sample flow rate on the intensity of 50 gl Effect of thesample flow rate on the intensity of 50 gl1 -1Mn at GF matrix, at the following spectral lines and carbohydrate concentrations: ( )Mn at GF matrix, at the spectral lines and carbohydrate concentrations Following: ()

    257.610 nm

    1% m/v; ( ) 257.610 nm

    10% m/v; ( ) 259.372 nm

    1% m/v; ( ) 259.372nm10% m/v; ( ) 260.568 nm1% m/v; () 260.568 nm10% m/v. 257.610 nm to 1%w / v, () 257 610 nm to 10% w / v, () 259 372 nm to 1% w / v, () 259 372 nm to 10% w/ v, () 260 568 nm to 1% m / v, () 260 568 nm to 10% w / v.Samples of honey, glucose and fructose are considered as Samples of honey,glucose and fructo is Considered asnot homogeneous matrices due to their very high viscosity, Not very homogeneousTheir Matrices due to high viscosity,thus it is crucial to obtain representative sub-samples for thus it is crucial to Obtainrepresentative samples for sub-further analysis [7,16] . In case of honey, glucose and fructose Frther analysis

    [7.16].In the case of honey, glucose and fructo
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    samples, the sample container was warmed to ca. samples, the sample containerWAS warmed to ca. 50 50

    C in a C in thewater-bath and sonicated for 5 min. water-bath and sonicated for 5 min. Then an

    amount of 20 g Then year amount of 20 gof the sample was accurately weighed in a 250-ml beaker accurately weighed sampleof the WAS in a 250-ml Beakerand diluted with about 80 ml of doubly de-ionized water. and diluted with about 80 mlof doubly de-Ionized water.Finally, the mixture was transferred to a 1000 ml volumetric Finally, the mixture of1000 ml WAS Transferred to volumetricflask, diluted to volume with de-ionized water. flask, diluted to volume with de-Ionizedwater. The obtained The Obtainedsolution was used as a 2% m/v honey solution. WAS solution used as a 2% m / vhoney solution. In case of In case of

    sugar samples the above procedure was followed without a Above the infant samplesWAS FOLLOWED procedure without thewarming step. warming step.

    3.3.Results and discussionResults and discussion3.1.3.1.Effect of the incident rf powerEffect of the incident rf powerIn order to examine the effect of rf power on the in- In order to examine the effect of rfpower on the in-tensity, of 50 gl tensity, of 50 gl1 -1concentration level of each analyte at Concentration Level of Each analytic attwo carbohydrate concentration levels (2 and 5% m/v) in Two carbohydrateConcentration levels (2 and 5% w / v) inGF matrix, at three different power levels (1300, 1400 and GF matrix, at differentpower levels Three (1300, 1400 and1500 W) were tested. 1500 W) Were Tested. As it was found, by increasing the rf ITWAS I found, by Increasing the rfpower the intensity is also increased, for all analytes. Also the power intensity isincreased, for all analytes. How- How-ever, the plasma became unstable at 1400 and 1500 W, thus ever, the plasma at1400 and 1500 Became unstable W, thus

    the rf power was adjusted to 1300 W for the rest of the the rf power to 1300 W WASAdjusted for the rest of theexperiments. experiments. of the sample flow rateEffect of the sample flow rateIn ICP nebulizers, the sample flow rate defines the amount In ICP nebulizers, thesample flow rate defines the amountof analyte in the torch and affects the sensitivity of the of analytic in the torch andaffects the sensitivity of themethod. method. The effect of sample flow rate on the intensity was The effect ofsample flow rate on the intensity WASstudied in the range ml min studied in the range 1.0-2.0-3.0 ml min

    1 -1and the Ar flow and the flow would

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    rate in the nebulizer was adjusted to 0.800.850.90 l min Adjusted rate in thenebulizer WAS l min to 0.80-0.85-0.901 -1, ,respectively. respectively. Two matrices (GF and SU), two carbohydrate Two

