摘要:

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. Engst, R., and Woggon, H., Nahrung, 1965, 9, 889. Lehnert, G., Stadelmann, G., Schaller, K.-H., and Szadkowski, D., Arch. Hyg.Baht., 1969,153,403. Zook, E. G., Greene, F. E., and Morris, E. R., Cereal Chem., 1970, 47, 720. Warren, H. V., and Delavault, R. E., J . Sci. F d Agric., 1962, 13, 96. Meranger, j. C., and Somers, E., Bull. Envir. Contam. Toxicol., 1968, 3, 360. Klein, M., Namer, R., Harpur, E., and Corbin, R., New Engl. J . Med., 1970, 283, 669. Bergner, K. G., and Miethke, H., 2. Lebensmittelunters. u. -Forsch., 1964, 125, 406.604 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. ROSCHNIK Bergner, K. G., and Riidt, U., Ibid., 1968, 137, 337. Zuber, R., Mitt. Geb. Lebensmittelunters. u. Hyg., 1972, 63, 229. Abson, D., and Lipscomb, A. G., Analyst, 1957, 82, 152. Horwicz, W., Editor, “Official Methods of Analysis of the Association of Official Analytical Chemists,” Eleventh Edition, Association of Official Analytical Chemists, Washington, D.C. , 1970, Section 25.044. Dalton, A., and Malanoski, A., J . Ass. Off. Analyt. Chem., 1969, 52, 1035. Hoover, W. L., Reagor, J. C., and Garner, J. C., Ibid., 1969, 52, 708. Hoover, W. L., Ibid., 1972, 55, 737. Fletcher, K., J . Sci. Fd Agric., 1971, 22, 260. Yeager, D. W., Cholak, J., and Henderson, E. W., Envir. Sci. Technol., 1971, 5, 1020. Murthy, G. K., Rhea, U., and Peeler, J. T., J . Dairy Sci., 1967, 50, 651. Mack, D., and Berg, H., Dt. Lebensmitt-Rdsch., 1972, 68, 262. Gherardi, S., and Casoli, U., Industria Conserve, 1969, 44, 296. Jordan, J., Atom. Absorption Newsl., 1968, 7, 48. “Food Chemicals Codex,” National Academy of Science-National Research Council, Washington, Bode, H., and Neumann, F., 2. analyt. Chem., 1960, 172, 1. Chau, Y. K., Lum-Shue-Chan, K., Analytica Chim. Acta, 1969, 48, 434. Gajan, R. J., and Larry, D., J . Ass. Off. Analyt. Chem., 1972, 55, 727. Russel, H., Arch. Lebensmittelhyg., 1966, 16, 82. Brand, M., and Bentz, J . M., Microchem. J.. 1971, 16, 113. Stelte, W., 2. Lebensmittelunters. u. -Forsch., 1971, 146, 258. Roth, F., and Gilbert, E., Mitt. Rebe u. Wein, Obstbau u. Friichteverwert., 1969, 19, 430. Meranger, J. C., Bull. Envir. Contam. Toxicol., 1970, 5, 271. Meranger, J. C., and Somers, E., J . Ass. Off. Analyt. Chem., 1968, 51, 922. Forster, H., J. Radioanalyt. Chem., 1970, 4, 1. D.C., 1966, p. 278. Received December 6th, 1972 Accepted February 27th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800596

