124 Analyst, February, 1979, Vol. 104, $$. 124-135 Polarographic Determination of Trace Elements in Food from a Single Digest M. Kapel and M. E. Komaitis" Procter Department of Food Science, University of Leeds, Leeds, LS2 9JT The determination of 12 trace elements, namely copper, zinc, mercury, lead, cadmium, iron, tin, chromium, arsenic, antimony, selenium and tellurium, in admixture by means of a cathode-ray polarograph is described. The elements were investigated in concentrations ranging from 0.1 to 20 p.p.m. by means of normal, reverse-sweep or resistance - capacitance derivative techniques. The last technique could not be used for mercury, although it was used for all the other elements in concentrations less than 1 p.p.m. The complete determination took 4-7 h, and was applied to various kinds of food, such as bread, meat and vegetables. Keywords : Trace element determination; food analysis ; 9olarography ; single digest The determination of trace elements in food is of great importance, as some of them have nutritional significance, whilst others are toxic.The aim of this work was to establish a method that is accurate at an adequate level, is not very expensive, is rapid in comparison with other available techniques and covers a wide area of applicability. Solvent extraction has been used for a long time for the separation of trace elements. The technique is not characterised by specificity, a fact that can be turned to advantage when the method is combined with polarography. In the method recommended here, the sample is first digested with sulphuric and nitric acids and the pH then adjusted to a suitable value.Mercury(II), copper(II), zinc(II), cadmium(I1) and lead( 11) are removed in the form of dithizone (diphenylthiocarbazone) complexes.1 Concentrated hydrochloric acid is added to the aqueous phase, after which iron(II1) tin(1V) and antimony(III), if present, can be extracted in the form of salts of cupferron (ammonium N-nitrosophenylhydroxylamine) .2 The pH of the resulting aqueous phase is adjusted with ammonia solution, after which chromium(V1) is extracted with sodium diethyl- dithiocarbamate in chl~roform.~ The aqueous phase remaining is digested with sulphuric and nitric acids and, after complete destruction of the organic material, tellurium(IV), selenium(IV), antimony(V) and arsenic(II1) are determined.A flow diagram of the pro- cedure is shown in Fig. 1. Apparatus manufactured by Southern Analytical Limited. Corning Scientific Instruments. Reagents Experimental The work was carried out with an A 1660 Davis differential cathode-ray polarograph The pH was measured with a Digital 110 Expanded Scale pH meter manufactured by Nitric acid, concentrated relative density 1.42 (AnalaR) . Sulphuric acid, concentrated, relative density 1.84 (AnalaR) . Hydrochloric acid, concentrated, relative density 1.18 (AnalaR). Potassium hydroxide solution, 3 M. Ammonia solution, 6 M. Hydrochloric acid, 4 M. Sulphuric acid, 2 M. Dithizone solution. Cupfewon solzdion, 10% m/V. Prepared by solution of 50 mg of dithizone in 1 1 of chloroform. Prepared by solution of l o g of cupferron in 1 O O m l of distilled water.Greece. * Present address : Department of Food Chemistry, University of Athens, Navarinou 13, Athens( 144),KAPEL AND KOMAITlS 125 Dithizone in CHC13 pH 5.0-5.5 Sodium diethyldithiocarbamate solution, 5% m/V. diethyldithiocarbamate in 100 ml of distilled