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Analytical Methods

Determination of sodium, potassium, calcium, magnesium, zinc and iron in

emulsified chocolate samples by flame atomic absorption spectrometry

C.V.S. Ieggli, D. Bohrer *, P.C. do Nascimento, L.M. de Carvalho

Departamento de Química, Avenida Roraima, 1000, Universidade Federal de Santa Maria, 97110-970 Santa Maria, RS, Brazil

a r t i c l e i n f o

 Article history:Received 21 January 2010

Received in revised form 14 July 2010

Accepted 18 July 2010

Keywords:

Emulsion

ChocolateFlame atomic absorption spectrometry

a b s t r a c t

In this study, oil-in-water formulations were optimized to determine sodium, potassium, calcium, mag-nesium, zinc, and iron in emulsified chocolate samples by flame atomic absorption spectrometry (FAAS).

This method is simpler and requires fewer reagents when compared with other sample pre-treatmentprocedures and allows the calibration to be carried out using aqueous standards. Octyl stearate was used

as oily phase. Tween 80 and Triton X100 were tested as surfactants. The optimum type and proportion of formulations were determined and their choice depended on the element studied. The emulsion prepa-ration was performed by a conventional method that involves mixing both phases at 75 ± 5  C by mag-

netic stirring and phase inversion to change the water-to-oil ratio by increasing the volume of the

surfactant-water external phase and correspondingly decreasing the volume of internal phase. The vali-dation of the method was performed against a baking chocolate standard reference material (SRM 2384)and recoveries ranged from 88.6% for K to 105.5% for Zn. The proposed method allowed the evaluation of 

the essential metal status of chocolate with minimum sample manipulation and was reproducible and

economical. 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Chocolate is a product obtained from Theobroma cacao beans. Inorder to process cacao beans into chocolate or cocoa, they are leftto ferment, dried, roasted and, finally, triturated until they are

transformed into a liqueur. Primary chocolate categories are dark,milk and white. The first is made by mixing cocoa liqueur, cocoabutter, sugar and vanilla. The second uses the same process, withthe increment of milk, and the white does not include the cocoa li-

queur, only the cocoa butter, milk and sugar (Afoakwa, Paterson, &Fowler, 2007).

Chocolate is consumed all over the world, in all segments of society and by people of all ages. Nowadays, the consumer is more

and more concerned with the nutritional status of foodstuff and,considering that chocolate is an extremely rich source of manyessential minerals, it can contribute to a healthy diet. Nevertheless,the evaluation of nutrient ingestion is a very complex task

(Borchers, Keen, Hannum, & Gershwin, 2000). The available nutri-tional data are frequently old and incomplete and in many casesunreliable due to lack of description of the analytical procedures(Ribeiro, de Morais, Colugnati, & Sigulem, 2003).

The determination of metals in foods has become an importantfield in food analysis (Reyes & Campos, 2006). However, the accu-

rate determination of metals in chocolate is still an analytical chal-lenge, due to difficulties arising from matrix characteristics. Flame

atomic absorption spectrometry (FAAS) is a powerful detectiontechnique for determining elements in the ppm range. The advan-tages of FAAS include well-characterized interferences, low opera-

tor skill required for operation, and comparatively low cost of instrumentation and maintenance (Welz & Sperling, 1999). How-ever, direct chocolate analysis by FAAS is not possible and thedetermination of metals in this type of matrix necessarily involves

sample digestion, considering that it contains a high content of or-ganic compounds.

The literature reports methods for chocolate sample treatmentinvolving microwave digestion, wet digestion, and dry ashing

(Dahiya, Karpe, Hegde, & Sharma, 2005; Güldas, 2008; Jalbaniet al., 2007; Sepe, Costantini, Ciaralli, Ciprotti, & Giordano, 2001).Acids and peroxides are usually added to improve sample decom-position. All these procedures result in additional steps, which may

lead to inconveniences such as contamination and losses duringhandling (Viñas, Pardo-Martínez, & Hernández-Córdoba, 2000).

Direct emulsification with surfactants provides a rapid proce-dure for sample preparation since this approach does not require

any destruction of the organic matrix (Sanz-Medel, de la Campa,Gonzalez, & Fernandez-Sanchez, 1999). It simply reduces the vis-cosity and the organic content of the sample, making the proper-ties of the chocolate sample close to those capable of being

analyzed by FAAS, while maintaining the system’s homogeneity

0308-8146/$ - see front matter    2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.foodchem.2010.07.043

*  Corresponding author. Fax: +55 55 3220 8870.

