596 Analyst, August, 1973, Vol. 98, p p . 596-604 The Determination of Lead in Foods by Atomic-absorption Spectrophotometry BY R. K. ROSCHNIK (Nestle' Products Technical Assistame Co. Ltd., Control Laboratory, Case Postale 88, Ch-1814 L a Tour-de-Peilz, Switzerland) Rapid procedures for the determination of lead in foods by an organic extraction technique and atomic-absorption spectrophotometry are described. The food sample can be dry ashed or digested by using sulphuric acid and hydrogen peroxide. In the latter instance, digestion need not be complete. Lead is extracted from acidic solutions (either the dissolved ashes or the residual solution after acid digestion) into xylene as its diethylammonium diethyldithiocarbamate chelate, and then determined by use of atomic- absorption spectrophotometry.Large amounts of iron and tin do not interfere in the determination. In a 10-g sample, 0.02 p.p.m. of lead can be detected. The standard deviation in the range from 0.2 to 1.0 p.p.m. of lead is about 0.02 p.p.m. Certain products do not require preliminary diges- tion; in these instances lead is extracted directly from the acidified sample. Liquids, beverages and many canned foods can be monitored very rapidly in this way. The chelate - solvent combination used in this method is more convenient than the ammonium tetramethylenedithiocarbamate - isobutyl methyl ketone system. The method is applicable also to metals other than lead; its use for cadmium has been demonstrated successfully. LEAD has attracted considerable attention as a public health hazard and legal limits for its occurrence in foods have been set, or proposed, from 0-3 to 8 ~ .p . m . l - ~ Normal levels found in foods range from 0.1 to 5 ~ . p . m , ~ - ~ Contamination during and after processing, notably from containers (cans or glazed earthenware), has been the subject of several ~tudies,~s*-l~ but it is hardly a major hazard today. The most important source of lead contamination of foods would appear to be motor-vehicle exhaust f ~ m e s , ~ , ~ lead being deposited on the leaves of plants. Lead thus enters foods either directly (with fruit and vegetables), or indirectly, through feedstuffs into meat and milk products.ll Atmospheric industrial fall-out may also be of importance in certain localities. The monitoring of lead in foods is therefore important.The determination of lead in foods usually requires preliminary destruction or degradation of the organic matter. During dry ashing there is a slight risk of loss of lead by volatilisation of its halides, but this can be eliminated by the addition of sulphuric acid before ashing.12 The temperature must, however, be kept below 500 *C.13 Ashing aids such as magnesium nitrate14 and aluminium and calcium nitrates13 have been used. For canned and liquid products wet ashing is usually the more rapid procedure. The use of sulphuric acid is not always advantageous as precipitating alkaline earth sulphates may remove much of the lead sulphate by adsorption. However, this very phenomenon forms the basis of a method for lead determination.l5Yl6 The determination of lead by atomic-absorption spectrophotometry is not a very sensitive method, so that special measures usually need to be taken to improve the detection limit in food.Background absorption problems become acute in the presence of large amounts of salts, especially at the more sensitive wavelength of 217.0 nm. The aspiration of aqueous solutions after ashing usually requires some form of background correction, either by use of non-absorbing lines5 or by using a continuum background.17 Flameless techniques can result in improved sensitivity but cannot eliminate salt effects so that background correction becomes essential if they are used. Use of the device of organic extraction avoids most of the background problems in this instance, and also increases the sensitivity. At present only the ammonium tetramethylene- dithiocarbamate - isobutyl methyl ketone system appears to have been used for the deter- mination of lead in foods by atomic-absorption ~pectrophotornetry.