water. Ammorcium citrate solution, 20% m/V. Potassium iodide solution, 2% mlV. Potassiwn disulphite solution, 5% m/ V . Potassium chloride solution, 1 M. Hydrogefi peroxide, 30%. Ethyl acetate. Prepared by solution of 5 g of sodium r Zn(ll) Digest Sam p I e 10-159 - Dithizone in CHCl3 pH 8.5 Dithizone in CHCI:, pH 1.5-2.0 I Pb(ll), Cd(ll) I I CHC13 Aqueous solution A and ethyl acetate 1 Fe(lll), Sn(lV), Sb(lll) HCI or H2S04 + cupferron I Sodium diethyldithiocarbamate and CHC13 4 PH 4-6 Cr(VI) H Acid digestion Te(lV), Se(lV) KI + Kfi205 Fig. 1.Flow diagram of the procedure. Procedure The sample (10-15 g) was weighed accurately and transferred into a 600-ml Kjeldahl flask. Concentrated sulphuric acid (20-25 ml) and concentrated nitric acid (20-25 ml) were added and the mixture was heated in a fume cupboard (see Note 1). When the liquid turned brown, small amounts of concentrated nitric acid were added dropwise until complete decolorisation occurred. After decolorisation, heating was continued until the fumes of nitric acid had disappeared. This usually happened in 10-20 min according to the mass of sample. When the flask had cooled, the solution was transferred into a beaker with 40-50ml of water and 6 M ammonia solution was added, with stirring, until the pH value became 1.5-2.0.The solution was cooled and transferred into a 500-ml separating funnel, after which extrac- tion with 50-ml portions of dithizone in chloroform (extract 1) was used for the removal of126 KAPEL AND KOMAITIS : POLAROGRAPHIC DETERMINATION OF Analyst, Vol. 104 mercury(I1) and copper(I1). The extraction was continued until the organic layer did not change in colour. To the aqueous phase, 1 ml of 20% m/V ammonium citrate solution was added (see Note 2), the pH then being adjusted to between 5 and 5.5 with 6 M ammonia solution. The solution was transferred into a separating funnel and zinc(I1) was extracted with 50-ml portions of the solution of dithizone in chloroform (extract 2).Once again, the colour of the organic layer was used as the criterion for the completeness of the extraction. Subsequently, 1 ml of 20% m/V ammonium citrate solution was added and the pH was adjusted to 8.5 with 6 M ammonia solution. Lead(I1) and cadmium(I1) were then similarly extracted with dithizone in chloroform (extract 3). The chloroforni extracts, 1 and 2, were mixed and, after evaporation of the chloroform, digested with a concentrated nitric acid - sulphuric acid mixture (1 + 1). After cooling, dilution and adjustment to pH 5.0 with 6 M ammonia solution, mercury(II), copper(I1) and zinc(I1) were determined polarographically in 1 or 2 M ammonium sulphate solution. Alternatively, the digestion could be carried out with concentrated sulphuric acid and 30% hydrogen peroxide.For the determination of cadmium(I1) and lead(II), extract 3 was evaporated and the residue was digested with the nitric acid - sulphuric acid mixture (1 + 1) as above, after which the solution was diluted, and 1 M potassium chloride solution and 6 M ammonia solution were added until a solution 0.1 M in potassium chloride, 0.1 M in sulphuric acid and 0.8 M in ammonium sulphate was obtained with a pH of 1.6. This solution was then examined polarographically according to the details in the manufacturer’s manual. Once again, concentrated sulphuric acid and 30% hydrogen peroxide could be used as a digestion mixture. The chloroform extracts 1 , 2 and 3 