E-mail address:  ndenise@quimica.ufsm.br (D. Bohrer).

Food Chemistry 124 (2011) 1189–1193

Contents lists available at   ScienceDirect

Food Chemistry

j o u r n a l h o m e p a g e :  w w w . e l s e v i e r . c o m / l o c a t e / f o o d c h e m

http://dx.doi.org/10.1016/j.foodchem.2010.07.043mailto:ndenise@quimica.ufsm.brhttp://dx.doi.org/10.1016/j.foodchem.2010.07.043http://www.sciencedirect.com/science/journal/03088146http://www.elsevier.com/locate/foodchemhttp://www.elsevier.com/locate/foodchemhttp://www.sciencedirect.com/science/journal/03088146http://dx.doi.org/10.1016/j.foodchem.2010.07.043mailto:ndenise@quimica.ufsm.brhttp://dx.doi.org/10.1016/j.foodchem.2010.07.043

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and stability. In earlier studies, emulsification of samples was sat-isfactorily used for the analysis of whole hen eggs measuring Se by

graphite furnace atomic absorption spectrometry (GFAAS) and Na,K, Ca, Mg, Zn and Fe by FAAS. The oil-in-water emulsion stabilizedthe sample, maintaining the system’s homogeneity, and reducedthe viscosity and the organic content of the sample, thus allowing

egg sample analysis by GFAAS and by FAAS ( Ieggli, Bohrer, do

Nascimento, & de Carvalho, 2010; Ieggli et al., 2009).The goal of this study was to investigate the use of emulsions assample preparation for routine determination of Na, K, Ca, Mg, Zn

and Fe in chocolate by FAAS. The expected advantages of this pro-cedure are the higher stability and easy handling of sample emul-sions, allowing the use of aqueous standards for calibration. Thereliability of the procedure was checked by analyzing standard ref-

erence material.

2. Experimental

 2.1. Instrumentation/procedure

All measurements were carried out using an ANALYTIK Jena AG

(Jena, Germany) model novAA 300 atomic absorption spectrometerequipped with SpectrAA (Varian, Australia) hollow cathode lampsas the radiation source. An acetylene-air or acetylene-nitrous oxideflame was used; the gas flow rates and the burner height were ad-

 justed in order to obtain the maximum absorbance signal for each

element. Other instrumental parameters were set to the valuesshown in Table 1.

 2.2. Reagents and samples

All reagents were of analytical grade, and all emulsions wereprepared with distilled and deionized water that was further puri-

fied by a Milli-Q high purity water device (electrical resistivity of 18.0 MX cm) (Millipore, Bedford, USA). Laboratory glassware was

kept overnight in 10% (v/v) HNO3  in ethanol solution and shortlybefore use was washed with water and dried in a dust free environ-ment. Concentrated nitric acid used in this study was supplied byMerck. Sodium, potassium, calcium, magnesium, zinc, and ironstandard solutions (1000 mg L 1) were obtained from the National

Institute of Standards and Technology (NIST, USA) and diluted asnecessary to obtain working standards. The non-ionic surfactantsTriton X100 (Fluka) and Tween 80 (Fluka) were tested for emulsionpreparation. Octyl stearate (Galena, Brazil) was used as the oily

phase. The certified reference material (CRM) SRM 2384 BakingChocolate (NIST) was used to check the accuracy of the proposedmethod.

The chocolate samples analyzed in this study were purchased in

supermarkets from Santa Maria (Brazil) and the percentage of co-

coa varied. The chocolate samples were five white chocolate(brands: Neugebauer, Nestlé Classic, Lacta Laka, Neugebauer Dupy,Garoto), five milk chocolate (Neugebauer, Nestlé Classic, Lacta,

Neugebauer Dupy, Garoto), and seven dark chocolate (Neugebauer,

Nestlé Classic, Lacta Amaro, Neugebauer Dupy, Garoto, 70% CocoaNeugebauer and Dark & Soft 50% Cocoa Lacta).

