Document o9KyG4p36kRb2JkwmxMejdkJ8

''*?54S -'??-'. A ft y -COKMEKTS O ^ RBPORT LTD-li.5-57 (December ll|, 191+5) ;h - V .^ 4 t ;-r - _ *r djH/1 "cannot agree entirely with the contents or conclusions contained.in this report, be have tested the "one color" method of thoB'4tdh:Rouge Labors toi'y thoroughly and. we were so convinced of its advantages that we have incorporated this stop in our routine method, we have made approximately 1+.,000 unalysos with it axid we are completely satisfied with the results. . 1. we find no losses at low lead concentrations. 2 We find the final single color to be as stable as the mixed color which v/e used previously. 3. We find no losses 'due to phosphate in the final extraction even though citrate is not added. Experiments on this phase were carried out by us with quantities of phosphate up to 5 mg. This quantity is excessive and is unlikely to occur in the last extraction if good technique is employed in previous steps. Phosphate, in KCIi has boon a topic of discussion for many years, but the amount in this roiigent is so small that in our laboratory we have not bothered to remove it. Fore serious is entrainment of phosphate in the final step due to incomplete washing of extracts in the earlier extractions. We have stressed this point 'as well as the need for proper sequence in adding the reagents in the last step in 3avoral of our publications. The addition of citrate in the estimation extraction is unnecessary although we recommend its use in the initial extraction step. 4 I admit failure to understand the tests described on pa.:es i| and 5 under ''Solubility of lead dithizonate at pH 11.i^." Wo have tested this angle comparatively using 100 micrograms of lead and extracting with a single quantity of dithizon at pH 9*5 and 11,5 The aqueous phase was then analysed for load b y extract ing it with di-beta-naphthylthiocarbaaone, which extracts completely at high pH values and is completely insoluble in the aqueous phase. Comparable quantities (1-2 raicrogr&ms) were found. V felt that this represented entrainment losses rather than solubility losses. . } Accuracies of 7*5 per,-cent shown on page are excellent for tho range 0-5 micrograms,.particularly in a 1 cm. cell. In most} analytical work, including this type, errors up to 20 per cent are permissible in'the range 0-5 micrograms. - 6,.', The comments on aging-of reagents are generally recognized by analysts and, alX that" is, required is a blank deter mination in the final e x t r a c t i o n'so as to establish the zero value of the curve. The calibration curve is then}drawn parallel to tho original and the values of subsequent readings employing the same dithizone solution are taken/frorngthe corrected curve. This may be eliminated if the zero is established by setting the photometer to 100 with the blank in both cells. O O C o S i 'O Commenta-oft Report LTD~U5~57 continued - 2- 7 . `' * It is ^ d e c i d e d advantage to be able to use one dlthlssobe solution for all extractions, Initial and final colorimetric and this feature attracted us to the method since it meant the ifelimiii*tiohi of bottling three distinctly different solutions which might go bad and whioh might delay analysis if they had to be made up and calibrated. Pit It should be admitted that the Baton Hcuge method is applicable only to pure lead solutions, \ihen applied to biological material, it must be modified to handle this more complex medium which may contain interfering laments, particularly bismuth. This has been done in our laboratory and the modified procedure discussing all of the points mentioned in the LTD**I|,5'**57 report will be published as a follow up to the paper by Snyder# 9* In connection with the TSL test, it should be pointed out that regardless of fchs compound which is formed with iodine and dithizona, it is interesting that this compound is different from lead dithizon as evidenced by the shift of the maximum to lower wave length (ij.90 against 510). As used by Baton Rouge, the method is not a "single color" method but rather a "mixed colorM because of the great exceps of dithizon which is employed. This excess is important 8lnce`/thQ amount of dlthlzone in the extracting solution is reduced to one-half (to conform to the original single color method); quantities of lead below J micrograms are not extracted. 10. On page 8, the statement is made that sensitivity was *lost due to the coincidence of th absorption maxima of the dithizon reagent and the org&no-lead dithizonate." Dlthlzone transmits strongly at I4.9O upj in fact, it shows a. transmission maxlrous at 505 b p * Its absorption maxima occur at 610 JOjlt mb and 11. It is recognized that the pH 1 1 .5 extraction method is so contrary to what has been done with dlthlzone in the past that there may be some resistance to its use. e are convinced of its superiority over the older method, but also recognize that difficulties might ooeur in the appliestion.of the method to specific problems. It is understood therefore that each application should be thoroughly investigated and that certain modifications may become, necessary# - :, J. Cholak January 5 19M> K e 0005381