    Matrices (GF and SU), two carbohydrateconcentrations 1.0 and 10% m/v) and 50 gl concentrations 1.0 and 10% w / v) and 50gl1 -1concentra- focus-tion of each analyte were used through this study. tion of analytic Were Each studyused through this. InFig.InFig.1 ,1,the effect of the sample flow rate on the intensity of Mn the effect of the sample flowrate on the intensity of Mnis demonstrated. is Demonstrated. According to the obtained results the in- ObtainedAccording to the results the in-

    tensity was increased by increasing the flow rate from 1 to WAS tensity increased byIncreasing the flow rate from 1 to2mlmin 2mlmin1 -1and levelled of over 2 ml min and levelled of over 2 ml min1 -1for all the exam- for all the exam-ined analytes. INED analytes. Also, another trend was observed: significant Also,Another trend observed WAS: Significantdepressing of the intensity, by increasing the carbohydrate depressing of theintensity, by Increasing the carbohydrateconcentration in the matrix from 1 to 10% m/v. Concentration in the matrix from 1 to10% w / v.Similar behaviour was found in presence of the other ex- Similar behavior of the WASfound in Presence Other ex-amined matrix type (SU, HO). amined matrix type (SU, HO). Moreover, the obtainedre- Moreover, the re-Obtainedsults were statistically analyzed using the paired t-test at a sults analyzed statisticallyWere Using the paired t-testat aconfidence level of 95%, in order to define the optimum confidence level of 95%, inorder to define the optimum

    value of sample flow rate. value of sample flow rate. The results in flow rates of 1 andThe results in flow rates of 1 and2mlmin 2mlmin1 -1are statistically different and in all cases the in- is statistically different in all Casesand the in-tensity at 2 ml min tensity at 2 ml min1 -1was higher. Higher WAS. However, there is not a sig- However, There is not a sig-nificant statistical difference between the results obtained at Statistical differencebetween the planners Obtained results at

    flow rate of 2 and 3 ml min flow rates of 2 and 3 ml min1 -1
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    . . Therefore, 2 ml min Therefore, 2 ml min1 -1sample sampleflow rate was selected for the rest of the experiments. flow rate for the rest of WASselected the experiments. of the carbohydrate matrixEffect of the carbohydrate matrixGenerally, the matrix type and the carbohydrate concen- GeneRally, the matrix typeand the carbohydrate concentrationtration affects significantly the viscosity of the sample and tration significantly affectsthe viscosity of the sample andconsequently the performance of ICP-AES methods. consequently the performanceof ICP-AES methods. There- There-fore, the effect of the matrix type and the carbohydrate con- forces, the effect of thematrix type and the carbohydrate con-centration on the emission intensity was investigated using centration on theemission intensity investigated Using WAS

    the GF, SU and HO matrices at increasing concentration (1.0, The GF, DM and HOMatrices at Increasing Concentration (1.0,2.0, 5.0, 10 and 25% m/v) of carbohydrates. 2.0, 5.0, 10 and 25% w / v) ofcarbohydrates. The optimum The optimum

    MD Ioannidou et al.Ioannidou MD et al./ Talanta 65 (2005) 9297/ Talant 65 (2005)92-9795 95Fig. Fig. 2. 2. Effect of matrix type and matrix concentration on the recovered Effectof matrix type and matrix Concentration on the recoveredanalyte concentration of Co230.786 nm. Concentration of Co-analytic 230.786 nm.( / ) Glucose and fructose; (/) Glucose and fructo;( / ) sucrose; ( /) honey. (/) Sucrose, (/) honey. Unfilled symbols refer to 10 glUnfilled symbols refer to 10 gl1 -1analyte analyticconcentration and filled symbols to 50 gl Filled symbols and Concentration to 50 gl1 -1. . The horizontal dotted lines The horizontal dotted linesrepresent the concentration level of 10 and 50 gl Represent the Concentration Levelof 10 and 50 gl1

    -1aqueous standard standard aqueoussolutions in absence of carbohydrate concentration. Concentration in the absence ofcarbohydrate solutions.of these concentrations defines also the dilution of the real Also defines the tissueconcentrations of Dilutional of the realsamples, which should be used in order to be analyzed. samples, in order Whichshould Be Used To Be analyzed. All Allthe studied analytes were measured at the three spectral lines Were the analytesstudied Measured spectral lines at the Threeand at two analyte concentrations 10 and 50 gl and analytic at two concentrations 10

    and 50 gl1 -1

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    , respec- , Respective-tively. tively. Indicative results on the effect of the matrix type and Indicative resultson the effect of the matrix type andconcentration on Co at two analyte concentrations appear in Concentration on Coconcentrations at two analytic Appear in