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, August, 1973, Vol. 98, $p. 605-609 605 A Critical Study of Safranine 0 as a Spectrophotometric Reagent: a Rapid Method for the Determination of Trace Amounts of Antimony in Steel BY C. BURGESS,* A. G. FOGG AND D. THORBURN BURNS (Department of Chemistry, University of Technology, Loughborough, Leicestershire, LE11 3T U) The behaviour of Safranine 0 (Basic red 2, C.I. 50240) in aqueous solutions has been investigated and its suitability as a spectrophotometric reagent is evaluated and discussed. A rapid method for the determination of antimony as a hexachloroantimonate (V) ion-association complex with Safranine 0 is described. This complex is extracted into benzene and is determined spectro- photometrically. The method is as sensitive and reproducible as the Rhod- amine B method but i t has the advantage that the determination can be carried out directly on solutions of steel without prior separation.Good agreement was found with standardised antimony values for five British Chemical Standards' steels. A REVIEW of the literat~rel-~ has shown that many workers have recently found basic dyes to be useful in determining large anions, and particularly P-block elements, as ion-association complexes. From the point of view of solution chemistry, however, the most important dis- advantage of basic dyes is their behaviour in aqueous acidic solutions, i.e., the slow protonation of the one or more basic amino groups present, and hence the lack of equilibrium in the aqueous phase during the extraction process. Xanthene dyes usually protonate very rapidly in aqueous solution but those in common use have two drawbacks: the ion pairs produced do not form true solutions, but can give rise to unstable colloidal suspensions4; and xanthene dyes can lactonise and be extracted in this colourless form.The extracted lactone can revert to the highly coloured quinonoid form under certain condition^.^^^ Various other dye groups have been investigated in these studies and 'Safranine 0 (Basic red 2, C.I. 50240), an azine dye, was found to show promise as a potential reagent for antimony. EXPERIMENTAL Safranine 0 protonates in acidic solution to yield the three forms shown in Fig. 1. The singly protonated blue form predominates in a solution of 5 to 7 M hydrochloric acid, but a t higher acidities its concentration decreases. The analytically useful R+ dye cation is virtually non-existent at a hydrochloric acid concentration higher than 6 RI.The above conclusions were reached after considering the spectra of 0.0035 per cent. m/V solutions of Safranine 0 in solutions of various concentrations of hydrochloric acid, obtained in 10-mm glass cells with water as the reference solution (Fig. 2). It was found that at hydrochloric acid concentrations of 5~ and above, the absorbance at 520nm was due almost entirely to the band overlap of the blue form (Amax. = 593 nm). Ideally, a dye cation that is not protonated in highly acidic solutions would be useful for the complexation of anions such as the hexachloroantimonate(V) ion, which are formed only under acidic conditions.This is true of Safranine 0 in 2 M hydrochloric acid, the optimum acidity for the formation and extraction of the complex formed with hexachloro- antimonate(V), for which the R+ form predominates. It was noted that the molar absorptivities of Safranine 0 complexes were solvent dependent, in direct contrast with Brilliant green systems previously studied.2$ In order to examine this effect, a pure Safranine 0 salt that was soluble in a range of solvents was required; the tetrachloroaurate(II1) salt was chosen because of its ease of preparation and its stability. Safranine 0 tetrachloroaurate(II1) was prepared by precipitating the dye from an acidic, alcoholic solution with sodium tetrachloroaurate(II1). The precipitate was filtered off, washed well with water and dried at 110 "C.Analysis of the salt, by ignition * Present address : Department of Chemistry, The University, Southampton, SO9 5NH. @ SAC and the authors.606 BURGESS et al. : SAFRANINE o AS A SPECTROPHOTOMETRIC [AnaZyst,bVol. 98 t tH+ Col ou rl ess Fig. 1. Equilibria of Safranine 0 in acidic solutions at 600°C to constant mass, showed the mean content of gold to be 29-3 per cent. (calcu- lated for C,,H,,N,AuCl,: 30-1 per cent.). A solution of this standard in 9 + 1 V/V dioxan - acetone, diluted with various other solvents, enabled molar absorptivities to be calculated. As dilution ratios of 100: 1 were used it was assumed that any original solvent effects would be swamped by the diluent. The results are shown in Fig. 3. The wavelength of maximum absorption varied from 522 to 538 nm.RH*+ form (593 nm) 0.00 0 2 4 6 8 1 0 1 2 Hydrochloric acid concentration/M Fig. 2. Variation of the forms of Safranine 0 with hydrochloric acid concentrationAugust, 19731 607 The reason for the variation of molar absorptivity with dielectric constant and the anomalous behaviour of alcohols is not clearly understood. It does explain, however, why some Russian workers needed to “stabilise” their extracts with ethanol or acetone when using non-triphenylmethane dyes.’ REAGENT IN THE DETERMINATION OF ANTIMONY IN STEEL 70 60 0 10 20 30 40 Dielectric constant Fig. 3. Molar absorptivity of Safranine 0 tetrachloro- aurate(II1) in various solvents : u, alcohols; 0 , solvents other than alcohols ; and 0, dioxan - water mixtures In a preliminary study of the suitability of Safranine 0 as a reagent for antimony, the extractability of the hexachloroantimonate(V) anion into various solvents was examined.By using values obtained from Fig. 3 it was possible to calculate the percentage recovery of the antimony, assuming that the molar absorptivities of the tetrachloroaurate( 111) and hexachloroantimonate(V) salts were identical in the same solvent. This assumption is reasonable as the chromophore in each instance is the dye cation. The results in Table I show that the higher apparent molar absorptivity obtained when isobutyl acetate rather than benzene is used as the extractant arises partly from the higher absolute molar absorptivity of the dye in isobutyl acetate and partly from a higher recovery of antimony.Subsequent work, however, showed that, of the solvents examined, only benzene could be used without interference from other ions present. The use of toluene in place of benzene was tried but, although free from interferences, it gave extracts that were not stable with time and much lower apparent molar absorptivities were obtained (see Table I). While this work was in progress, it was noted that Pilipenko and Shinhs had tentatively proposed a very similar method for the determination of antimony in steel. Their method, however, had not been applied to analysed steels and the extraction conditions were not optimised. TABLE I EXTRACTION RECOVERIES OF ANTIMONY UNDER EXPERIMENTAL CONDITIONS Apparent molar Calculated apparent absorptivity* / molar absorptivityt / Recovery, Solvent 1 mol-1 cm-1 x 1 mol-l cm-l x per cent.Benzene .. .. .. 27.0 34.4 78.5 Toluene .. .. .. 16.2 31.2 51.9 Isobutyl acetate . . .. 48-3 53.5 90.3 o-Dichlorobenzene . . . . 36.3 55.5 65.5 * Obtained from extraction studies. t Based on values shown in Fig. 3.608 BURGESS et al. : SAFRANINE o AS A SPECTROPHOTOMETRIC [Analyst, Vol. 98 As the purpose of this work was to develop a method for the determination of antimony in steel, the following procedure was adopted with benzene as the extractant, in spite of its inherent toxicity. CAUTION- Benzene is a carcinogen and a cumulative poison and care should be taken with its use. REAGENTS- Standard antimony solution, 1000 pg ml-l-An amount (1 -3343 g) of antimony potassium tartrate was dissolved in 50 per cent.V/V hydrochloric acid and the solution made up to 500 rnl in a calibrated flask. Working solutions containing 10 pg ml-l of antimony were made up by dilution of this standard with 50 per cent. V/V hydrochloric acid, and were prepared freshly when required. Pare iron sflonge- Johnson Matthey, Specpure grade. Sodium nitrite solution-A 10 per cent. m/V aqueous solution was prepared. Urea sohtion-A saturated aqueous solution was used. Potassium chloride solution-A 40 per cent. m/ V aqueous solution was prepared. Tin(I1) chloride solution-A 10 per cent. m/V solution was made up in 50 per cent. V/V Safranine 0 solution-A 0.1 per cent. m/V solution of the dyestuff in 0.1 M hydrochloric Hopkin and Williams RevectoR grade is suitable for use without further hydrochloric acid.acid was made up. purification. PROCEDURE- Dissolve 1.00 g of steel in 10 ml of a 9 + 1 V/V mixture of concentrated hydrochloric and nitric acids and boil the solution so as to remove oxides of nitrogen. Cool, and dilute to volume with concentrated hydrochloric acid in a 25-ml calibrated flask. Place 2-rnl volumes of this solution and 8-ml volumes of 50 per cent. V/V hydrochloric acid in 100-ml separating funnels and cool them in a refrigerator to less than 5 "C. Add tin(I1) chloride solution dropwise until all the yellow iron(II1) colour is discharged and then add P ml of sodium nitrite solution. Shake the funnels for 1 minute, then to each add 2 ml of saturated urea solution and 40 ml of potassium chloride solution, and shake for 14 to 2 minutes until all effervescence has ceased (carefully releasing the pressure from time to time).Add 5 ml of Safranine 0 solution to each mixture and extract twice with 10-ml portions of benzene. Filter the benzene extracts through a Whatman No. 31 filter-paper, combine the two extracts in a 25-ml calibrated flask and make up to volume with pure benzene, after washing the filter-paper well. Measure the absorbance of the well mixed extract in PO-mm glass cells at a wavelength of 527 nm. Prepare a calibration graph by using pure iron sponge and additions of standard antimony solution. RESULTS The calibration graph obtained was linear over the range 0 to 25 pg of antimony, with a small blank reading. The standard deviation a t the 20 pg of antimony level was less than 2 per cent.The results obtained when using British Chemical Standards' steels are given in Table 11. TABLE I1 DETERMINATION OF ANTIMONY IN BRITISH CHEMICAL STANDARDS' STEELS B.C.S. Antimony content, per cent. m/m Antimony found, Coefficient of variation, number (standard value) per cent. mlm* per cent. 325 0.002 0.0014 2.8 326 0.005 0.0055 4.0 327 0-033 0.034 ( 1 328 0.026 0.028 3.1 330 0.018 0.019 2.5 * Mean of six determinations.August, 19731 REAGENT IN THE DETERMINATION OF ANTIMONY IN STEEL 609 DISCUSSION The results obtained with the British Chemical Standards’ steel samples agree well, in most instances, with the standard values. The certificates of analysis of the standard steels indicated that the Rhodamine B method was used in obtaining the antimony value.The method generally adopted was that proposed by Kidman and Waite.9 In addition to the general disadvantages of xanthene dyes discussed earlier, the quanti- tative oxidation of antimony to antimony(V) was assumed to occur in the presence of nitric acid. Morellolo has since shown that the oxidation with nitric acid may be incomplete. In the recommended procedure, all of the antimony is reduced to the tervalent state prior to oxidation with sodium nitrite. The proposed method eliminates the necessity for evaporation to fumes and prior separation of the antimony required with the Rhodamine B method. Although the extraction of antimony is not complete, the extractability remains constant over the range studied. The procedure is rapid, the time for a single determination being largely dependent on the rate of dissolution of the steel sample.If dissolution is rapid, then the time taken for a complete determination is less than half an hour. Recently, Rhodamine S has been proposed as a reagent for antimony,ll but we experienced difficulties with this method owing to the large, variable blank values obtained. The authors thank Mr. J. A. Clark of Baird & Tatlock (Hopkin and Williams Division) for the gift of dyes and for much helpful discussion. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES Fogg, A. G., Burgess, C., and Thorburn Burns, D., Talanta, 1971, 18, 1175. Sandell, E. B., “Colorimetric Determination of Trace Metals,” Third Edition, Interscience Ramette, R. W., and Sandell, E. B., Analytica Chim. Acta, 1955, 13, 455. -- , J . Amer. Chem. SOG., 1956, 78, 4872. Blyum, I. A., and Pavlova, N. N., Zav. Lab., 1963, 29, 1407. Pilipenko, A. T., and Shinh, N. M., UKr. Khirn. Zh., 1966, 32, 1211; Analyt. Abstr., 1968, 15, 750. Kidman, L., and Waite, C. B., Metallurgia, 1962, 66, 143. Morello, B., Metallurgia Ital., 1966, 58, 317. Jablonski, W. Z., and Watson, C. A., Analyst, 1970, 95, 131. , 3 , Analyst, 1970, 95, 1012. --- , , Ibid., 1971, 96, 854. --- Publishers, New York, 1959, p. 258. Received November 30th, 1972 Accepted March lst, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800605