~J~-~~ The present paper @ SAC and the author.ROSCHNIK 597 presents a very useful organic extraction technique that makes use of the diethylammonium diethyldithiocarbamate - xylene system first described by Jordan.22 Problems of pH adjust- ment do not arise with this technique, and in favourable instances the determination can be carried out without preliminary ashing of the product.EXPERIMENTAL REAGENTS AND APPARATUS- Normal precautions for trace analysis were taken throughout. Analytical-reagent grade reagents were used, except for the xylene, which was of laboratory reagent grade.No attempt was made to purify the reagents further. Standard lead solutions were prepared from lead nitrate, the working standard containing 10 p.p.m. of lead in 1 per cent. V/V nitric acid. Standard tin( 11) solutions were prepared by dissolving tin in concentrated hydrochloric acid (then diluting to 10 per cent. V/V of acid in each instance) and standard tin(1V) solutions by dissolving tin in hot, concentrated sulphuric acid (then diluting to 20 per cent. V/V of acid in each instance). Standard iron(I1) solutions were prepared from iron(I1) sulphate and pre- served in dilute sulphuric acid, while standard solutions of the iron(II1) ion were prepared from iron( 111) chloride, standardised and preserved in hydrochloric acid.A Perkin-Elmer 303 atomic-absorption spectrophotometer, fitted with a Hitachi recorder, an ordinary lead hollow-cathode lamp and a three-slot burner head, was used for atomic- absorption measurements. When solutions in xylene were aspirated, the instrument settings were as shown in Table I. A Beckman DB spectrophotometer was used for colorimetric determinations. TABLE I OPERATING CONDITIONS FOR PERKIN-ELMER 303 ATOMIC-ABSORPTION SPECTROPHOTOMETER WHEN ASPIRATING XYLENE SOLUTIONS CONTAINING LEAD Wavelength . . .. 283.3nm Scale expansion . . x 1 Lamp current .. 30mA Damping setting . . 2 Slit setting . . .. 4 Working range . . 1 to 10 p.p.m. Air pressure . . . . 30 p s i . ; flow setting 8.5 Acetylene pressure . . 8 p.s.i. ; flow setting 1.5 Food samples were obtained from local shops.In addition, a number of long-term storage samples of canned and bottled foods from various parts of the world were available to us and included in the study. Some of the older canned products were left in the can for several days after opening in order to increase their lead and tin contents. METHOD A (DRY ASHING)- Add 5ml of 20 per cent. sulphuric acid to a 5 or 10-g (homogenised) food sample in a silica crucible. (The sulphuric acid can be omitted if it has been confirmed that, after dry ashing, the recovery of added lead is 100 per cent. for the product in question.) Evaporate the contents to dryness and start to ash the residue over a small flame. Then, complete the ashing in a furnace at 500 "C for 3 to 18 hours, according to the product.If an appreciable amount of carbon remains after 18 hours, allow the crucible to cool, then moisten the ash with a few drops of 50 per cent. magnesium nitrate solution. Evaporate to dryness slowly and re-ash at 500 "C for a further hour. Moisten the cold ash with a small volume of water, then add 5 ml of 6 N hydrochloric acid. Warm the mixture on a boiling water bath to complete dissolution and transfer it quantitatively to a 50-ml calibrated flask. Dilute with water to about 25 ml, cool and add 5 ml of xylene containing 1 per cent. of diethylammonium diethyldithiocarbamate. Stopper the flask and shake it vigorously for 40 to 60 s, allow the phases to separate and add water to bring the organic phase into the neck of the flask. Finally, aspirate the organic phase into the atomic-absorption instrument, under the conditions given in Table I.A calibration chart is prepared by introducing 0, 10, 20, 30 and 40 pg of lead into a series of 50-ml flasks. To the lead solution add 5 ml of 6 N hydrochloric acid and dilute with water to about 25 ml. Carry out the extraction and aspiration as above. A special blank determination should be carried out so as to check the lead content of each batch of sulphuric acid, and magnesium nitrate, if used. STANDARD PROCEDURES598 ROSCHNIK: THE DETERMINATION OF LEAD IN FOODS BY [Analyst, Vol. 98 METHOD B (WET ASHING WITH SULPHURIC ACID AND