 2.3. Emulsion preparation

Oil-in-water emulsions were prepared using a specific sequencein order to guarantee their stability. Aliquots of surfactant, oil and

chocolate samples or reference material were weighed and placedin an 80 mL beaker, and then heated water (65  C for Triton X100and 75  C for Tween 80, see Section 3.2) was added with continu-ous agitation until the required volume was reached. Magnetic

stirring (3000 rpm) was maintained during 15 min at room tem-perature (22  C). The total volume of the system was 50 mL, whichwas attained by increasing the volume of the surfactant-waterexternal phase and correspondingly decreasing the volume of 

internal phase. A blank emulsion was prepared in the same waywithout sample addition.

Sample amounts varied between 0.2% and 8.0% (w/v) according

to the expected amount of the analyte in the sample. For compo-nents present in larger concentrations, such as sodium, potassium,calcium and magnesium, the emulsion was prepared with a maxi-

mum sample amount of 0.2%. On the other hand, for smalleramounts of zinc and iron, between 2.0% and 8.0%, were necessary.

 2.4. Experimental design and stability study

A preliminary factorial design was applied to investigate theinfluence of oil and emulsifier amounts on emulsion stability. Theirinfluence on emulsion stability was evaluated using a 2 3 full facto-

rial design. The design required a total of nine experiments per oil/emulsifier combination.

 2.5. Emulsion stability

Stability of optimized emulsion was monitored by measuring

the extent of gravitational phase separation. The best formulationsfrom experimental design were monitored by the creaming test.For the measurement of physical stability, 10 mL of each prepared

chocolate emulsion was poured into a graduated tube and kept atroom temperature (25 C). The volume of the separated creamlayer in each tube was recorded after 1, 2, 7, 14, and 21 days of storage. The emulsion stability index (ESI) was calculated as per-

centage: ESI (%) = (remaining emulsion height/initial emulsionheight) 100. The ESI was calculated to show the stability of theemulsions since the larger the ESI value the higher emulsionstability.

3. Results and discussion

An emulsion is a thermodynamically stable system composed of water, oil and surfactant (Sinko, 2008). Based on this concept,

emulsions have been little exploited as an analytical tool by usingall the ideal conditions to produce an adequate and stableemulsion.

In order to utilize emulsions as sample preparation for FAAS

measurements, some criteria should be taken into account in theformulation planning: the emulsion should contain only the com-ponents necessary to stabilize the sample, in other words, sample,surfactant, water and, if necessary, an additional oily component;

the emulsion should be stable for a reasonable period, whichshould last during a time interval long enough to complete thedetermination procedure; the emulsion should present low viscos-ity to allow correct sample aspiration; and all components should

present low metal contamination and low background during theFAAS measurement.

 Table 1

Instrumental parameters for element determination in emulsified chocolate samples.

Element Wavelength(nm)

Slit width(nm)

I 

(mA)Integrationtime (s)

Flame

Potassium 766.5 0.8 4.5 3.0 C2H2–air

Calcium 422.7 1.2 4.0 3.0 N2O–C2H2Sodium 589.0 0.8 3.0 3.0 C2H2–air

Zinc 213.9 0.5 6.0 3.0 C2H2–air

Magnesium 285.2 1.2 4.0 3.0 C2H2–air

Iron 248.3 0.2 8.0 3.0 N2O–C2H2

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 3.1. Formulation studies

Emulsions are classified as oil-in-water emulsions (O/W) whenthe oils droplets are dispersed in an aqueous continuous externalphase; and water-in-oil emulsions (W/O) when the water dropletsare dispersed in an oily continuous external phase. Since the emul-

sions behave according to their external phase, for analytical pur-

poses, oil-in-water emulsions are the most appropriate optionsince they allow calibration with aqueous standards, besides pre-senting characteristics of long-term stability and low viscosity

(Remington, 1998).The hydrophilic-lipophilic balance (HLB) system for selecting

suitable emulsifiers to stabilize emulsions was developed by Grif-fin and it has been used for about five decades. According to the

Griffin scale, tensoactives with HLB values between 9.6 and 16.7are considered hydrophilic (water-soluble), and tend to form oil-in-water emulsions (Sinko, 2008). Non-ionic emulsifiers such as

Tween 80 and Triton X100 satisfy all requirements needed: theyhave ideal HLB values (13.5 and 15.0, respectively), they do nothave foaming properties, avoiding heterogeneous distribution of the oil drops in the emulsion (Sanz-Medel et al., 1999), and more-

over, they are inexpensive and readily available in most analyticallaboratories.