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

610 Analyst, August, 1973, Vol. 98, PP. 610-615 An Emanation Method for Determining Radium Using Liquid Scintillation Counting BY K. G. DARRALL, P. J. RICHARDSON AND J. F. C. TYLER (Defiartment of Trade and Industry, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ) A very simple emanation method for determining radium is described. Radon is adsorbed on silica gel at the temperature of liquid nitrogen and the silica gel is transferred a t 0 "C to a toluene-based liquid scintillator for counting in an automatic liquid scintillation spectrometer. The lowest limit of detection is 0.1 pCi of radon. MOST of the methods that have been developed for the determination of radium by the emanation method involve the use of complex de-emanation systems and a special detector, the scintillation chamber.Lucasl achieved an efficiency of detection of 5.4 counts min-l pCi-l of radon at a background level of 0.06 counts min-1 and this probably represents the peak of development. In the emanation method of the "Standard Methods for the Examination of Water and Wastewater"2 a Lucas cell is used. Other less complex systems have lower efficiency (E) and higher background (B) values; for example, E is 3.6 counts min-l pCi-l and B 1 count min-l according to Conlan, Henderson and Walton,3 and E is 2-5 counts min-l pCi-l and B 0.33 count min-1 according to Collinson and Hague.* Our need was for a simple system for occasional use for the determination of radium in effluents and waters, and for unsupported radon in waters, i.e., radon in excess of the equili- brium amount of radium parent, with a lower limit of detection of less than 1 pCi.It would be advantageous to use readily available counting equipment, and the automatic liquid scintillation spectrometer was attractive because of its high reliability and automatic facility for sample changing. It was expected that the high efficiency of alpha counting by liquid scintillation (100 per cent.) might offset the disadvantage of high background. Noguchi5 had attempted to use liquid scintillation counting for the determination of radon. After trapping the radon at the temperature of liquid nitrogen, without an adsorbent, he evaporated and collected it in a liquid scintillator but the results were not quantitative. Bonev and Akrabova6 also attempted to determine radium by direct dissolution of radon in a liquid scintillator. In the present investigation we have developed a system in which the main stages of ingrowth, de-emanation, trapping and counting can be carried out easily and simply with readily available apparatus.The radon is trapped on silica gel at the temperature of liquid nitrogen and transferred at 0 "C into the liquid scintillator, in which it is desorbed and counted. The losses of radon are small and reproducible. METHOD REAGENTS- Nitric acid, sp. gr. 1 -42-Analytical-reagent grade. Potassium hydroxide pellets-Analytical-reagent grade. Silica gel--"Purified" grade. Grind to a mesh size of 14 to 30 per inch and dry at 105 "C Liquid nitrogen. Toluene-based liquid scintillator, NE 233, or equivalent. Alkaline EDTA solution-Dissolve 10 g of the disodium salt of ethylenediaminetetra- for 2 days.acetic acidj5l.u~ l o g of sodium carbonate in water and dilute to 1 litre. APPARATUS- flasks of various sizes. temperature of the counting compartment was adjusted to 6 "C. The apparatus as shown in Fig. 1, with a selection of de-emanation heads (B) to fit Liquid scintillation spectrometer-We used a Packard, Model 3320 , Tri-carb and the @ SAC; Crown Copyright Reserved.DARRALL, RICHARDSON AND TYLER 61 1 PROCEDURE- Add sufficient nitric acid to the de- emanation flask (A) to make the acidity 0.3 N when the flask is full. Fill the flask with a measured volume of sample, fit the de-emanation head (B) and bubble nitrogen through the solution until a volume equal to ten times that of the sample has been passed.Stopper the flask, making sure that no air bubbles are present. If necessary top up the contents of the flask with distilled water. The de-emanation apparatus is shown in Fig. 1. Nitrogen R Rotameter I-38mrnd Fig. 1. Apparatus for de-emanation and trapping of radon (lettered parts are described in the text) Allow the solution to stand for the requisite ingrowth period and then remove the stopper and, without delay, connect the flask to B, which is already connected to the apparatus shown in Fig. 1. (During ingrowth the flask A is stoppered and is completely filled with solution. When the stopper is removed and replaced with B, there is a small displacement of solution equal to the volume of the glass frit and tube and then a large displacement is produced by bubbles when the nitrogen is turned on.) Pass ten volumes of nitrogen through the solution.Stop the flow, remove the flask containing liquid nitrogen and replace it with an ice-bath for 5 minutes. Remove the ice-bath, wipe the silica gel tube dry, disconnect it and pour the silica gel into 17 ml of liquid scintillator contained in a counting vial. Cap the vial, set it aside at room temperature for 3 hours, and then count. Carry out a blank and standard at the same time. From the standard derive E, the number of counts per minute per picocurie of radon. Then C Radium activity = - pCi where c is the number of counts per minute (less background) for the sample andf the ingrowth factor = 1 - e--At where t is the ingrowth period and h the disintegration constant for radon.Ef612 INGROWTH- The vessel used for ingrowth and de-emanation can be of any-size or shape but there may be restrictions on the material of construction. In this investigation only glass vessels with glass stoppers have been used. The vessel opening must, of course, be compatible with the de-emanation head. If a head-space remains, then radon will be lost when the stopper is removed. The solubility coefficient for radon in water is 0.25 at 20 "C, so the ratio of the concentration of radon in the gaseous phase to that in the aqueous phase is 4: 1. Thus, for a 1-litre flask with a 2-ml head-space, 0.8 per cent. of the radon is in the head-space, whereas with a 150-ml flask, the smallest used here, 5 per cent.of the radon is in the 2-ml head-space. The ingrowth period should be at least 4 days (50 per cent, ingrowth) and there is little advantage in extending it beyond 84 per cent. ingrowth at 10 days. DE-EMANATION- The de-emanation head is sufficiently long to provide space for bubbling and can be made bulbous if necessary. The end of the inner tube is fitted with a sintered-glass diffuser, which should reach nearly to the bottom of the de-emanation vessel; this arrangement is essential for efficient de-emanation.7 The sinter can become contaminated with radium, and the radon from this radium can appear in the first sample of a batch that is de-emanated. The sinter should therefore be stored in alkaline EDTA solution. Jacobi7 recommended a total flow of nitrogen of volume equal to ten times that of the sample and it appears from the present results [Fig.a(@)] that this is a satisfactory rule. DARRALL, RICHARDSON AND TYLER: AN EMANATION METHOD FOR [Aizalyst, Vol. 98 DISCUSSION During the ingrowth period the vessel must be full. c I 0 Q .- F I c .