Analyst, April, 1973, Vol. 98, pp. 243-245 243 - - - - - - An Improved Method for the Determination of Whole Blood Lead by Using an Atomic-absorption Technique -0 10 20 30 CI s - 4 0 2 W n 3 -60 C e! t- -50 .E ‘5 70 80 90 BY G. ALAN ROSE AND ELIZABETH G. WILLDEN (Department of Pathology, St. Peter’s Hospitals, Endell Street, London, W.C.2) I The Delves technique for measuring whole blood lead has been con- siderably improved by wet ashing with aqua regia instead of simply drying with hydrogen peroxide. Smoke is eliminated, and the reproducibility of the method is improved. VJ IN a recent survey, Keppler et a2.l found that less than half of the clinical laboratories that were reported to be undertaking blood lead determinations were doing so with a reasonable degree of accuracy.This situation was improved by Delves,* who used atomic-absorption techniques in conjunction with what is now called the “Delves technique.” In this method whole blood was placed in a cup together with 100-volume hydrogen peroxide and, after drying the mixture, the cup was introduced directly into an air - acetylene flame with an absorption tube assembly attached. Unfortunately, the recorded smoke trace produced when using Delves’ method can be very misleading and difficulties in the interpretation of the results can lead to inaccuracies. N Pb 1 Y 1 @ SAC and the authors.244 ROSE AND WILLDEN : IMPROVED METHOD FOR THE DETERMINATION [Analyst, VOl. 98 We have found considerable advantages in using aqua regia instead of hydrogen peroxide. Firstly, the smoke produced on introduction of the sample can be eliminated, and secondly, the reproducibility can be greatly increased.The original tube and cups, which were made of nickel, had to be replaced by similar apparatus made of fused quartz (obtainable from Thermal Syndicate Limited, Wallsend-on-Tyne) . In each instance, 0.010 ml of blood was subjected to wet ashing by adding the aqua regia and evaporating to dryness on a hot-plate, care being taken to avoid spluttering. Measurements were carried out on a Perkin-Elmer 290B spectrophotometer with the modified Delves’ absorption tube attachment. Results obtained by use of the Delves technique, in which whole blood (0.010 ml) and 100-volume hydrogen peroxide (0.020 ml) were mixed together in the cup, have been compared with our results, which were obtained by using aqua regia instead of hydrogen peroxide. As can be seen from Fig.1, the two methods give comparable results, but the interpretation of the results was facilitated, and their reproducibility considerably enhanced, by using our improved method. It will be noted that when 0.600 ml of aqua regia is added to the sample, the smoke traces are very small, and are negligible with 0.800 ml. Different volumes of aqua regia were tried. I - TABLE I COMPARISON OF RESULTS OBTAINED BY USING THE TWO METHODS ON REPLICATE BLOOD SAMPLES Number Mean/ Range/ Standard Method of assays pg per 100 ml pg per 100 ml deviation Delves’ method(with the original matched cups) 15 09-26 59 to 79 4.32 Delves’ method (with quartz cups) . . . . 15 67-1 3 47 to 79 8.96 Aqua regia method (with matched cups) .. 20 08-25 64 to 72 2.49 Aqua regia method (with unmatched cups) . . 20 08-60 60 to 77.5 4.93 10 20 c; f 30- 0 L 40- c .$ 50 m .- $, 60- $ 70- C m 80 90 A blood sample with a high lead content was examined by the two methods and the results subjected to statistical analysis. The comparison is shown in Table I, from which it can be seen that oxidation of the blood with hydrogen peroxide is unsatisfactory when the quartz cups are used. The aqua regia method with unmatched quartz cups is almost as accurate as the original Delves method with matched nickel cups, but is considerably improved when the quartz cups are matched in terms of length of time in use. - - - - - A 01 ~ 75 50 25 100 I 75 50 25 Pb concentration/pg per 100 ml Fig. 2.Comparison of pure lead stan- dards, with (peaks A) and without (peaks B) added electrolytesApril, 19731 245 Fig. 2 shows typical peaks for pure lead standards over the range required for deter- minations on whole blood samples, both with and without addition of electrolytes at levels comparable with those found in whole blood. The differences between the two sets of results are very small and can be attributed to normal experimental errors. Calibration graphs of aqueous standards and of whole blood containing increasing amounts of lead are shown in Fig. 3. This method of addition, involving the use of whole blood of known lead content spiked with various amounts of lead solution, gave very similar results to those obtained with the aqueous solutions.Thus, the two lines are almost parallel and the error introduced by the deviation from absolute parallelism was 3 per cent., i.e., recoveries of added lead were 100 -j= 3 per cent. OF WHOLE BLOOD LEAD BY USING AN ATOMIC-ABSORPTION TECHNIQUE D Added lead content / pg per 100 ml Fig. 3. Comparison of whole blood and aqueous lead standards. A, whole blood with added lead standards; and B, aqueous standards In order to establish that the smoke was being removed satisfactorily, measurements were taken on a nearby non-resonant wavelength by using blood with a lead content of 50 pg per 100 ml. An absorption signal equivalent to 3 to 5 pg per 100 ml was obtained. Thus, the non-specific absorption accounts for up to 10 per cent. of the whole blood lead. This value compares favourably with that found by Delves’ original method.2 The method has proved to be reliable for whole blood lead values both in the normal and the abnormally high ranges. The equipment was donated by the Institute of Urology, London. REFERENCES 1. 2. Keppler, J. F., Maxfield, M. E., Moss, W. D., Tietjen, G., and Linch, A. L., Amer. Ind. Hyg. Delves, H. T., Analyst, 1970, 95, 431. Received April 27th, 1972 Acccpted November 21st, 1972 Ass. J., 1970, 31, 412.