The oil/surfactant ratio was determined by experimental plan-ning. The combination of 4% emulsifier and 4% oil produced, for

sample amounts varying from 0.2% to 8%, emulsification withoutcoalescence. In all of the experiments in which the amount of oilwas smaller than the amount of emulsifier, the separation of phases took place immediately after preparation. This shows that

an excess of emulsifier in relation to oily phase favors emulsioninstability. Table 2 present the best formulation from the experi-mental planning and the metals that could be determined in eachformulation. The selection criteria are discussed in Section 3.3.

Despite the formulation stability and metal determinationcapability, it was necessary to analyze the level of contaminationby the metals studied in the oils and surfactants chosen. In our pre-

vious work, the oil and surfactant metal content was already deter-mined. Octyl stearate presented a relatively low contamination of all the metals investigated. Tween 80 presented high content of so-dium and Triton X100 high potassium and calcium content. Thus,for these elements, contamination limited the choice of surfactant

and oil (Ieggli et al., 2010).

 3.2. Formation and stabilization of the emulsion

Usually emulsions are prepared at temperatures between 70

and 80 C, and the aqueous phase is heated 5  C more than the oilyphase. However, in this work the best temperatures observed were65  C for Triton X100 and 75  C for Tween 80. Since the behavior of 

stable systems depends on the preparation conditions, care was ta-ken to assure that the procedure was carried out in exactly thesame way for all experiments. Phase inversion, which changesthe water-to-oil ratio by increasing the surfactant-water externalphase volume and correspondingly decreasing the internal phase

volume, provides a finely dispersed oil-in-water emulsion with

long-term stability (Lachman, Lieberman, & Kanig, 2001). In theinitial period of stirring the droplets necessary for the emulsifica-

tion are formed. If the stirring exceeds the necessary period forideal stability, adhesion can take place due to collision amongthe droplets. This period of time is usually determined empirically.In this study, the stipulated time was 2 min of manual mechanical

stirring to reach emulsification, followed by magnetic stirring at

3000 rpm for 15 min at room temperature for complete stabiliza-tion of the system.Creaming test may also be used to determine emulsion stability

(Mirhosseini, Tan, Hamid, Yusof, & Chern, 2009). The final appear-ance of all emulsions was from milky white to slightly brownand all chocolate emulsions presented relatively high values of ESI, since emulsion composition was previously optimized by

experimental planning. The octyl stearate/Tween 80/chocolatesample combination presented highest values of ESI (ESI1day =100%–ESI21days = 96.3%). The octyl stearate/Triton X100/chocolate

sample combination presented lower values of ESI (ESI1day =97.5%–ESI21days = 94.0%). The emulsions presented a precipitateafter 24 h. The precipitate was probably formed from the solid con-tent that was not stabilized by the micelles, however homogeneity

was re-established by shaking the mixture.

 3.3. Analytic applicability study and validation

Ideally, a single emulsion should be used for determination of all elements, however this was not possible mainly due to the pres-ence of the analytes as contaminants in both surfactants and oilycomponents (Ieggli et al., 2010) and due to different metal contents

in the samples. Based on these criteria, the metals that could beanalyzed in the same emulsion are shown in Table 2.

The characteristics of an analytical method are defined by thefigures of merit, which should be determined experimentally.

The proposed method was validated for six metals (Na, K, Ca, Mg,Zn and Fe). The figures of merit presented were linearity of the ana-

lytical curves, accuracy and precision. In addition, sensitivity wasdetermined by characteristic concentration (c 0).

Theadvantages of the emulsification procedure for fatty sampleshave been described in the literature. When properly stabilized, theemulsified sample is compatible with most analytical instruments,allowing the use of simple calibration procedures due to the mini-

mization of interferences (Sanz-Medel et al., 1999). In this study,calibration with aqueous standards was possible and the linearityranges were selected to span the metal concentrations expectedin real samples. Analytical curves were constructed by evaluatingthe relation between response (peak height and absorbance) and

concentration by linear regression analysis yielding the resultsshown in Table 3. In all instances, a linear fit was found to be ade-quate for the purpose.  Table 3 also presents the values found for

characteristic concentration for all elements.The accuracy of the method was further confirmed by deter-mining the metals in a baking chocolate CRM. The results areshown in  Table 4. Statistical comparison by means of the   t -testshowed that there was no significant difference between the val-

ues obtained with the proposed method and the certified values.