- E fn + C 3 0 I I t L 0 10 20 1 2 3 0 10 20 0 20 40 5 n n (el 0 20 4 Flow time/rninutes Mass of silica gel/g Warm-up time/ Warm-up temperature/OC Desorption Fig. 2. minutes ternperature/OC The effect on the efficiency (counts min--' pCi-1) of varying one a t a time the parameters (a) flow time, (b) mass of silica gel, (G) warm-up time, (d) warm-up temperature and (e) desorption temperature. The constant parameters were: flow time, 10 minutes; mass of silica gel, 3 g ; warm-up time, 5 minutes; warm-up temperature, 0 "C; flask volume: 0, 150 ml and x, 1 litre; flow-rate of nitrogen, 0.6 1 min-l. The gain and discriminator controls of the liquid scintillation spectrometer were set to detect the maximum number of particles DRYING- The nitrogen stream from the de-emanation vessel is dried over pellets of potassium hydroxide in the U-tube (C), which is re-charged for each de-emanation with 20g of the pellets. ADSORPTION ON SILICA GEL- The particle size of the silica gel is small enough to permit 100 per cent.adsorption of radon but large enough to give a stable bed at high nitrogen flow-rates and to have suitable pouring characteristics. The tube is charged with 3 g of silica gel and the diameter of the tube is such that the level of the bed is several centimetres above the top of the flask containing liquid nitrogen so as to minimise the condensation of radon on the walls of the tube.The variation in response with the mass of silica gel is shown in Fig. 2(b). The tube must not dipAugust, 19731 DETERMINING RADIUM USING LIQUID SCINTILLATION COUNTING 613 into the liquid nitrogen, but only into the vapour above it, otherwise nitrogen will condense in the tube and when the temperature is subsequently raised the boiling nitrogen will remove some of the radon from the silica gel. Even so, some nitrogen is adsorbed Qn the silica gel and for this reason the temperature is raised to 0 "C before adding the silica gel to the scintillator in order to prevent the release of this gas in the liquid scintillator.TRANSFER OF RADON TO SCINTILLATOR- When de-emanation is complete the nitrogen flow is stopped, the flask containing liquid nitrogen is replaced with an ice-bath and the tube warmed for 5 minutes. It is wiped dry, unclipped, the silica gel is poured through a funnel into a 20-ml counting vial containing 17 ml of scintillator, and the cap is replaced immediately. The volume of liquid scintillator is that which will give a small head-space, although the need for this precaution is not so great as with aqueous solutions, the solubility coefficient in toluene being 13.2 at 18 "C. The effects of warm-up time and temperature on the count-rate are shown in Fig. 2 (c) and (d). COUNTING- The decay scheme for radon-222, with half-lives and particles emitted as indicated, is as follows- 222Rn (3.825 days) I 2'8 Po (3.05 minutes) 214Bi 4 (19.7 minutes) I.*14Pb 6 (26.8 minutes) Radioactive equilibrium is reached after about 3 hours and the vials are left for this period before counting. The growth of activity as radioactive equilibrium is attained and the subsequent decay as measured on the liquid scintillation spectrometer are shown in Fig. 3. During the 3-hour period the radon and its daughters equilibrate between the silica gel and the scintillator. Most of the activity has been found to be present in the liquid scintillator and only a small proportion of the daughters remains adsorbed on the silica gel. Horrocks 0 1 2 3 4 , 5 Time from'de-emanation/days Fig. 3. scintillator Growth and decay of radon and its daughters in a liquid014 [Analyst, Vol.98 and Studiefl showed that there was some adsorption of the daughters on small glass vials of 0.025-ml volume. The final count-rate is independent of the temperature during the desorption period [Fig. 2 ( e ) ] . If the three alpha-particles and the two beta-particles were counted with 100 per cent. efficiency, 10.9 counts min-l pCi-l would be the maximum attainable over-all efficiency. In fact, only the alpha-particles are counted with an efficiency approaching 100 per cent., so that, in practice, when the gain and discriminator controls of the liquid scintillation spectrometer are set to detect the maximum number of particles, the highest efficiency observed is 7.0 counts min-l pCi-l of radon. Under these conditions the background is high at 60 counts min-l.The best conditions for counting, i e . , when the function (efficiency)2/(background) is at a maximum, are with the discriminators set as shown in the liquid scintillation spectrum recorded after the 3-hour equilibrium period in Fig. 4. At these optimum discriminator settings the over-all efficiency is 3.7 counts min-l pCi-l of radon and the background 6 counts min-l. The lower limit of detection at the 95 per cent. confidence level for a 100-minute count is then 0-1 pCi of radon, which, for example, is equivalent to 0.2 pCi of radium after 50 per cent. ingrowth. Normally, five samples and a blank are run and these are counted for 20-minute periods in five cycles, which takes 10 hours. There is about 7 per cent.decay during this time, but it need not be taken into account if the standard is counted in the same cycle pattern. DARRALL, RICHARDSON AND TYLER: AN EMANATION METHOD FOR 2400 1 I I 7 2000 - C .- E 3 1600 - C 3 " 1200 - 800 - 400 I 0 0 A B Disc rim inator setting Fig. 4. The liquid scintillation spectrum of radon and its daughters at equilibrium. A to B is the counting region, i.e., A is the lower discriminator setting and B is the upper discriminator setting TOTAL RADON- For total radon, the sample is taken directly in the de-emanation flask and care is taken to ensure that it is not aerated and that no head-space remains. The radon obtained from the first de-emanation is the total radon, and that from the second de-emanation, after a period of ingrowth, is the radon in equilibrium with radium. Some natural waters have a total radon activity several thousand times greater than the radium activity, e.g., 20 000 pCi 1-1 of radon and 10 pCi 1-1 of radium.In this event, it is necessary to ensure that the remnants of the unsupported radon have been removed by additional periods of de-emanation before the start of the ingrowth period. RESULTS The recovery of radon was measured in two series of experiments by adding variousAugust, 19731 DETERMINING RADIUM USING LIQUID SCINTILLATION COUNTING 615 amounts of a radium standard obtained from The Radiochemical Centre to de-ionised water contained in the de-emanation flask (see Table I). TABLE I RECOVERY OF RADIUM-226 FROM 1 LITRE OF WATER Radium added/pCi Radium found/pCi 0.95 1.04 f 0.33 1.90 1.71 f 0.34 4.73 4.52 f 0.38 9.47 9-75 f 0.45 18-93 19.29 & 0.55 47.34 47-13 f 0.77 11 8.2 117.7 f 1-2 0.65 f 0.28 1.88 f 0.30 3-19 & 0.32 3.69 f 0.33 5.08 f.0.35 5-05 f 0.35 1 ::;: 2-85 \ 34:;: 5.70 1 Series I Ingrowth factor 0.498 Series I1 Ingrowth factor 0.585 The radium in a series of effluents was determined by the emanation method and by The limits of detection and the statistical limits shown in Tables I and 11 are based on a barium sulphate co-precipitation method9 (see Table 11). counting only and are for 1-64 times the standard deviation. TABLE I1 RESULTS FOR THE DETERMINATION OF RADIUM-226 I N EFFLUENTS Radium-226, pCi l-l, by Total activity, pCi 1-1 f A A \ I \ Effluent Present method Chemical method Alpha-activity Beta-activity 60.1 & 0-9 99.4 f 1.1 <0*14 <0.14 (0.14 23-9 f 0.8 78.5 f 1.2 41-0 & 0.9 203.3 f 2-0 64-1 106.0 0.10 f 0.02 0.21 & 0.02 0.36 f 0.02 25-2 64.9 48.9 210.0 310 440 80 70 170 433 320 460 1000 18 000 14 000 88 000 44 000 47 000 7000 32 000 34 000 108 000 It is difficult to assess the accuracy of the chemical method, for radium-224 was present in the effluents in amounts up to one third of the radium-226 activity. Therefore, the total radium activity had to be resolved into its component activities by following the change in activity over a period of a few weeks,1° except that with effluents C, D and E, in which the radium activity was very low, any radium-224 activity was allowed to decay away for 1 month before the source was counted.It is doubtful whether the activity recorded by the chemical method for effluents C, D and E was from radium for it was about one five- hundredth of the total alpha-activity of the effluent, and in a barium co-precipitation method the decontamination might not be more efficient than is indicated by this result. We thank the Government Chemist for permission to publish this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Lucas, H. F., in Adams, J. A. S., and Lowder, W. M., Editors, “The Natural Radiation Environ- “Standard Methods for the Examination of Water and Wastewater,’’ Thirteenth Edition, A.P.H.A., Conlan, B., Henderson, P., and Walton, A., Analyst, 1969, 94, 15. Collinson, A. J. L., and Hague, A. K. M. M., J . Scient. Instrum., 1963, 40, 521, Noguchi, M., Radio-Isotopes, 1964, 13, 362. Bonev, L., and Akrabova, A., Resztgenol. Radiol., 1966, 5, 259. Jacobi, R. B., J . Chem. Soc., 1949, S314. Horrocks, D. L., and Studier, M. H., Analyt. Chem., 1964, 36, 2077. Rosholt, J. N., jun., Ibid., 1957, 29, 1398. Coomber, D. I., Proc. SOG. Wat. Treat. Exam., 1963, 12, 106. ment,” University of Chicago, Chicago, 1964, p. 327. A.W.W.A. and W.P.C.F., New York, 1971, p. 617. Received December 20th, 1972 Accepted Mwch 7th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800610