HYDROGEN PEROXIDE)- Introduce 5 or l o g of homogenised food sample into a 400-ml tall-form beaker. Add about 5 ml of water to powders and other dry products.Add 10 ml of concentrated sulphuric acid, then 1 ml of 30 per cent. hydrogen peroxide. Allow any reaction to subside, then warm the beaker gently, avoiding frothing, and finally bring the contents to the boil. When the reaction subsides or if intense charring takes place add a few more drops of hydrogen peroxide. Continue until no vigorous reaction occurs on the addition of hydrogen peroxide (Note 1). NOTE 1- Products containing appreciable amounts of fat need to be treated for a longer time and heated more vigorously to drive off the more volatile fatty materials. Cool the beaker and contents, add 50 ml of water, and then transfer the solution quanti- tatively to a 100-ml calibrated flask by means of 6 N sulphuric acid contained in a wash-bottle.The final volume should be about 70 ml. Cool the solution, add 5 ml of xylene containing 1 per cent. of diethylammonium diethyldithiocarbamate, extract and continue as given under Method A. Calibrate in the same way as before, but use 70 ml of 6 N sulphuric acid instead of 5 ml of 6 N hydrochloric acid. METHOD C (RAPID PROCEDURE)- Introduce 2 or 5 g of material into a 50-ml calibrated flask and add 20 ml of 2 N hydro- chloric acid. Heat the mixture on a boiling water bath for 15 minutes or until dissolution is complete. Cool the solution and dilute it to about 30 ml with water. Add 5 ml of xylene containing 1 per cent. of diethylammonium diethyldithiocarbamate, extract and continue as described under Method A (but see Note 2 ) . Calibrate in the same way as before, but use 20 ml of 2 N hydrochloric acid instead of 5 ml of 6 N acid. METHOD D (PROCEDURE FOR FRUIT JUICES AND BEVERAGES)- Introduce 25 g of material into a 50-ml calibrated flask and add 5 ml of 6 N hydrochloric acid.Heat the mixture on a boiling water bath for 5 minutes. Cool the solution and add 5 ml of xylene containing 1 per cent. of diethylammonium diethyldithiocarbamate ; extract and continue as described under Method A (see Note 2). Degradation need not be complete and the final solution need not be colourless. NOTE 2- sufficient amount of the organic phase for aspiration. In methods C and D it is sometimes necessary to centrifuge the mixture briefly so as to obtain a OTHER METHODS- When required, determinations were carried out after wet ashing with sulphuric and nitric acids.In this instance the last traces of nitric acid and oxides of nitrogen had to be eliminated before dilution to give a solution that was 6 N in sulphuric acid. From this stage Method B was followed. Colorimetric lead determinations were carried out on the dissolved ashes by use of the diphenylt hiocarbazone (dithizone) method. 23 DISCUSSION AND RESULTS ORGANIC EXTRACTION SYSTEM- In order to test the effect of acidity on the extractability of lead, 5 ml of a 1 per cent. solution of diethylammonium diethyldithiocarbamate in xylene were added to a series of separating funnels containing 0, 10, 20, 30 and 40pg of lead in 30ml of the appropriate acid. The funnels were shaken for 1 minute, the organic phases were collected and then aspirated after 10 minutes.For comparative purposes the tests were repeated by using the ammonium tetramethylenedithiocarbamate - xylene and ammonium tetramethylene- dithiocarbamate - isobutyl methyl ketone systems. In these instances, 5 ml of the 1 per cent. solution of ammonium tetramethylenedithiocarbamate in water were added first, followed by 5 ml of the solvent. The actual acidity at the time of extraction was therefore lower than that indicated. The upper limits of acidity consistent with satisfactory sensitivity and a Linear calibration graph are given in Table I1 for the three systems.August, 19731 ATOMIC-ABSORPTION SPECTROPHOTOMETRY 599 TABLE I1 MAXIMUM ACIDITIES FOR THE SATISFACTORY EXTRACTION OF LEAD WHEN USING VARIOUS CHELATE - SOLVENT SYSTEMS ' With ammonium With ammonium With diethylammonium tetramethylene- tetramethylene- diethyldithiocarbamate - dithiocarbamate - dithiocarbamate - isobutyl Acid xylene/N xylene/N methyl ketone/N