    Fig.Fig.2 . In all cases the recovery was almost the same for the2.In all Cases therecovery for the WAS Almost The Samelow carbohydrate concentrations (12% m/v) in the solution, low carbohydrateconcentrations (1-2% w / v) in the solution,while at higher concentrations the recovery decreased and while at higherconcentrations and decreased the recoverythe baseline becomes unstable. Becomes the baseline unstable. Therefore, 2% m/vcarbohy- Therefore, 2% w / v carbohy-drate concentration in the solution or 2% m/v dilution of the drate Concentration inthe solution or 2% w / v Dilutional of thesamples was adopted for further study, as a compromise be- Adopted WAS Frther

    samples for study, as a compromise be-tween sufficient sensitivity and low matrix influence. sufficient sensitivity and lowmatrix tween Influence. How- How-ever, higher concentrations (up to 10% m/v) can be used for ever, higherconcentrations (up to 10% w / v) Can Be Used Forhigher sensitivity but with lower precision. But higher sensitivity with lower precision.Statistical paired t-test was used to evaluate the differences Statistical paired t-testused to evaluated the differences WASin the values obtained using different matrices. Obtained Using the values in differentMatrices. InTable 2InTable 2results on the experimentally calculated t-values are listed Calculated results on thet-valuesexperimentally is Listedfor several analytes at two analyte concentrations, where Several analytic foranalytes at two concentrations, WHERETable 3 Table 3Slope standard error and correlation coefficients of the calibration equations for allanalytes in various matrices Slope standard error of the calibration coefficients andCorrelation equations for all analytes in various MatricesAnalyte spectral line Analytic spectral lineMatrix MatrixAqueous Aqueous

    Glucose/fructose Glucose / fructoSucrose SucroseHoney HoneyPb220.353 Pb-220 3536.1 1.4 (0.9770) 6.1 1.4 (0.9770)7.3 1.4 (0.9520) 7.3 1.4 (0.9520)5.3 2.2 (0.8111) 5.3 2.2 (0.8111)5.0 2.2 (0.7962) 5.0 2.2 (0.7962)Cd228.802 Cd-228 80261.9 0.3 (0.9999) 61.9 0.3 (0.9999)57.1 0.2 (0.9999) 57.1 0.2 (0.9999)

    57.0 1.2 (0.9994) 57.0 1.2 (0.9994)58.0 0.2 (0.9999) 58.0 0.2 (0.9999)
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    Cu324.752 Cu-324 752469 9 (0.9995) 469 9 (0.9995)474 15 (0.9985) 474 15 (0.9985)437 13 (0.9986) 437 13 (0.9986)457 31 (0.9934) 457 31 (0.9934)

    Cr283.563 Cr-283 563309 11 (0.9981) 309 11 (0.9981)285 7 (0.9990) 285 7 (0.9990)264 13 (0.9960) 264 13 (0.9960)266 9 (0.9982) 266 9 (0.9982)Co230.786 Co-230.78636.4 0.3 (0.9999) 36.4 0.3 (0.9999)33.9 0.2 (0.9999) 33.9 0.2 (0.9999)33.9 0.2 (0.9999) 33.9 0.2 (0.9999)33.0 0.3 (0.9999) 33.0 0.3 (0.9999)Ni341.476 Ni-341 476

    40.7 3.2 (0.9907) 40.7 3.2 (0.9907)43.9 1.4 (0.9984) 43.9 1.4 (0.9984)37.9 3.5 (0.9874) 37.9 3.5 (0.9874)41.5 2.4 (0.9952) 41.5 2.4 (0.9952)Mn257.610 Mn-257 6101135 5 (0.9999) 1135 5 (0.9999)1068 3 (0.9999) 1068 3 (0.9999)1052 6 (0.9999) 1052 6 (0.9999)1041 8 (0.9999) 1041 8 (0.9999)Zn213.857 Zn-213 857511 136 (0.9999) 511 136 (0.9999)114 88 (0.8161) 114 88 (0.8161)15 20 (0.4340) 15 20 (0.4340)201 65 (0.8701) 201 65 (0.8701)Table 2 Table 2Test of significance ( t-test) of the difference between carbohydrate matrices Test ofSignificance (t-test) of the difference between carbohydrate Matricesat two analyte concentrations analytic at two concentrationsAnalyte AnalyticAnalyte Analyticconcentration Concentration

    ( gl (Gl1 -1) )Comparison between matrices Comparison between Matricesttcrit critGFSU GF-SUaofGFHO GF-HOaofSUHO SU-HO

    aofCd CD
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    10 100.66 0.660.19 0.190.53 0.532.14 2.14

    Cd CD50 501.82 1.822.04 2.041.22 1.222.14 2.14Cu With10 100.08 0.081.57 1.571.49 1.49

    2.14 2.14Cu With50 500.19 0.192.60 2.602.37 2.372.14 2.14Co Co.10 100.27 0.270.63 0.630.94 0.942.14 2.14Co Co.50 500.02 0.021.28 1.280.72 0.722.14 2.14Mn Mn10 10