出版商:RSC    

年代:1973

数据来源: RSC

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616 Analyst, August, 1973, Vol. 98, pp. 616-623 Analytical Methods Committee REPORT PREPARED BY THE ESSENTIAL OILS SUB-COMMITTEE Application of Gas - Liquid Chromatography to the Analysis of Essential Oils Part 11.” Determination of 1,8-Cineole in Oils of Cardamom, Rosemary, Sage and Spike Lavender THE Analytical Methods Committee has received the following report from its Essential Oils Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The constitution of the Essential Oils Sub-committee responsible for the preparation of this report was: Mr. A. M. Humphrey (Chairman), Mr. J. H. Greaves, Mr. B. E. Kent, Mr. W. S. Matthews, Mr. R. G. Perry, Mr. J. Ridlington, Mr. R. A. Stocks and Mr.G. Watson, with Mr. P. W. Shallis as Secretary. INTRODUCTION The oxide l,S-cineole, C,,H,,O, is a constituent of many essential oils, including carda- mom, eucalyptus, lavender, rosemary, sage and spike lavender. The determination of cineole in essential oils has interested analysts for many years and several different methods have been proposed, none of which is entirely satisfactory. The application of gas chromatography to the determination of cineole was therefore studied by the Essential Oils Sub-committee of the Analytical Methods Committee of the Society for Analytical Chemistry. HISTORICAL REVIEW Among the early analytical methods were those based on freezing-point determina- tions,lP2 but such methods were generally restricted to oils of high cineole content. Cocking3 recommended the formation of a cineole - o-cresol complex from which the original concen- tration of cineole could be assessed, but it has been shown to be unsatisfactory for certain oils of eucalyptus that contain only small amounts of cineole, and Cross, Gunn and Stevens4 demonstrated the shortcomings of the method by means of infrared spectrophotometry when applied to a range of oils of spike lavender.Other methods involving complex formation were based on the use of l-naphth~l,~ resorcino16 and phosphoric acid,’ but such techniques necessitated a high initial level of cineole in the oils. A spectrophotometric method of utilising the development of a colour with an acidic solution of 9-dimethylaminobenzaldehyde8 was proposed, but has subsequently been criticised by Montes.g Infrared spectra of many essential oils containing cineole have been presented by Naves,lo Presnellll and Maennchen,12 but the work described by Cross, Gunn and Stevens4 appears to be the first quantitative approach to the determination of cineole by this technique.The Essential Oils Sub-committee, in its report issued in 1931,13 included a detailed study of the o-cresol method of analysis, which has been included in the Society’s book of standardised and recommended methods14 and as a B.S.I. recommendation.15 The Sub-committee responsible for the work a t that time made the following statement : “The presence of alcohols, esters, aldehydes and ketones in quantity in cineole-containing oils has been shown to raise the freezing-point of the o-cresol compound, The method, therefore, indicates a higher result than the actual content.No means has been found for carrying out accurate determinations under these conditions, but the Sub-committee is of the opinion that the ‘apparent’ cineole content shown by the o-cresol method has a consider- able value. Fractions of eucalyptus oil are frequently used as adulterants in rosemary oil, and the apparent cineole content is a useful figure in the examination of such oils. The Sub-committee recommends that the term ‘Apparent Cineole Content by o-Cresol’ should be used in connection with the oils of rosemary, spike and sage.” * For particulars of Part I of this series, see reference list, p. 623. @ SAC.ANALYTICAL METHODS COMMITTEE 617 EXPERIMENTAL The preliminary studies by gas chromatography of the determination of cineole included experiments on the resolution and recovery of mixtures of cineole, limonene, camphor and linalol.This work indicated that the flame-ionisation detector was particularly suitable for use in quantitative determinations, together with poly(ethy1ene glycol) (PEG) 400 as a stationary phase, but there could be problems with the satisfactory resolution of cineole. The collaborating laboratories then applied their usual gas-chromatographic procedures to the determination of cineole in a selection of essential oils of commercial quality, Three oils were investigated and the cineole contents reported ranged from 12.7 to 15-3 per cent. for oil of rosemary, from 27.2 to 32.5 per cent.for oil of spike lavender and from 3.2 to 7.7 per cent. for oil of lavender, 40/42. It was agreed that there was some difficulty in obtaining satisfactory resolution of the cineole peak in the oil of lavender. Accordingly, a further study was made of (i) a natural oil of French lavender, (ii) a natural oil of spike lavender, and two additional samples, prepared by adding a known amount of cineole (5 per cent.) to each of these oils. It was decided that certain operating conditions and the method of measurement should be specified in order to achieve some degree of standardisation. The following conditions were agreed for the tests : stationary phase, PEG 400; column tempera- ture, 75 to 85 “C; a flow-rate to ensure adequate resolution; flame-ionisation detector; and cyclohexyl acetate as the internal standard.The results and the method for the calculation of the peak areas are shown in Table I. TABLE I DETERMINATION OF CINEOLE (PER CENT. m/m) IN OILS OF FRENCH AND SPIKE LAVENDER AND THE OILS WITH ADDED CPNEOLE French French lavender Spike lavender Measure- ment* Laboratory lavender + cineole Spike lavender + cineole A 2-31, 2.03 6-1, 5.8, 5.7 24.2, 25.8, 27.5 32.1, 35.3, 31-8 (4 2.13, 2.04 B 3.6, 3-2, 3-3 6.5, 6.1 26.9, 28-4, 25.0 2.2, 2.2, 2-2 5.6, 5.7, 5.4 28-6, 29-1, 29.3 C 2-84, 2.88, 2.93 6.3, 6.4, 6.2 29.4, 29.8, 29.4 D 2.69, 2.67, 2.72 5.6, 5.7, 5.7 25.6, 27.0, 25.9, 27-0 2.92, 2.96, 2.90 5.7, 6.0, 5-8 26.2, 26.8, 25.5, 26.5 2-75, 2.65, 2.72 5.8, 5.7, 5.6 28.2, 27.8, 27.9, 28.4 E 1.97, 1.90, 1.93 5.0, 5.2, 5.1 27-4, 28.5, 27.4 F 1.76, 1.60 5.2, 5.3 24.0, 24.8 1.54, 1.46 4.6, 4.6 23.3, 24.6 1.53, 1.46 4.6, 4-6 23.1, 24.3 “Method of calculating peak “area”- 31.4, 33.6, 32.2 33.5, 34.5, 36.0 33.0, 33.3, 33-2 30.8, 30.5, 29-9, 29-3 27.6, 29-7, 29-1, 28.7 31.4, 31.8, 31.9, 31.8 32.7, 33.6, 32.9 30-3, 28.5 27-0, 27-3 26.6, 27-3 (a) Integration.