 Table 2

Chocolate and emulsion component amounts for metal determination by FAAS.

Element Chocolate sample amount (%) Emulsion components

White Milk Dark Oil phase % Surfactant %

Na 0.2 0.2 0.2 Octyl stearate 4.0 Triton X100 4.0

K, Ca, Mg 0.2 0.2 0.2 Octyl stearate 4.0 Tween 80 4.0

Fe 8.0 4.0 2.0 Octyl stearate 4.0 Triton X100 4.0

Zn 4.0 2.0 2.0 Octyl stearate 4.0 Tween 80 4.0

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The precisionof the procedures was determined through repeat-ability (intra-day precision). Six chocolate emulsions were assayed

during the sameday, underthe sameexperimental conditions. Inter-mediate precision(inter-day)was evaluated by assaying freshly pre-pared emulsions on three different days (n = 3). The repeatability

presented good relative standard deviation(RSD) values for all met-als. The intermediate precision was evaluated using the RSD and F -test. The computed  F -values were lower than tabulated  F -values,indicating no significant difference between the results obtained

on different days. All precision data are shown in Table 4.Although FAAS measurement of alkaline and alkaline earth met-

alsmayrequirethepresenceofanionizationbuffer(Welz& Sperling,1999) for the suppression of analyte ionization, in this study it was

not used. Probably, due to the nature of the matrices, no significantchanges were observed when the cesium/lanthanum chloride bufferwas used forthe measurementswith acetylene-nitrous oxide flame.

 3.4. Application to real samples

The proposed method was applied to evaluate Na, K, Ca, Mg, Zn,and Fe levels in different chocolate samples. We aimed to contrib-ute to provide a baseline of these elements in different kinds of 

chocolate (white, milk and dark). The analysis was carried out intriplicate and the results are shown in Table 5.

The mineral present in the highest concentration is potassium(K), with amounts varying from 2495 to 6361 lg g1. Interestingly,

the higher the cocoa content the higher the K level. The amount of sodium was found to be directly related to the content of milk andcocoa liqueur in the chocolates, however it also presented greatvariation among the brands. Chocolates contain amounts of cal-

cium varying from 324 to 4533 lg g1, where the highest levelsare in white chocolates. Chocolate contains levels from 365 to1834 lg g1 of Mg, for white and dark chocolate, respectively.

 Table 3

Regression parameters of the metal analytical curves.

Metal Rangea (mg L 1) Regression equationb R2 c 0 (mg L 1) LODc (mg L 1)

Potassium 1–10   A = 0.0619 + 0.1834C    0.9938 0.024 0.05Calcium 0.5–8   A = 0.0039 + 0.0996C    0.9994 0.044 0.16

Sodium 1–3   A = (0.0087 + 0.2839C )/(1 + 0.0558C ) 0.9951 0.015 0.02

Zinc 0.05–0.40   A = 0.0015 + 0.2312C    0.9958 0.018 0.02

Magnesium 0.5–4.0   A = (0.0124 + 0.2359C )/(1 + 0.1682C ) 0.9912 0.019 0.03

Iron 0.1–2.0   A = 0.0014 + 0.0228C    0.9977 0.191 0.02

a Five standard solutions each curve.b Absorbance, C  (mg L 1) = concentration of element in standard solution.c LOD = limit of detection.

 Table 4

Determination of the analytes in a certified reference baking chocolate (NIST SRM 2384).

Element Emulsion compounds Concentrations  lg g1 Recovery (%)   t expc Precision

Oil phase % Surfactant % Certified valuea Foundb Intra-day (RSD) Inter dayd (RSD/F expe)

Na Octyl stearate 4.0 Triton X100 4.0 40 ± 2 41 ± 2 103.0 0.04 3.8 1.0/0.34

K Octyl stearate 4.0 Tween 80 4.0 8200 ± 500 7266 ± 182 88.6 0.09 2.3 2.3/0.69

Ca Octyl stearate 4.0 Tween 80 4.0 840 ± 74 882 ± 11 105.0 0.04 1.0 0.3/0.14

Mg Octyl stearate 4.0 Tween 80 4.0 2570 ± 150 2600 ± 192 101.2 1.58 0.9 0.7/0.78

Fe Octyl stearate 4.0 Triton X100 4.0 132 ± 11 129 ± 11 97.5 0.01 4.6 2.6/0.55

Zn Octyl stearate 4.0 Tween 80 4.0 36.6 ± 1.7 38.6 ± 2.7 105.5 0.03 1.2 0.6/0.88

a With 95% confidence limit.b Mean value ± standard deviation (n = 3).c t tab = 2.31 ( p 0.05).d Time interval = 3 days.e F tab = 4.26 ( p  0.05).