were mixed and, after evaporation of the chloroform, digested with the concentrated nitric acid - sulphuric acid mixture (1 + 1).After cooling, dilution and adjustment to pH 5.0 with 6 M ammonia solution, mercury(II), copper(II), zinc(I1) and cadmium(I1) were determined polarographically in 1 or 2 M ammonium sulphate solution. For the determination of lead(I1) in a portion of the above solution, 1 M potassium chloride solution was added together with enough sulphuric acid to give a solution 0.1 M in potassium chloride, 0.1 M in sulphuric acid and 0.8 M in ammonium sulphate with a pH of 1.6. This solution was then examined polarographically for lead( 11). After the extraction of dithizonates, the aqueous phase was treated with either concentrated hydrochloric acid or concentrated sulphuric acid, so that the latter constituted 10% by volume of the resulting mixture.An excess of 10% w/V aqueous cupferron solution was added, after which iron(III), tin(1V) and antimony(II1) were extracted with two 50-ml portions of chloroform followed by similar portions of ethyl acetate (see Note 3). From the combined organic layers, the solvents were evaporated; then 25 ml of con- centrated nitric acid and 30ml of 30% hydrogen peroxide were added. The mixture was boiled until only a small volume remained. If a brown colour developed, a few drops of 30% hydrogen peroxide were added cautiously. The digestion was continued until the mixture became colourless. After the destruction of the organic material, 50 ml of 4 M hydrochloric acid were added and the solution was partly neutralised with 33.3 ml of 3 M potassium hydroxide solution.The mixture was transferred into a 100-ml calibrated flask and diluted to the mark with water, so that it became 1 M in potassium chloride and 1 M in hydrochloric acid. This solution was examined polarographically. The acidic aqueous phase remaining after the extraction of the cupferronates was adjusted with 6 M ammonia solution to a pH of 4-6, and an excess of 5% m/V aqueous sodium diethyl- dithiocarbamate solution was added. The mixture was shaken and chromium(V1) was extracted with several 50-ml portions of chloroform until the aqueous layer was clear and colourless. The organic layer was digested with concentrated nitric acid and 30% hydrogen peroxide in the manner described above. Twenty-five millilitres of 4~ hydrochloric acid were added, and the mixture was neutralised with 3~ potassium hydroxide solution.It was then transferred into a 100-ml calibrated flask and diluted to the mark with water, so that it became 1 M with respect to potassium chloride. This solution was investigated polaro- graphically, the peak potential, E,, being -1.25 V. Hence, all metals forming dithizonates were removed from the solution. Alternatively, the determination could be carried out as follows.Februayy, 1979 127 Alternatively, a mixture of concentrated nitric and sulphuric acids in equal proportions by volume could be used. In this instance, the neutralisation was carried out with 6~ ammonia solution and the solution was diluted until it became 1-2 M with respect to ammonium sulphate. The aqueous phase remaining from the extraction of chromium was evaporated to a small volume and then digested with a concentrated nitric acid - sulphuric acid mixture (1 + 1).After this digestion, a convenient amount (10-50 m1) of hydrochloric acid (1 + 1) was added and the solution was