( b ) (c) (d) Peak height only. Peak height x width a t half-height. Peak height x retention distance. The results indicated that with the oil of spike lavender, it is possible to recover the cineole with an accuracy of 100 & 10 per cent. Under similar operating conditions, the laboratories were unable to obtain adequate resolution of the cineole peak in oils of lavender so as to enable a satisfactory quantitative measurement to be made.The Sub-committee agreed that further studies would be necessary in order to develop a gas-chromatographic method for use with oils of low cineole content that would be acceptable to the analysts. It was further agreed that the o-cresol method was satisfactory for deter- mining cineole contents of oils of over 40 per cent. In view of the findings from the experi- ments on oil of spike lavender, it was decided to concentrate on a procedure that could be applied to the examination of essential oils with cineole contents in the range 10 to 40 per cent. For this investigation, a collaborative exercise was arranged on samples of oils of carda- mom, rosemary, sage and spike lavender. It was decided that certain operating conditions should be similar for all laboratories, as follows: the column packing was to be supplied618 ANALYTICAL METHODS COMMITTEE : APPLICATION OF GAS - LIQUID [Ana&St, VOl.98 from one source and to consist of 10 per cent. PEG 400 as stationary phase on Chromosorb W of 85 to 100 mesh, acid washed and silanised; cyclohexyl acetate as internal standard; column temperature 75 to 85 “C; and a flame-ionisation detector. The assessment of peak areas was carried out by the peak height x retention distance method and the mean was determined from triplicate results. This procedure was discussed by the Sub-Committee in a previous report.16 The results of these tests are shown in Table 11, from which it can be seen that good agreement between laboratories was obtained; typical tracings for the different oils are shown in Figs.1 to 5. TABLE I1 DETERMINATION OF CINEOLE IN OILS OF CARDAMOM, ROSEMARY, SAGE AND SPIKE LAVENDER Cineole found, per cent. rnim Oil Sage .. .. * . Spike lavender . . Cardamom .. .. Laboratory 1 A B C D F G H A B C D F G H A B C D F G H J J J Rosemary .. .. A B C D F G H J 11.91 11.98 12-19 10-80 10-8 11.67 11-73 25-19 25.13 25.40 24-60 25.5 25.22 24-61 29-10 28.88 29.37 28.85 27.1 28-80 29.05 42.91 41.74 40.87 40.95 42.0 40.68 42.03 - - - - 2 11.43 12.10 12.02 11-00 10.7 11.83 11-29 25.65 25.54 25.08 24.90 25.8 25.04 24-47 29.48 29-72 29.02 28-40 27.8 29.08 29-92 42-35 41-80 40-50 41-10 42.2 41.06 41.91 - - - - 3 12.03 11.98 11.20 10.8 11.95 11.86 26.09 25.02 24-70 24.8 24-99 24.86 30-07 29-01 28-50 27.4 28.99 29.29 - - - - - I 42.05 40.80 41-35 42-5 40.91 41.51 - Mean 11-7 12.0 12-1 11.0 10.8 11-8 11.7 11-6 25-4 25.3 25.2 24.7 28.4 25.1 24.4 24.6 29-3 29.6 29.1 28.6 27-4 29.0 28.8 29.4 42.6 41.9 40.7 41.1 42.2 40-9 41.1 41.8 The Sub-Committee considered that the high cineole content of the oil of rosemary shown in Table I1 indicated that it was not a typical sample.Further tests under similar operating conditions were carried out on authentic samples of oils of Spanish and Tunisian rosemary, and the results are shown in Table 111. VARIATION IN LABORATORY WORKING CONDITIONS- The operating conditions used by the collaborating laboratories are outlined in Table IV, PEG 400 was selected by the laboratories for use as the stationary phase as it was found to give satisfactory resolution and reproducible results.No apparent difference was observed in the results obtained by the use of either glass or stainless-steel columns. No difficulty was experienced by collaborating laboratories when using “on column” injection, but it was felt that unduly high “flash injection” temperatures, as used by some members, could have adverse effects on the stationary phase. It was determined by experi- ment that a minimum flash temperature of 110 “C was required in order to vaporise the sample without affecting the peak shapes and their resolutions. An injection temperature of 120 “CAugust, 19731 CHROMATOGRAPHY TO THE ANALYSIS OF ESSENTIAL OILS. PART I1 619 was considered preferable and a further experiment showed that this temperature did not make any noticeable difference to the performance of the column when operated under this condition for several days.TABLE I11 DETERMINATION OF CINEOLE IN OILS OF ROSEMARY Oil Spanish . . Tunisian . . Laboratory .. B D F €I J .. B D F H J 7 1 23.4 22.3 23.0 23-4 23.1 26.8 25.6 27.0 26.8 26.8 Cineole found, per cent. m/m A > 2 3 Mean 22-9 23.3 23-2 22.2 22.7 22.4 22.9 23.1 23.0 22.9 23.0 23.1 23.3 23-2 23.2 26.7 26.6 26.7 25.7 25.5 25.6 27.3 27.4 27.2 27.3 26.7 26.9 26-5 26-9 26.7 CONCLUSIONS Gas chromatography can be used for the quantitative determination of cineole. The results obtained from the series of oils of cardamom, rosemary, sage and spike lavender, containing cineole in the range of about 10 to 40 per cent., have enabled the Sub-committee to recommend the procedure described in the Appendix, which should give results of acceptable precision, both within and between laboratories.The recommended method affords a means of determining the cineole contents of the stated oils without interference from other com- ponents, which gives a determination of hitherto unattainable accuracy. Fig. 1. Typical chromatogram of oil of spike lavender, with cyclohexyl acetate as internal standard. Analysis time 18 hours620 ANALYTICAL METHODS COMMITTEE: APPLICATION OF GAS - LIQUID [AnaJySt, VOl. 98 Cyclohexyl acetate I 1 I \ Fig. 2. Typical chromatogram of oil of sage, with cyclo- hexyl acetate as internal standard. Analysis time 1 hour Cineole Fig. 3. Typical chromatogram of oil of cardamom, with cyclohexyl acetate as internal standard. Analysis time 2 hoursAugust, 19731 CHROMATOGRAPHY TO THE ANALYSIS OF ESSENTIAL OILS.PART 11 621 Cineole I Fig. 4. Typical chromatogram of oil of Tunisian rosemary, Analysis time with cyclohexyl acetate as internal standard. 