H30, 12 12 12 HC1 4 2 2 HNO, 4 2 0-5 The results for 12 N sulphuric acid (about 30 per cent.V/V) indicate that lead extraction can take place at high hydrogen-ion concentrations. With nitric acid, the reagents are presumably oxidised at high acidities. When hydrochloric acid is used, formation of PbCld2- begins to occur in preference to complexation with the organic reagent as the acidity is increased. This behaviour was confirmed for the diethylammonium diethyldithiocarbamate - xylene system by extracting 20 pg of lead from 30 ml of 2 N hydrochloric acid containing various amounts of sodium chloride and sodium sulphate.Recoveries were as follows : Salt Concentration/N Recovery, per cent. No salt added - 100 NaCl 2 37 NaCl 4 0 Na2SO4 2 100 NG304 4 100 With diethylammonium diethyldithiocarbamate - xylene, the extractability from 6 N sulphuric acid was unaffected when 1 ml of 30 per cent. hydrogen peroxide was added to the separating funnels. However, no lead was extracted when 1 ml of 65 per cent. nitric acid was added (k, no extraction took place from a mixture that was about 6 N in sulphuric acid and 0.5 N in nitric acid). At the other end of the pH scale, lead is extracted up to pH In practice, final acidities of 1 to 2 N for hydrochloric acid and of about 6 N for sulphuric acid were used after dry and wet ashing, respectively. At these acidities the sensitivity did not alter in response to slight changes in acidity, so that exact matching of the acidity of the standard and sample solutions is not required.The calibration graphs of the four methods described are linear up to at least 40 pg of lead. For all products studied the calibration graphs obtained by the method of additions are also linear and have the same slope as those given by the external standards. This similarity indicates that the extraction of lead into the organic phase is complete and that there are no matrix interferences in the organic phase. The results obtained with the two methods of calibration are the same. The effect on recovery of filling the calibrated flasks with water prior to aspiration was investigated. The recovery of 10 pg of lead in this way compared with that for extraction in a separating funnel (in which the organic phase does not come into further contact with water after phase separation) was 98 per cent.The loss is negligible in relation to the standard deviation of the methods. When the extract was shaken vigorously with 25 ml of water in a separating funnel, 98 per cent. of the lead remained in the organic phase, while 96 per cent. remained after two such extractions. It is considered that the addition of water down the side of the flask does not invalidate the results. Similar conclusions have been reached for lead with the ammonium t et rame t h ylenedit hiocarbamat e - isobu t yl methyl ketone system by other a ~ t h o r s . l ~ $ ~ ~ The diethylammonium diethyldithiocarbamate - lead chelate is relatively stable with respect to time.Recoveries of lead from the organic phase, left in contact with about 50 ml of aqueous solution in the calibrated flasks for various times at room temperature, were as follows : Time/hours Recovery, per cent. 0 100 2 98 24 70 72 0600 ROSCHNIK: THE DETERMINATION OF LEAD IN FOODS BY [Anabyd, VOl. 98 Provided that aspiration takes place within 2 hours of the extraction, results will be valid even if extraction of the standards and the sample solution are not performed simultaneously. The presence of iron and tin does not affect the extractability of .20 pg of lead by 5 ml of a 1 per cent. solution of diethylammonium diethyldithiocarbamate in xylene in amounts up to 10 mg of iron(I1) or iron(III), or 10 mg of tin(I1) or tin(1V).In the presence of 20 mg of iron(II1) no lead is extracted. As 5ml of 1 per cent. diethylammonium diethyldithio- carbamate solution corresponds to 50 mg of the solid it can be assumed that lead extraction is suppressed because all of the chelating agent has been used preferentially by the iron(II1). Such amounts of iron are not likely to be found in a food sample of 5 to 10 g (10 mg in 5 g corresponds to 2000 p.p.m.) and, in any event, the effect can be suppressed by the addition of ascorbic acid. The presence of 20 mg of tin(1V) did not affect the extractability of lead; with 20 mg of tin(II), however, only 77 per cent. of 20pg of lead was extracted. Again, such levels of tin are most unlikely to occur in a 5 to 10-g food sample.After ashing or acid digestion most of the tin would be in the form of tin(1V). The diethylammonium diethyldithiocarbamate - xylene extraction system used here possesses the following advantages over the more widely used ammonium tetramethylene- dithiocarbamate - isobutyl methyl ketone system. 