split into two portions of equal volume. The first of these portions was evaporated until fumes appeared, cooled, diluted and neutralised with 6~ ammonia solution to pH 8.5. It was then suitably diluted to yield a solution 1 M with respect to ammonium sulphate. Tellurium(1V) and selenium(1V) were determined polarographically in this mixture. To the second portion, 2% m/V potassium iodide and 5% m/V potassium disulphite solutions were added in excess and the mixture was heated until white fumes appeared. The flask was cooled and the solution, suitably diluted to a known volume, was divided into two equal parts. To the first part, distilled water was added until the solution was 1 M in sulphuric acid.The second part was diluted and neutralised with 6~ ammonia solution to pH 8.5. After suitable dilution, antimony (111), originally present as antimony(V) , was determined polarographically in a solution 1 M in ammonia and 1 M in ammonium sulphate. TRACE ELEMENTS I N FOOD FROM A SINGLE DIGEST Arsenic( 111) was then determined polarographically. NOTES- solution is recommended. of some metals. tin(1V) a t high pH. ammonium citrate solution. not be achieved with chloroform alone. 1. 2. In the presence of chromium(III), the addition of 2 ml of 3% m/V ammonium peroxodisulphate The addition of 20% m/V ammonium citrate solution was necessary to prevent the precipitation Ammonium oxalate solution was also tried, but was not effective in the presence of It was found that the extraction of tin(1V) was unaffected by the presence of The use of ethyl acetate for the extraction of tin(1V) was necessary, as a complete recovery could 3.Results A sample solution containing all the elements under consideration was digested according to the method described above. The solution was diluted to 1 1, and the method was applied to 10 ml of the diluted solution. The determination was carried out twice, and the results are shown in Table I. TABLE I DETERMINATION OF ELEMENTS IN ADMIXTURE Peak height, scale divisions Concentra- Peak r h \ Metal ion tion, p.p.m. Supporting electrolyte potential/V Found Theoretical Recovery, % Cu(I1) Hg(W Zn(I1) Pb(I1) Cd(I1) Fe(II1) Sn(1V) Cr(V1) As(1II) Se(1V) Sb(II1) Te( IV) ..7.21 . . 16.69 . . 15.82 , . 10.26 . . 11.37 . . 11.20 . . 9.47 . . 15.64 . . 9.23 .. 17.44 .. 10.00 . . 13.07 0.8 M 0.8 M - 0.23 -0.05 -1.30 - 0.52 - 0.73 -1.05 -0.60 - 1.85 -0.75* -1.50 - 0.617 1.10, 1.00 1.10, 1.05 2.60, 2.60 1.10.1.10 1.65: 1.65 1.16, 1.00 0.55, 0.52 2.50, 2.50 14.20, 14.00 0.60, 0.60 2.20; 2.00 3.75, 3.80 1 1.10 1.16 2.63 1.80 1.70 ~. . 1.07 0.50 2.50 15.00 0.60 2.20 4.00 100.00, 90.91 95.65, 91.30 98.86, 98.86 61.10, 61.10 97.06, 97.06 10841 9346 110’00’ 1ok 00 100:oo: 100:00 100.00, 100.00 100.00, 90.91 93.75, 95.00 94.67, 93.33 * Resistance - capacitance derivative circuit used. t Tellurium(1V) was determined by means of the peak at -1.04 V.In the determination of antimony(II1) a correction was made for the ovedapping tellurium peak. From this table, it can be seen that all the elements can be determined accurately with recoveries ranging from 90.9 to lOOyo, except for lead(II), where the recovery was 55.565!40. This discrepancy was due to the fact that some lead(I1) was lost by precipitation in the form of sulphate. Lead must be present at a concentration less than 7 p.p.m. in order to prevent this loss.TABLE I1 DETERMINATION OF THE ELEMENTS IN BEEF SAUSAGE WITH PORK Concentration, Concentration, Concentration, Concentration, Concentration, p.p.m.