1 hour Cineole Cyclohexyl acetate I I r I Fig. 5. Typical chromatogram of oil of Spanish rosemary, Analysis time with cyclohexyl acetate as internal standard. 1 hour622 ANALYTICAL METHODS COMMITTEE : A4PPLICATION OF GAS - LIQUID [AnQZJISt, VOl. 98 TABLE IV GAS-CHROMATOGRAPHIC OPERATING CONDITIONS USED BY THE DIFFERENT LABORATORIES A B C D F G H Instrument Pye 104 F & M 700 P.-E. F11 Pye 104 Pye 104 P.-E. 5'11 P.-E. 800 Detector Dual flame Dual flame Dual flame Dual flame Dual flame Dual flame Flame Internal standard Cyclohexyl acetate Stationary phase support 10 per cent.PEG 400 Chromosorb W, 85 to 100 mesh Column- Length Diameter Material Tempera- ture/"C Injector tem- perature/"C Flow-rate of carrier gas (nitrogen) Chart speed/ Sample sizelpl in h-1 5 f t $ in Glass 90 On column 60 ml min-l 15 1.5 6 f t 4 in Stainless steel 90 250 40 ml min-l 30 1 2 m 2-2 mm Stainless steel 85 200 20 p.s.i. 18 0.2 6 f t t in Glass 85 On column 40 In1 min-1 (argon) 24 1 6 f t t in Glass 90 On column 9 p.s.i. 24 1 6 f t 6 f t 4 in Q in Stainless Stainless steel steel 90 90 200 110 20 p.s.i. 40 mi min-l 24 24 0.3 1 J Pye 104 Dual flame 5 ft + in Stainless steel 90 160 37 ml min-1 30 0.6 Appendix RECOMMENDED METHOD FOR THE DETERMINATION OF 1,s-CINEOLE IN OILS OF CARDAMOM, ROSEMARY, SAGE AND SPIKE LAVENDER (RANGE 10 TO 40 PER CENT.) BY GAS CHROMATOGRAPHY OPERATING CONDITIONS- It is essential that throughout a determination the operating conditions are maintained as constant as is practicable.It is also essential to use the detector - amplifier system within its linear range.17 Detector . . .. .. Stationary phase . . .. Support . . .. .. Column temperature . . .. Injection . . .. .. Gas flow-rates . . .. Chart speed . . .. .. Peak heights (internal stan- dard and cineole) . . . . Internal standard . . .. Stationary phase loading . . Column . . .. .. Cineole . . .. .. Solvent .. .. .. Sample size . . .. .. Flame ionisation. Poly(ethy1ene glycol) (PEG) 400. Chromosorb W. acid washed, silanised, 85 to 100 mesh. About 10 per cent. mlm. Length 6 feet; diameter 4 to t inch; glass or stainless steel.Isothermal, 90 "C maximum. On column, or if a pre-heater is used, maximum temperature 120 "C. To give satisfactory instrument performance. 15 inches per hour (minimum). Within 40 to 75 per cent. of full-scale deflection. Cyclohexyl acetate (purity by gas chromatography not less than 99.0 per cent.). Purity by gas chromatography not less than 99.0 per cent. Ethyl acetate. Such that the internal standard and cineole peaks fall within the linear range. DETERMINATION OF THE FACTOR, f, FOR THE INTERNAL STANDARD (CINEOLE = 1)- Make all weighings to an accuracy of 0.2 mg. Weigh about 0-25 g of cineole and 0.5 g of cyclohexyl acetate (or such other mass as will give about equal heights for the two peaks), and dilute them with 10 ml of solvent.InjectAugust, 19731 CHROMATOGRAPHY TO THE ANALYSIS OF ESSENTIAL OILS. PART 11 623 1.0 p1, or such other volume as will ensure response within the linear range, and calculate to three decimal places the factor, f , from the equation- h x d m, h, x dc m f=- X - where he is the height of the cineole peak; d, the retention distance of the cineole peak; h the height of the cyclohexyl acetate peak; d the retention distance of the cyclohexyl acetate peak; m the mass of cyclohexyl acetate; and m, the mass of cineole. Repeat twice on the same solution, and use the average of the three values off in the calculation of the cineole content of the sample. DETERMINATION OF THE CINEOLE CONTENT OF THE SAMPLE- Weigh an adequate amount of the sample (0.5 to 2.5 g, according to whether more or less cineole is present) and about 0.5 g of cyclohexyl acetate that will give about equal heights for the two peaks, and dilute with 10 ml of solvent.Inject about 1.0 pl, or such other volume as will ensure response within the linear range of the instrument, and calculate the cineole content of the sample to two decimal places from the equation- H e x D, M H x D Ms x - x 100 Cineole, per cent. = f x where f is the factor determined as described above; H , is the height of the cineole peak; Dc the retention distance of the cineole peak; H the height of the cyclohexyl acetate peak; D the retention distance of the cyclohexyl acetate peak; M the mass of cyclohexyl acetate; and M , the mass of sample. Repeat twice with the same solution and report the average of the three results to one decimal dace. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. REFERENCES Tedesko, E., Riv. Ital. Essenze, 1927, 9, 197. Kleber, C., and von Rechenberg, W., J . prakt. Chem., 1920, 101, 171. Cocking, T. T., Perfum. Essent. Oil Rec., 1920, 11, 281. Cross, A. H. J., Gunn, A. H., and Stevens, S. G. E., J . Pharm. Pharmac., 1957, 9, 841. Walker, G., J. Soc. Chem. Ind., Lond., 1923, 42, 497T. Gildemeister,”E., and Hoffman, F., “Die Atherrischen Ole,” Third Edition, Volume 1, Schimmel Baker, R. T., and Smith, H. G., “Eucalypts and Their Essential Oils,” Second Edition, Sydney, Martin, E. W., and Harrison, J. W. E., J . Amer. Pharm. Ass., Scient. Edn, 1950, 39, 677. Montes, A. I., An. Asoc. Quim. Argent., 1954, 42, 223. Naves, Y . R., Helv. Chim. Acta, 1945, 28, 1222. Presnell, A. K., J . SOG. Cosmet. Chem., 1953, 4, 101. Maennchen, K., J. Appl. Chem. Abstr., 1955, 5, 818. Analytical Methods Committee, Analyst, 1931, 56, 738. Jolly, S . C., Editor, “Official, Standardised and Recommended Methods of Analysis,” W. Heffer British Standard 2073 : 1962. Analytical Methods Committee, Analyst, 1971, 96, 887. Primavesi, G. R., McTaggart, N. G., Scott, C. G., Nelson, F., and Wirth, M. M., J . Inst. Petrol., NOTE-Reference 16 is to Part I of this series. and Co., Berlin, p. 665. 1921, p. 364. & Sons Ltd., Cambridge, 1963, p. 89. 1967, 53, 367 (Appendix 11, p. 377).