1. Xylene is superior to isobutyl methyl ketone for reasons of solubility as virtually no xylene is dissolved in the aqueous phase (0.02 g per 100 ml of water). As a result of this lack of solubility the volume of the aqueous phase need not be kept rigidly constant throughout one series of determinations, nor is it necessary to saturate the xylene with water before use. 2. Diethylammonium diethyldithiocarbamate is soluble in xylene. The two can there- fore be added in one operation.However, ammonium tetramethylenedithiocarbamate must be added in aqueous solution separately from the organic solvent. Use of diethylammonium diethyldithiocarbamate allows the use of solutions that contain more hydrochloric and nitric acids. With ammonium tetramethylenedithiocarba- mate neutralisation or pH adjustment is usually carried out in p r a c t i ~ e . ~ J ~ - ~ ~ 4. Diethylammonium diethyldithiocarbamate is less sensitive to oxidising agents than is ammonium tetramethylenedithiocarbamate; it is more stable to nitric acid, for example. PRE-TREATMENT- Much has been written on the relative merits of dry and wet ashing for lead determina- t i ~ n ~ . ~ ~ y ~ ~ s ~ ~ We generally prefer dry ashing, because it normally requires less supervision and lends itself more readily to dealing with large numbers of samples, and because the risks of contamination are reduced.Some products, however, require sulphuric acid to be present in order to prevent volatilisation of lead, and a maximum temperature of 500 "C must not be exceeded in this instance. Calcination may therefore take a long time and certain products cannot be ashed satisfactorily without the addition of nitrates. The risk of the occurrence of losses by volatilisation is eliminated, but contamination from large amounts of reagents is more likely. As has been stated by several authors, samples high in calcium may give low results if sulphuric acid is used. In Method B, hydrogen peroxide is used rather than nitric acid for three main reasons. First, trace amounts of nitric acid must be removed before the addition of diethylammonium diethyldithiocarbamate if lead extraction is to be complete. Trace amounts of hydrogen peroxide do not affect the extractability of lead from 6 N sulphuric acid.Also with hydrogen peroxide, degradation need not be complete and the final solution can be dark in colour without invalidating the results. Therefore, the method involving the use of hydrogen peroxide requires much less time. Secondly, lead losses by co- precipitation with calcium sulphate occurred very much less often when hydrogen peroxide was used than when nitric acid was used in the presence of sulphuric acid. The mixture remains more dilute because with nitric acid the removal of the last traces of nitric acid by boiling results in dehydrating conditions that favour the precipitation of calcium sulphate.Thirdly, wet ashing with sulphuric and nitric acids gives results that are too low for products with tin contents above about 150 p.p.m., i.e., for certain canned foods. The effect is due to the nitric acid in combination with the tin, as it was not noticed when wet ashing was performed with sulphuric acid and hydrogen peroxide (Tables I11 and IV). Because tin does not affect the extractability of lead at these concentrations the phenomenon was un- doubtedly caused by the precipitation of hydrated tin oxides, which absorbed lead. 3. Wet ashing is the more rapid method for single samples.August, 19731 ATOMIC-ABSORPTION SPECTROPHOTOMETRY TABLE I11 RECOVERY OF 20 pg OF LEAD FROM REAGENT BLANK SOLUTIONS CONTAINING