* p.p.ni.* p.p.m.* p.p.m.* p.p.m.* ion Cr(V1) Fe (111) Pb(I1) Cd(I1) Sn(IV) HdII) Cu(I1) Zn(I1) As (I1 I) Sb(II1) WIV) SelIV) Ft 20.93 13.40 14.98 9.08 13.54s 14.08 21.50 8.99 19.74 12.39: 12.89: 15.28 25.28t Et 20.15 12.20 14.42 13.22 14.64 21.50 9.28 20.38 11.88 12.89 16.84 22.47 Ft 12.13: 6.78 8.041 7.58 5.668 8.47: 7.97: 5.37: 14.20 5.86s 11.49: 11.35 6.32: 6.09: 8.28 8.85$7 9.49$ 12.99 Et 11.65 7.05 8.34 7.64 8.47 12.43 5.37 11.79 6.87 7.45 9.74 11.99 .r 12.35: * The concentrations are expressed in p.p.m. of sample mass. t F = found; E = expected. : Resistance - capacitance derivative circuit was used. 5 Reverse voltage was used. T[ Calculated a t different values of E, (peak potential). Ft 16.96: 18.96 10.30 13.58: 8.60: 12.875 12.06 17.80 8.15s 8.55: 17.25: 17.47; 9.81:. 11.28: 13.62; 20.32; Et 17.70 10.72 12.67 11.61 12.87 18.88 8.15 17.91 10.44 11.32 14.79 19.74 Ft 3.65: 3.55 4.35: 4.03: 4.10: 5.95 2.90; 6.15; 3.42; 4.151 4.75: 6.40; 6.10 3.70 4.35 4.00 4.35 6.50 2.80 6.15 3.60 3.80 5.10 6.80 5.80 3.50 4.15: 4.065: 4.50: 6.25 3.00: 6.65: 3.52$ 4.101 4.853: 6.45: Et 6.25 3.80 4.40 4.10 4.60 6.65 2.90 6.33 3.70 4.00 5.12 6.95 Ft 1.09: 0.57 0.83: 0.67: 0.74: 1.03 0.54: 1.16: 0.72: 0.59: 0.90: 1.22: Et 1.02 0.62 0.73 0.67 0.74 1.09 0.47 1.03 0.65 0.65 0.86 1.14 Concentration, Concentration, Concentration, p.p.m.* p.p.m.* p.p.m.* -7 & Ft 1.04: 0.70; 0.77: 0.76: 0.881 1.47 0.56: 1.37 0.63: 0.73; 1.07; 1.24: Et 1.21 0.73 0.86 0.79 0.88 1.29 0.56 1.22 0.71 0.77 1.01 1.34 Ft 1.11: 0.80: 0.68: 0.76; 0.87: 1.46 0.52: 1.29: 0.63: 0.70; 1.10: 1.26: Et 1.20 0.72 0.86 0.78 0.87 1.28 0.55 1.22 0.71 0.77 1.00 1.34TABLE I11 DETERMINATION OF THE ELEMENTS IN BEEF Metal ion Cr(V1) Sn(1V) Fe(II1) Pb(I1) Cd(I1) Hg(I1) Cu(I1) Zn(I1) As( 111) Sb (I I I) Te(1V) Se(1V) Concentration, p.p.m.* - Ft Et 12.64 11.96 11.061 6.54 7.24 7.37 8.11 5.81: 7.84 8.69: 8.69 7.905 10.93 12.76 5.85; 5.51 5.61s 12.55; 12.10 12.32 7.2817 7.05 6.651 8.50 7.65 10.65 9.94 13.88 13.33 8.88: Concentration, p.p.m.* * Ft Et 13.57jV 15.27 13.261 9.77 9.25 10.541 10.93 11.13 10.09g 12.68:: 15.13 7.36s 7.481 14.00: 14.75 9.01:v 8.861 11.63 15.19 20.43: 15.76 10.02 11.10 16.29 7.04 15.45 9.01 9.77 12.76 17.03 Concentration, p.p.m.* * Ft Et 10.0517 10.49 9.83 5.80 6.35 6.23 7.51 8.23; 4.59: 6.88 6.93s 7.62 7.84: 12.42 11.19 4.83s 4.83 Footnotes as in Table 11.Concentration, p.p.m.* - I Ft Et 5.55: 5.90 3.40 3.60 4.051 4.20 3.851 3.85 4.20: 4.20 5.95 6.30 2.60: 2.70 Concentration, p.p.m.* - Ft Et 6.10: 6.50 3.80 3.95 4.65: 4.675 4.25: 4.30 4.702 4.75 6.75 6.95 2.90: 3.00 Concentration, p.p.m.* -7 I.'t Et 1.68: 1.57 1.78 0.88 0.95 1.19: 1.12 0.84 1.03 1.231 1.14 1.20 2.14 1.67 0.72: 0.72 5.11 10.20 10.61 5.951 5.95 6.90: 6.60 1.49: 1.59 9.61; 6.70 6.19 3.10: 3.45 3.65: 3.85 1.02: 0.93 6.68: 8.04 6.71 3.50: 3.75 3.93: 4.17 1.091 1.00 9.97 8.77 6.20: 6.55 6.90; 7.30 1.471 1.31 13.19 11.69 4.75: 4.90 5.40: 5.45 1.63: 1.76 12.12; Concentration, p.p.m.* * Ft Et 0.97: 1.09 0.60 0.65 0.73: 0.78 0.68: 0.71 0.77: 0.79 1.09 1.16 0.50: 0.50 1.14: 1.10 0.601 0.64 0.64: 0.69 0.83: 0.91 1.21: 1.21 Concentration, p.p.m.* r--J--7 Ft Et 1.082 1.12 0.64 0.68 0.77: 0.80 0.701 0.73 0.81: 0.81 1.08 1.19 0.49: 0.52 1.18: 1.13 0.66: 0.66 0.64: 0.72 0.86; 0.94 1.17: 1.25w 0 TABLE I V DETERMINATION OF THE ELEMENTS IN PORK LUNCHEON MEAT Metal ion Cr(V1) Sn(1V) Fe(II1) Pb(I1) Cd(I1) Hg (11) Cu(I1) Zn(I1) As ( 111) Sb ( I I I) Te (IV) Se(1V) Concentration, p.p.m.