ISSN:0003-2654    

DOI:10.1039/AN9739800616

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年代:1973

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624 Book Reviews Analyst, August, 1973 ABSORPTION SPECTRA IN THE ULTRAVIOLET AND VISIBLE REGION. Edited by L. LLNG. Volume This volume takes the series to 3212 compounds. It contains spectra of a considerable range of substances but on this occasion the main emphasis is on heterocyclic compounds. There is a long series of pyrimidinone derivatives and among the other groups considered are pyrazines, pyridazines, quinoline and quinolone derivatives together with quinoxalines and quinolizines. Included also are some imidazole, thymine, uracil and tryptophan derivatives. In most instances, spectra in two solvents are recorded and, when appropriate, in acidic and alkaline media. R. A. MORTON XVII. Pp. 400 (loose-leaf). Budapest : Akadkmiai Kiadb. 1972. Price f17. The high standard of the series is maintained.ENVIRONMENTAL MERCURY CONTAMINATION. Edited by ROLF HARTUNG and BERTRAM D. DIN- MAN. Pp. x + 349. Ann Arbor, Michigan: Ann Arbor Science Publishers Inc. 1972. Price i9.40. Any information concerning the distribution of a heavy metal in the environment is very welcome, especially when that metal is as toxic or as topical as mercury. This book is admirable in that it states the problems involved and gives many examples of work undertaken and makes it clear that a great deal of work still has to be done, and also that better analytical techniques need to be achieved, particularly for very low levels of mercury. In the first part, the occurrence of mercury in the environment and man is described, together with the various ways in which mercury is released into the environment.Special attention is given to results of work in areas where the release of mercury is or was high, such as the Great Lakes in America and Minimata in Japan. The analyses are mainly of water, fish, birds and humans. The second part describes the methods of analysis that have been suggested or used, the first half of which contains a very comprehensive review with thirty-two pages of references. The second half gives a series of short accounts of promising analytical methods applied to real samples, including the use of neutron-activation analysis for determining total mercury. This section underlines the usefulness of round-robin sample surveys and the need for more standard reference materials. In the third part, the environmental dynamics of mercury are discussed.The questions asked are-When the various forms of mercury are released, where do they finish up ? What chemical transformations are there ? Thus topics such as methylation of mercury, interaction with food chains and adsorption - release from soils are given in some detail. In the fourth part, the biological effects of mercury compounds are presented. This very important section contains a detailed account of the effect and distribution of methyl- mercury in humans and other animals during the terrible Minimata incident. It also contains a survey on people subjected to chronic exposure to inorganic mercury from an industrial plant. Work on attempts to correlate dose - response relationships and to arrive at toxicity limits are included, with interesting comments on the possibility of detecting sub-clinical effects of mercury ingestion.Frankly, this is a good book that can be recommended in spite of its very high cost. The only criticism that may be levelled is that the data are based on a conference held in 1970 while we are now in 1973. G. NICKLESS The book can be divided into four parts. METALLURGICAL STEREOGRAPHIC PROJECTIONS. By J. S. SMAILL. Pp. viii + 262. London: This book is based on a computer program developed to aid structure identification by electron diffraction with the electron microscope. Stereographic projections (162 in all) are given in Chapter 5 for the structures of the common metals and metal oxides, carbides, nitrides and sulphides. It is claimed that the program is not restricted to metallurgical structures but is completely general in application and could be applied to mineralogical structures. The program is capable of generating stereographic structure about any given pole direction or pole plane. The book would be of some interest to specialists in X-ray analysis and those who use the A.S.T.M. powder diffraction file. Adam Hilger Ltd. 1972. Price i 7 . V. J . JENNINGS

ISSN:0003-2654    

DOI:10.1039/AN9739800624

出版商:RSC    

年代:1973

数据来源: RSC