VARIOUS AMOUNTS OF TIN Recovery of lead, per cent., by wet-ashing with 601 Tin added/pg HiSO, - H202 H,SO, - H ~ O , G 100 100 500 100 95 1000 100 24 2500 100 0 A similar effect was observed after dry ashing.In the absence of tin, dissolution of the ashes in hydrochloric or nitric acid gave the same results for lead. In the presence of tin, however, the recovery of lead was incomplete when nitric acid was used. This observation is in accordance with the known solubilities of tin(1V) oxide in hydrochloric and nitric acids. TABLE IV LEAD FOUND IN A VARIETY OF FOODS AFTER VARIOUS METHODS OF ASHING Recovery, p.p.m., following dry ashing: solution in Recovery, p.p.m., following wet ashing with Tin, - r Food p.p.m.HC1 HNO, H,SO, - H20, H2SO& - HNO, Tomato purde . . . 520 6-92 2.52 7.16 0 Curry sauce . . .. 510 0.30 0.11 0.30 0 Puszta soup . . .. 82 0.22 0-22 0.21 0.22 RESULTS OF ANALYSES- The results obtained by atomic-absorption spectrophotometry after various methods of ashing are presented in Table IV. The results for a crude seasoning, obtained by use of Methods A and B, as well as with dry ashing followed by colorimetric lead determination, are listed in Table V. The seasoning comprised about 50 per cent. m/m of dry matter plus about 16 per cent. mlm of sodium chloride, and may be considered to be a"difficult"substance, with respect to both ashing and atomic-absorption spectrophotometry. TABLE V Five-gram sample used LEAD FOUND IN A CRUDE SEASONING BY VARIOUS METHODS Lead found by use of Method A: dry ashing, followed by atomic-absorption spectrophotometry, p.p.m. 1-38 0.94 1.14 1.18 1.27 1.15 1.21 1.20 1-17 Mean ... . 1.18 Standard deviation 0- 12 Degrees of freedom. . 8 Lead found by use of Method B: wet ashing, followed by atomic-absorption spectrophotometry, p.p.m. 1-14 1.18 1-16 - - Lead found by use of dry ashing, followed by colorimetry, p.p.m. 1.00 1-04 1-03 1.26 1.09 1.16 - 1.10 The results show good agreement and indicate that the atomic-absorption and colori- metric methods give comparable results and also that there is no loss of lead during ashing. The standard deviation for Method A is rather high for this product. Values found for three602 ROSCHNIK: THE DETERMINATION OF LEAD I N FOODS BY [APZalySt, VOl.98 more “normal” products, a goulash soup, a “Russian salad” (mixed vegetables) and a baby food (chicken dinner), are given in Table VI. TABLE VI LEAD FOUND IN VARIOUS FOODS BY USING METHODS A AND B Lead content, p.p.m. Method , . .. .. Gohash soup r------\ A B 0.1 8 0.22 0.18 0-16 0.16 - 0.18 - 0.18 - 0.17 - 0.14 - 0.14 - 0.20 - 0.21 I Mixed vegetables m 0.23 0.18 0.23 0.20 0-23 0.22 I 0.20 - 0.20 - 0.22 - 0.20 - 0.20 - 0-20 - 0.22 C h i c k e n n e r +- A B 0.07 0.11 0.10 0.1 1 0.08 - 0.17 - 0.08 - 0.14 - 0.1 1 - 0.13 - 0-1 1 - 0.08 - Mean . . .. .. . . 0.174 - - 0.204 0-107 - Standard deviation . . . . 0.023 - - 0.013 0.032 - - 9 9 I I Degrees of freedom . . . . 9 DETECTION LIMIT AND SENSITIVITY- The 283.3-nm wavelength line on the atomic-absorption instrument was chosen in preference to the 217-0-nm line because it is less noisy (the sensitivity when using the 217.0- nm line is about twice that for the 283.3-nm line, but it is difficult to translate this extra sensitivity into an improvement of the detection limit or of the precision because the 217.0-nm line is much noisier) and, more important, because the calibration is linear over a longer range.The detection limit in foods, found by using 10-g samples, is about 042 p.p.m. under the conditions of Methods A and B. A further improvement should be obtained with integrating facilities or a high-intensity lamp, or both. At present, this limit precludes the methods from giving exact values for uncontaminated milk,27-29 for which a 50-ml sample is required.RAPID PROCEDURES- The ashing step is not required for certain products that give a uniform suspension or a solution in water. Dissolution or suspension in 2 N hydrochloric acid, usually with heating, is satisfactory. In this instance the whole determination is carried out in a single calibrated flask and can be completed in 30 to 40 minutes (Method C). The results obtained by use of this