* * Ft Et 12.02 11.54 12.02; 6.72 6.99 5.85: 8.26 5.60: 7.54 7.70: 8.39 8.399 11.25 12.31 5.06: 5.32 19.11 11.68 12.55: 6.48'; 6.81 7.139 7.38 9.12:fi 9.65 8.69: 13.42 12.87 12.42: Concentration, p.p.m.* - Ft Et 12.30 12.73 12.30: 7.41 7.71 9.76: 9.11 9.11 6.19 8.35 9.25 9.25 9.253 12.80 13.58 5.54 5.86 5.863 13.58 12.88 13.63: 7.26; 7.51 7.73: 8.14 9.80 10.64 15.96 14.19 14.94: t Concentration, p.p.m.* F r Ft Et 12.998 13.65 7.95 8.27 8.88 9.77 9.63 : 6.63 8.95 9.03: 13.32 14.57 6.86 6.29 6.29: 14.67 13.81 14.32: 7.89: 8.05 7.94: 8.73 10.38: 11.42 11.421 16.90 15.22 17.90: 9.939 9.93 Footnotes as in Table 11.Concentration, p.p.m.* - Ft Et 5.85; 5.45 3.15 3.30 3.80$ 3.90 3.45: 3.60 3.95; 3.95 6.00 5.85 2.455 2.50 5.953 5.55 3.20: 3.20 3.30; 3.50 4.30; 4.60 6.25: 6.10 I Concentration, p.p.m.* ----h--7 Ft Et 5.45$ 5.60 3.10 3.32 3.85: 4.00 3.50: 3.65 4.00: 4.05 6.10 5.95 2.55: 2.55 5.93: 5.75 3.15: 3.30 3.38; 3.60 4.25: 4.60 6.20; 6.20 f Concentration, p.p.m.* - Ft Et 1.01: 1.09 0.63 0.66 0.651 0.78 0.72; 0.72 0.77: 0.79 1.08 1.16 0.54: 0.50 1.17: 1.10 0.60: 0.64 0.76: 0.70 0.91: 0.91 1.31: 1.22 Concentration, p.p.m.* b r Ft Et 0.91: 0.98 0.54 0.59 0.65: 0.70 0.61: 0.64 0.71; 0.71 0.96 1.05 0.42: 0.45 0.99: 0.99 0.521 0.58 0.59: 0.63 0.96: 0.82 1.23: 1.09 * Z U Concentration, t, 1;; z p.p.m.* 0, Ft Et 0.87: 0.94 N 0.56 0.57 8 0.65: 0.67 W 0.61: 0.61 % 0.68: 0.68 U 0.94 1.00 0.43; 0.43 kl 0.93; 0.95 Z 0.65: 0.56 * 0.57; 0.60 8 0.86; 0.78 Z 0 1.08: 1.04 bTABLE V c3 w * 0 M Concentration, Concentration, Concentration, Concentration, Concentration, Concentration, Concentration, Concentration, M r p.p.m.* p.p.m.* p.p.m.* p.p.m.* p.p.m. * p.p.m.* p.p.m.* p.p.m.* M DETERMINATION OF THE ELEMENTS I N BREAD Footnotes as in Table 11.Metal - - & & & & & & Et Ft Et Ff Et Ft Et Ft Et F1. Et Ft Et ion Ft Cr(V1) 14.67$T[ 14.67: Sn(1V) 7.75 Fe(II1) 10.06: Pb(I1) 5.24 Cd(I1) 10.67: Hg(I1) 15.78 6.46 Zn(I1) 12.50 13.183 As(II1) 7.34: Sb(II1) 9.20 8.07 Te(1V) 12.811 10.40 Se(1V) 14.38 cqIq 5.86: .. Et Ft 13.57 13.74 13.74: 8.22 9.77 9.72 11.10: 8.90 7.18: 9.87 10.835 10.03 14.48 18.27 6.10 16.24 9.72 6.25 7.203 13.73 14.405 8.01 8.25: 8.68 10.46; 11.35 14.32 11.27; 15.14 19.65: 14.99 9.07 10.73 9.83 10.89 15.99 6.90 15.16 8.84 9.59 12.53 16.71 13.57 15.42'; 8.11 9.64 11.61: 7.20: 10.77: 18.40 7.67: 6.945 15.55: 15.26 9.02: 8.25: 9.795 10.53 13.26 17.20 14.81 8.97 10.60 9.72 10.77 15.80 6.82 14.99 8.74 9.48 12.38 16.52 7.35: 5.25 5.90: 5.10; 5.80: 7.60 3.40: 3.495 7.55s 7.45: 4.50: 5.30: 6.20: 9.45: 7.80 7.30: 4.70 5.10 5.55 5.95: 5.10 4.95: 5.65 5.65: 8.30 7.90 3.60 3.40 7.85 7.95: 4.60 4.55: 4.98 5.12$ 6.50 5.95f 8.70 10.00: 7.85 4.75 5.60 5.15 5.70 8.40 3.60 7.95 4.65 5.00 6.55 9.25 1.02: 0.56 0.629 0.61: 0.68: 0.69: 1.16 0.41 : 0.90: 0.53: 0.62: 0.90: 1.06: 0.95 0.58 0.68 0.63 0.69 1.02 0.44 0.96 0.56 0.61 0.80 1.06 1.16: 0.79 0.86: 0.84: 0.922 1.36 0.7 1 : 1.28: 0.79: 0.80: 1.12; 1.68: 1.35 0.82 0.96 0.88 0.98 1.44 0.62 1.36 0.79 0.86 1.12 1.50 1.191 0.776 0.92: 0.87: 0.97: 1.40 0.641 1.41: 0.76; 0.82: 1.06: 1.55: 1.39 2 0.84 z 0 0.91 u Y 0.99 2 1.01 3 1.48 0.64 + 1.41 $ s 0.82 pj U 0.89 ij 1.16 5 1.55TABLE VI DETERMINATION OF THE ELEMENTS IN MIXED VEGETABLES Metal ion Cr(V1) Sn(1V) Fe (111) Pb(I1) Cd(I1) Hg(I1) Cu(I1) Zn(I1) As(II1) Sb (I I I) Te (IV) Se(1V) Concentration, p.p.m.