    1.92 1.921.54 1.540.70 0.702.14 2.14Mn Mn50 501.08 1.080.86 0.860.36 0.362.14 2.14a of

    (GF) glucose/fructose in water; (SU) sucrose in water; and (HO) (GF) glucose / fructoin water, (SU) sucrose in water, and (HO)

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    cients for all calibration curves were >0.990, except Pb and cients for all calibrationcurves Were> 0990, except Pb and

    Page 5Page 5

    96 96

    MD Ioannidou et al.Ioannidou MD et al./ Talanta 65 (2005) 92

    97/ Talant 65 (2005)92-97Zn, illustrating the good linearity in the studied range. Zn, illustrating the goodlinearity in the range studied. Very Veryhigh sensitivities were obtained in the determination of Mn high sensitivities WereObtained in the Determination of Mnfollowed by Cu, Zn, Cr, Cd, Co and Ni. FOLLOWED BY Cu, Zn, Cr, Cd, Co and Ni.The sensitivity in The sensitivity inthe determination of Pb was rather low. Determination of Pb Rather the low WAS. and precision of the methodAccuracy and precision of the methodUsually, in order to assess the accuracy of a method, stan- Usually, in order toAssess the Accuracy of the method, stan-dard reference materials are analyzed, the obtained results Dard reference materialsis analyzed, the results Obtainedare compared with the certified ones and the absolute or the is compared with thecertified ones and the absolute or therelative error is calculated. Calculated relative error is. However, an SRM materialwith However, with material SRM yearcertified metals concentration is not available for honey, as certified MetalsConcentration is not available for honey, Ialready mentioned by Caroli et al. [17,18] .These authors as- already mentioned by

    Caroli et al.[17.18].tissue authors as-cribed the lack of a honey-based certified reference material cribed the Lack of ahoney-based certified reference materialdue to its practical problems of transformation into a sta- due to practical problems oftransformation into ITS sit-ble, homogeneous mass, adequate for a certification project. ble, homogeneousmass, Adequate for the certification project.Therefore, the accuracy of the proposed method was eval- Therefore, the Accuracyof the proposed method eval-WASuated by determining the recoveries of the analytes at var- uated by determining therecoveries of the analytes at var-

    ious concentrations (1, 5, 25 and 50 gl ious concentrations (1, 5, 25 and 50 gl1 -1), using calibra- ), Using calibrate-tion curves at different matrices. tion curves at different Matrices. Results from therecovery Results from the recoveryexperiments appear inTable 4 .Quantitative recoveries were Appear experiments inTable 4.Quantitative recoveries Wereobtained at high metal concentrations (25 and 50 gl Obtained at high metalconcentrations (25 and 50 gl1 -1) and ) And

    they were independent of the matrix used. Were they independent of the matrix used.As it is shown, As it is Shown,
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    the recoveries obtained for all analyte concentrations were Obtained recoveries for allthe analytic concentrations Wereranged between 93 and 110%. ranged between 93 and 110%. The recoveries of Cdand Mn The recoveries of Cd and Mnwere very good, while those of Cu, Cr, Co and Ni were ad- Were very good, while

    Thos of Cu, Cr, Co and Ni Were adequate at the 25 and 50 gl Equator at the 25 and 50 gl1 -1levels. levels. On the other hand Pb On the Other hand Pband Zn recoveries were not satisfactory (

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    93 9391 9193 93GF GF102 102

    103 10395 9599 9986 8698 98SU SU102 102112 112103 10399 9994 94

    100 100AQ AQ25 gl 25 gl1 -194 94115 11597 9793 93102 10293 93GF GF102 102113 113106 106100 100103 10398 98SU SU102 102123 123114 114

    100 100121 121100 100AQ AQ5 gl 5 gl1 -1101 101200 200123 12396 9652 52

    96 96GF GF

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    109 109200 200134 134103 10349 49

    102 102SU SU110 110217 217144 144103 10354 54103 103AQ AQ1 gl 1 gl1 -1

    99 99nq NQnq NQnq NQnq NQ107 107GF GF106 106nq NQnq NQnq NQnq NQ113 113SU SU107 107nq NQnq NQnq NQnq NQ115 115nq: not quantified. NQ: not quantified.