 Table 5

Concentration levels of the elements (lg g1 ± SD,  n  = 3) in different chocolate samples.

Chocolate type Brand Cocoa content (%) Na K Ca Mg Fe Zn

White 1 n.i. 1033 ± 6 3069 ± 21 3990 ± 27 365.6 ± 1.6 1.2 ± 0.1 13.5 ± 0.32 n.i. 1121 ± 2 3474 ± 19 4096 ± 107 403.7 ± 1.8 1.3 ± 0.2 13.5 ± 0.0

3 27 1411 ± 7 3952 ± 26 4534 ± 92 496.8 ± 9.5 2.2 ± 0.1 13.4 ± 0.3

4 n.i. 921.0 ± 3 2840 ± 14 3404 ± 48 325.7 ± 2.5 1.7 ± 0.4 11.0 ± 0.1

5 n.i. 940.3 ± 1.4 2745 ± 14 3203 ± 57 334.2 ± 1.9 3.0 ± 0.2 10.3 ± 0.1

Milk 6 n.i. 515.2 ± 1.2 2661 ± 13 1813 ± 47 632.7 ± 6.5 16.5 ± 0.5 7.5 ± 0.1

7 n.i. 450.1 ± 7.2 2769 ± 32 1546 ± 11 736.6 ± 2.8 14.7 ± 0.7 7.7 ± 0.18 32 891.8 ± 3.8 3672 ± 8 2300 ± 18 867.2 ± 1.4 24.8 ± 0.7 9.4 ± 0.1

9 n.i. 530.8 ± 2.0 2596 ± 12 1744 ± 19 528.6 ± 36.5 27.4 ± 0.3 9.3 ± 0.1

10 n.i. 932.2 ± 4.4 3368 ± 4 2523 ± 33 714.3 ± 35.6 19.4 ± 0.2 10.7 ± 0.3

Dark 11 n.i. 500.3 ± 1.4 3654 ± 34 665.4 ± 31.3 997.3 ± 11.5 43.3 ± 0.6 12.4 ± 0.1

12 n.i. 127.7 ± 0.1 3849 ± 31 801.6 ± 3.0 1328 ± 15 36.1 ± 0.5 15.5 ± 0.113 43 59.8 ± 0.1 3718 ± 26 324.4 ± 24.0 1262 ± 7 64.6 ± 1.4 15.4 ± 0.1

14 n.i. 509.8 ± 2.5 3670 ± 11 730.7 ± 23.3 1036 ± 6 43.0 ± 0.5 12.1 ± 0.1

15 n.i. 93.1 ± 0.8 3746 ± 9 385.7 ± 12.3 1224 ± 2 35.8 ± 1.1 15.4 ± 0.0

16 50 496.2 ± 3.0 4932 ± 13 2069 ± 55 1576 ± 37 75.3 ± 1.5 15.8 ± 0.1

17 70 127.7 ± 0.6 6361 ± 34 692.4 ± 28 1834 ± 77 140.8 ± 7.7 23.3 ± 0.1

n.i.: Not informed.

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The minor component contents, Fe and Zn, ranged from 1.2 to140 lg g1 and from 8 to 23 lg g1, respectively. For both metals,the higher the cocoa content the higher the metal content.

4. Conclusion

It would ideal if a single emulsion could be used for the deter-

mination of all selected elements, however, this was not possibledue to the surfactant metal content and the different levels of eachmetal in the chocolate samples. The main advantages of the pro-posed method over traditional digestion methods are that it doesnot require a long sample treatment or large amounts of organic

solvents or inorganic acids and it is simple and shows good accu-racy and reproducibility. As the challenges and main requirementsfor emulsion application in atomic spectrometry involve theattainment of stable emulsions with low viscosity, the proposed

method including emulsification and subsequent metal determina-tion for FAAS fulfilled these requisites and proved to be sensitive,reproducible, simple, and economical.

 Acknowledgement

The authors thank CNPq (Conselho Nacional de Desenvolvimen-to Científico e Tecnológico) for scholarships.

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