* * Ft Et 7.11 7.11 6.807 6.80: 3.91 4.30 4.855 5.09 4.63: 3.58: 4.66 5.17: 5.17 4.765 4.71 8.55 7.58 2.975 3.27 3.84 7.525 7.19 6.361 4.11: 4.19 5.15 4.55 5.54 5.94 8.325 7.92 7.60: Footnotes as in Table 11.Concentration, Concentration, Concentration, Concentration, Concentration, p.p.m.* p.p.m.* p.p.m.* p.p.m.* p.p.m.* - - - - r - - - - - l Ft Et Ft Et Ft Et Ft Et Ft Et 19.73: 21.14 22.39 20.15 4.20: 4.50 4.25: 4.40 0.75$ 0.88 19.37:7 18.42: 12.30 14.40s 13.75: 9.70: 14.15 13.965 15.36: 20.94 9.83': 8.855 20.23 12.79 11.09 12.20 2.55 2.75 2.55 2.65 0.55 0.53 15.13 13.11: 14.42 3.05: 3.25 2.96: 3.15 0.59; 0.63 13.86 9.25: 13.22 2.85$ 2.95 5.75: 5.77 0.53: 0.58 15.36 15.42 14.65 3.30: 3.30 3.15: 3.20 0.64: 0.64 22.55 24.26 21.50 4.95 4.83 4.85 4.70 0.94 0.94 9.74 8.62 9.28 1.90: 2.10 1.80: 2.00 0.44: 0.41 21.38 18.54 20.39 4.851 4.60 4.45: 4.45 0.83: 0.89 13.36: 13.301 12.47 11.89 11.89 2.40; 2.60 2.45: 2.60 0.52: 0.52 14.02 13.52 12.89 12.89 2.60: 2.90 2.651 2.80 0.53: 0.56 19.63 17.67 16.84: 16.84 3.80: 3.80 3.55; 3.65 0.92$ 0.98 21.63; 23.67 22.6317 23.57 23.97: 22.47 4.75: 5.05 4.65: 4.90 0.79: 0.74 Concentration, p.p.m.* - 0.69: 0.77 Ft Et 0.43 0.46 0.53: 0.55 0.48: 0.50 0.60: 0.57 0.75 0.82 0.33: 0.35 0.77: 0.77 0.47; 0.45 0.45: 0.49 0.59: 0.68 0.75 0.85 * Z U Concentration, !$ Ft Et ..p.p.m.* k (------A---72 0.66: 0.71 5: w 0.41 0.43 0 0.49: 0.51 8 0.45: 0.47 ' 0.54: 0.52 $ U 0.69 0.76 3 0.31: 0.33 pj 0.75: 0.72 z 0.44: 0.42 5 0.43: 0.49 z 0.75: 0.80 V 5 5 0.56: 0.60 0TABLE VII DETERMINATION OF THE ELEMENTS IN JELLY Footnotes as in Table 11. Concentration, p.p.m.* Metal ( - A - , ion Cr(V1) Sn(1V) Fe (I1 I) Pb(I1) Cd(I1) 2(Y# Zn(I1) As (I 11) Sb(II1) Te(1V) Se(1V) Ft Et 7.987 8.78 4.81 5.32 6.29: 6.29 4.43: 5.76 4.03 6.19: 6.38 5,805 7.36 9.37 3.69 4.05 8.545 8.88 9.43 5.54 5.18 6.31 5.62 6.857 7.34 7.01 9.367 9.79 9.41 10.11: Concentration, p.p.m.* * Ft Et 10.94 10.50 5.87 6.36 6.71: 7.52 4.77 6.89 7.21s 8.03: 9.60 4.60: 5.22 11.39 6.93: 7.63 7.98:7 7.90: 11.36: 11.71 11.12: 7.63 11.21 4.84 10.63 6.19 6.72 8.78 11.71 Concentration, Concentration, Concentration, Concentration, p.p.m.* p.p.m.* p.p.m.* p.p.m.* ---- Ft Et Ft Et Ft Et Ft Et 13.25: 12.72 4.05: 4.30 4.10: 4.40 1.93: 2.075 13.25 7.40 7.70 2.45 2.60 2.47 2.65 1.33 1.26 8.28 9.11 2.70; 3.05 2.90: 3.15 1.38: 1.48 9.76: 6.49: 8.34 2.66: 2.65 2.875: 2.90 1.41: 1.36 8.43: 9.25 3.025: 3.10 3.15: 3.20 1.42: 1.51 8.41s 15.50 13.57 4.30 4.60 4.45 4.70 2.52 2.21 6.08: 5.86 1.90: 1.97 2.00: 2.05 1.03: 0.96 5.865 12.06; 12.87 4.50; 4.35 4.45: 4.45 2.23: 2.10 12.16 7.20: 7.50 2.55: 2.55 2.85: 2.60 1.15: 1.22 7.40 8.14 2.50: 2.75 2.65; 2.80 1.21: 1.33 9.30S7 10.63 3.25: 3.50 3.50: 3.70 1.64: 1.73 9.30: 16.36 14.18 4.30: 4.80 4.601 4.90 2.38: 2.31 16.68: Concentration, p,p.m.* * Ft Et 0.78: 0.88 0.49 0.54 0.65: 0.63 0.56; 0.58 0.68: 0.64 0.89 0.94 0.41: 0.41 0.98: 0.89 0.51: 0.52 0.52: 0.56 0.68: 0.74 1.10: 0.98 Concentration, p.p.m.