method are given in Table VII for tomato and apple purkes. As all the lead in these products is extracted into the organic phase by diethyl- ammonium diethyldithiocarbamate, it is presumably present in the ionic form or else so loosely bound to the proteins that it is separated by acidification and warming. The recovery of added lead was found to be 100 per cent. for saccharose on a 5-g sample.The rapid method, however, fails for lactose, full and skimmed milk powders because too much emulsion is formed on shaking. These last products must be ashed. Liquid milk also creates too much emulsion and must be ashed. Recoveries of added lead were equally satisfactory for fruit juices and beverages, but normal levels of lead in these products, when uncontaminated, are too low to enable accurate results to be obtained.21~30--32 For these, Method D, which entails the use of a larger sample size (25 g), gives a slight improvement and is preferred. The recovery of lead remains at 100 per cent. and the detection limit is less than 0.01 p.p.m. Method D is equally applicable to carbonated beverages, although it may be necessary to decarbonate them before analysis so as to avoid excessive formation of froth and emulsion on shaking.It is also successful for beer; no wines or spirits were included in the study. No fruit juice or beverage was found that contained sufficient lead to facilitate the determination of a significant value for the standard deviation with Method D. The results for an artificially contaminated fruit juice are included in Table VII.August, 19731 ATOMIC-ABSORPTION SPECTROPHOTOMETRY 603 We have also used Method C to monitor the lead content of miscellaneous food additives, such as spice extracts, iron salts and lactic acid. With iron salts, such as the saccharate and other products containing more than about 0-2 per cent. of iron, ascorbic acid (5 ml of a 10 per cent. solution) is added to reduce the iron to its bivalent state..For lactic acid, the method of additions must be used for calibration because the partial solubility of lactic acid in xylene changes its viscosity, and thus its sensitivity (slope of the graph given by the sample relative to that given by the external standards). Some results for iron saccharate are given in Table VII. TABLE VII LEAD DETERMINATION IN VARIOUS MATERIALS BY THE RAPID METHODS Lead content, p.p.m. Appie purCe, Method C* (10-g sample) 0.13 0.15 0.13 0.16 0-13 0.13 0.14 0.15 0.15 - Mean . . .. .. 0.14 Standard deviation . . 0.012 Degrees of freedom . . 8 Tomato purde, Method C (5-g sample) 1.90 1-76 1-84 1.84 1-76 1.82 1.88 1.88 1-82 1.76 1-83 0.053 9 Orange juice, Method D* 0.67 0.65 0.62 0.60 0.60 0.62 0.62 0.62 0.60 0.60 0.62 0.024 9 Iron saccharate, Method C (2-g sample) 2.0 2.2 2.4 1.8 1.9 1.9 2.1 1.9 1.9 2.1 2-02 0.181 9 Lead content, p.p.m., by- Method B Method B 0.15 1.80 0.14 1.77 * With centrifugation.dry ashing,' followed by colorimetry 1-95 1.90 EXTRACTION OF OTHER ELEMENTS- According to the literat~re,~~9~3 several elements in addition to lead can be extracted into carbon tetrachloride or chloroform with diethylammonium diethyldithiocarbamate. Of these, silver, arsenic, bismuth, cadmium, copper, iron( III), mercury, molybdenum, selenium and zinc are probably of most interest in foods. Provided that a suitable method of pre-treatment is available, there seems to be no reason why the diethylammonium diethyldithiocarbamate - xylene extraction system should not give equally reliable results for more than one of these elements, determined in the final extract from a single sample.We have used it successfully for the simultaneous determination of lead and copper in lactic acid. It was also confirmed that after wet ashing of a goulash soup according to Method B, cadmium and lead could be determined together in the final extract and that the recovery of added cadmium was 100 per cent. The author acknowledges the assistance given by Mr. L. Obert in the experimental work. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. Truffert, L., Voeding, 1955, 16, 738. Szarski, P., F a Technol. Aust., 1971, 23, 216. 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