    Table 5 Table 5Precision of the method at various matrices (25 gl Precision of the method at variousMatrices (25 gl1 -1of the analyte, of the analytic,relative standard deviation srelative standard deviation sr r%, n= 10) %, N= 10)Analyte AnalyticMatrix MatrixAqueous Aqueous

    Glucose/fructose Glucose / fructoSucrose Sucrose

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    Honey HoneyPb Pb6.2 6.219 1925 25

    >50 > 50Cd CD1.0 1.00.7 0.71.1 1.11.3 1.3Cu With2.8 2.82.2 2.22.5 2.51.0 1.0

    Cr Cr7.9 7.96.6 6.66.9 6.91.9 1.9Co Co.1.0 1.01.7 1.73.2 3.21.6 1.6Ni Us3.7 3.717 175.6 5.615 15Mn Mn0.3 0.30.6 0.60.5 0.50.6 0.6Zn Zn

    17 17>50 > 50>50 > 50>50 > 50Table 6 Table 6Detection limits ( gl Detection limits (gl1 -1) obtained for all analytes in aqueous and carbo- ) Obtained for all analytes inaqueous and carbo-hydrate matrices Hydra MatricesAnalyte Analytic

    Aqueous AqueousGlucose/fructose Glucose / fructo

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    Sucrose SucroseHoney HoneyPb Pb6.7 6.74.5 4.5

    9.7 9.78.6 8.6Cd CD0.7 0.71.2 1.20.9 0.91.4 1.4Cu With1.5 1.51.0 1.04.8 4.8

    1.0 1.0Cr Cr17 176.8 6.815 155.7 5.7Co Co.0.4 0.40.8 0.82.0 2.01.8 1.8Ni Us7.3 7.34.3 4.316 163.1 3.1Mn Mn0.2 0.20.2 0.21.0 1.00.2 0.2

    Zn Zn48 48139 139309 30929 29The detection limit ( cThe detection limit (cL L) was calculated according to the ) WAS Calculated According to the3 s criterion (three times the standard deviation of 10 blank And Criterion 3 (Threetimes the standard deviation of 10 blankmeasurements). Measurements). The results are listed in Table 6 .The lower The

    results is Listed inTable 6.The lower
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    detection limits were obtained for Mn, Cd, Co and Cu, mod- Were Obtained detectionlimits for Mn, Cd, Co and Cu, a-erate for Cr, Ni and Pb and higher for Zn. corrections for Cr, Ni and Pb and higher forZn. Consequently, the Consequently, thedetectability of the proposed method is considered satisfac- detectability of the

    proposed method is Considered meet-tory for routine analysis and quality control. tory for routine analysis and qualitycontrol. Similar detec- Similar detection-tion limits for Mn, Cd, Co and Cu have been also obtained tion limits for Mn, Cd, Coand The Also have Been Obtainedusing ICP-AES after a preliminary mineralization stage [15] .Using ICP-AES after apreliminary stage mineralization[15].The ion chromatographic and the voltammetric determina- The ion chromatographicand voltammetric caused thetion of the elements Pb, Cd, Cu, Co and Ni gave much tion of the elements Pb, Cd,Cu, Co and Ni Gave much

    higher detection limits (40, 15, 3, 2 and 4 gl higher detection limits (40, 15, 3, 2 and 4gl1 -1, respec- , Respective-tively) [3] after laborious mineralization stage. tively)[3]fter laborious mineralizationstage. On the other On The Otherhand, lower detection limits for Pb, Cd, Cu and Zn were hand, lower detection limitsfor Pb, Cd, Cu and Zn Werereported only in case of using the ETAAS technique [1] .Reported only in case ofETAAS Using the technique[1].3.6. 3.6. Analysis of commercial samples of honey and sugars Analysis ofcommercial samples of honey and sugarsSamples of five commercial products of honey, two of Samples of five commercialproducts of honey, two ofsugar, one of glucose and one of fructose were analyzed infant, one of glucose andone of fructo Were analyzedwith respect to their content in heavy metals. with respect to heavy metals in Theircontent. The final The finalconcentrations of the analytes (in mg kg concentrations of the analytes (in mg kg1 -1) were calcu- ) Were calculating

    lated relative to the initial sample mass and corrected for lated relative to the initialsample mass and corrected forany dilutions. Any dilutions. Honey, glucose, fructose and sugar samples Honey,glucose, sugar and fructo sampleswere pre-treated as described in Section 2 . The results of Were Treated asdescribed in the pre-Section 2.The results ofmean concentrations and their standard deviation are listed Their mean and standarddeviation concentrations is Listedin Table 7 .Zn and Pb were not quantified due to their poor in Table 7.Zn and PbWere Not quantified due to poor Theirrepeatability, as it is given inTable 5 .Chromium was not Repeatability, as it is given

    inTable 5.Chromium Was Not