* * Ft Et 0.85: 0.92 0.62 0.56 0.64: 0.66 0.58: 0.60 0.67: 0.67 0.98 0.98 0.42: 0.42 0.97: 0.93 0.53: 0.54 0.66: 0.59 0.71: 0.77 1.03: 1.03 c1 w w134 Analyst, Vo,?.I04 For this purpose, a portion of food (10-20 g) was weighed accurately, and known amounts of the elements concerned were added. After treatment in accordance with the method described above, the metals were determined polarographically.The foods used were beef sausage with pork, fresh meat (beef), pork luncheon meat, bread, mixed vegetables, jelly, orange and lemon drink. The results are shown in Tables 11, 111, IV, V, VI, VII and VIII, respectively. KAPEL AND KOMAITIS : POLAROGRAPHIC DETERMINATION OF The method was applied to various kinds of food. TABLE VIII DETERMINATION OF THE ELEMENTS I N ORANGE - LEMON DRINK Footnotes as in Table 11. Metal ion Cr(V1) .. . . Sn(1V) . . .. Fe(II1). . .. Pb(I1) . . .. Cd(I1) . . .. Hg(I1) .. .. Cu(I1) . . .. Zn(I1) . . .. As(II1). . . . Sb(III).. .. Te(1V) .. .. Se(1V) .. .. Concentration, p.p.m.* * =t Et 0.17: 0.16 0.10 0.10 0.11: 0.11 0.09; 0.10 0.11: 0.11 0.18 0.17 0.08: 0.07 0.15: 0.16 0.10: 0.09 0.11 0.10 0.12: 0.13 0.15 0.17 Concentration, p.p.m.* F f.Et ' 0.86: 0.78 0.49 0.47 0.55: 0.56 0.49: 0.51 0.57: 0.57 0.855 0.83 0.37: 0.36 0.72: 0.78 0.47: 0.46 0.52: 0.50 0.62: 0.65 0.83: 0.87 Concentration, p.p.m.* - Ft Et 0.15: 0.16 0.09 0.10 0.12; 0.11 0.10: 0.10 0.11: 0.11 0.18 0.17 0.07: 0.07 0.17: 0.16 0.09: 0.09 0.09$ 0.10 0.14: 0.13 0.18: 0.17 Discussion The elements were investigated in a range of concentrations varying from 21 to 0.1 p.p.m. Mercury( 11) was determined by the normal polarographic process, because the mercury peak is in the region of zero voltage and the resistance - capacitance derivative circuit does not give accurate results. Tin(1V) was also determined by the normal process. The elements most accurately determined were cadmium(II), lead(I1) (for concentrations less than 7 p.p.m.), antimony(III), arsenic(III), zinc(I1) and tellurium(1V).Copper(I1) was determined with less accuracy, whilst chromium(VI), selenium(IV), iron(III), mercury(I1) and tin(1V) gave results which were even less accurate. The errors in the determinations of chromium(VI), selenium(IV), iron(II1) and tellurium(1V) could be attributed in part to the fact that the peaks of these elements were close to the hydrogen peak, with which they partly overlapped. Mercury(I1) gave a peak near the point of zero voltage (E, = -0.05 to -0.07 V) and, because of this, it could not be deter- mined accurately. The same was true of copper(I1) ( E , = -0.20 V), although to a lesser degree. The time required for the complete analysis varied from 4 to 7 h, according to the con- centrations of the elements. The reason for this was that the time required for the extraction of copper(II), mercury(II), lead(II), zinc(I1) and cadmium(I1) with dithizone increased considerably when the concentrations were greater than 10 p.p.m. The use of the resistance - capacitance derivative graph was necessary for most of the elements at concentrations below 1.2 p.p.m. Conclusion The procedure possesses considerable advantages of time and cost over most other methods designed for the simultaneous determination of 12 elements.February, 1979 TRACE ELEMENTS I N FOOD FROM A SINGLE DIGEST 135 Our thanks are due to Professor D. S. Robinson and Professor A. G. Ward for their interest and encouragement and to J. Sainsbury Limited for financial support. One of us (M.E.K.) thanks Professor D. S. Galanos of the University of Athens for his encouragement, the Greek State Scholarship Foundation for a maintenance grant and the University of Athens for leave of absence. References 1. 2. 3. Fischer, H., Angew. Chew., 1937, 50, 919. Baudisch, O., Chemikerzeitung, 1909, 33, 1298. Lacoste, R. J., Earing, M. H., and Wiberly, S. E., Analyt. Chew., 1951, 23, 871. Received March 3rd, 1978 Accepted Augu.st 23rd, 1978