CLINICAL TOXICOLOGY 11( 2 ) , pp. 237-243 ( 1977)

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

Blood Lead Analysis-Lead Loss to Storage Containers

BRIAN C. UNGER, B.A. and VERNON A. GREEN, Ph.D. The Children's Mercy Hospital Toxicology Department Kansas City, Missouri

The introduction and development of flameless atomic absorption spectrophotometry has enabled detection of t r a c e metals in the ppb and sub-ppb range. Being able to m e a s u r e t r a c e elements a t such low levels s e e m s to have created s o m e unique problems which do not confront workers concerned with analyses of m o r e concentrated samples. A fundamental problem is the l o s s of metallic ions to cont a i n e r surfaces due to adsorption, which can strongly influence both the accuracy and the reproducibility of data. Issaq and Zielinski [l] studied the adsorption of lead in aqueous solutions s t o r e d in P y r e x and Kimax g l a s s and polyethylene containers and observed d e c r e a s e s in lead concentrations with time. Rosain and Wai [2] discussed the l o s s rate of m e r c u r y from aqueous solutions s t o r e d in polyethylene, polyvinyl chloride, and soft glass. Others [3-51 have studied the adsorption of m e r c u r y by the s u r f a c e s of various containers from aqueous solutions. Robertson [6] studied the adsorption behavior of t r a c e minerals in s e a water and concluded that s e r i o u s l o s s e s of indium, scandium, iron, s i l v e r , uranium, and cobalt can o c c u r by adsorption onto container surfaces. Riley [7] has suggested s e v e r a l reasons f o r the adsorptive properties of g l a s s and plastic surfaces. Using flameless atomic absorption spectrophotometry and the standard-addition technique for blood lead analysis, in o u r laboratory, we observed d e c r e a s e s in lead concentrations with time. This

237 Copyright 0 1977 hy MarLel Dekker. Inc All Rights Reserved Neither this work nor any part may he reproducedor transmitted in any form or by any meahs. electronic or mechanical. including photocopying. microfilming. and recording. or by any information storage and retrieval system. without permission in writing from the publisher

238

UNGER AND GREEN

work describes the lead l o s s as being directly related to the type of container material. Further, a discussion on the inhibition of lead l os s to container surfaces by nitric acid and hydrogen peroxide is presented. EXPERIMENTAL

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

Apparatus A Varian Techtron Model 1200 atomic absorption spectrophotometer equipped with a deuterium background co rre c t o r , a rapid response s t r i p chart r ecord er, and Varian lead hollow cathode lamp was used fo r this study. The burner assembly was replaced by a Varian Model 63 Carbon Rod Atomizer graphite furnace without further modification. All containers were pre-cleaned with concentrated nitric acid followed by five r ins es with deionized-glass distilled water. Oxford microliter pipets with disposable plastic tips were used f o r sample introduction.

Reagents and Materials All reagents were of analytical grade. Deionized glass-distilled water was used for all lead standard preparations. The stock lead nitrate solution was a 1000 ppm (1000 pg/ml) certified atomic absorption standard obtained from Fisher Scientific. Heparinized whole blood collected and stored in lead-free polyethylene bags was pooled and subsequently used in the standard-addition method f o r blood lead analysis. Intermediate Standards A range of standard solutions were prepared by pipeting the appropriate quantity of the stock solution into the appropriate container, which was then accurately brought to volume with deionized glassdistilled water. The sample containers were 25-ml volumetric flasks of Pyr ex brand ( F i s h e r Scientific) and 125-ml polyethylene bottles ( F i s h e r Scientific). The range of standards included: blank, 100 ppb, 250 ppb, 500 ppb, 750 ppb, and 1000 ppb or blank,

10 pg%, 25 pg%, 50 pg%,

75 pg%, and 100 pg%

BLOODLEADANALYSIS

239

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

Procedure The spectrophotometer was operated at an absorption line of 217.0 nm with a lamp current of 5 mA and a 1.0-mm slitwidth. T e s t sample preparation was a simple dilution accomplished by combining equal p a r t s of heparinized whole blood (0.5 ml), 5% Triton X- 100 ( 0 .5 m l ) , and the appropriate aqueous standard (0.5 ml ) in a 2.0-ml disposable plastic beaker ( F i s h e r Scientific). A 1.0-p1 aliquot of the test s a m p l e was then introduced into the graphite tube furnace. T h e Carbon Rod Atomizer (CRA) settings were (voltage setting/time setting-sec) d r y - 1.75/25, ash- 5.25/25, and atomize- 5.0/3.5. The graphite furnace was operated with a nitrogen purge and a water flow of approximately 1.0 liter/min. Standard graphite tubes were employed. R E S U L T S AND DISCUSSION Tables 1 and 2 show the percent l o s s of lead due to adsorption from a range of lead aqueous solutions which were stored in P y r e x g l a s s and polyethylene containers. Figures 1 and 2 are a graphic representation of the data presented in Tables 1 and 2. It s e e m s to be evident from the range of values obtained that adsorptive c h a r a c t e r i s t i c s not only vary from container to container as suggested by Issaq and Zielins k i [ l ] , but als o differ in degree from concentration to concentration. Loss from aqueous solutions stored in P y r e x glass was of notable interest. After 10 min, a 22% adsorption occurred, at 45 min, 32% w a s adsorbed, and at the end of five days a 52% lo s s was measured. Although the lo s s of lead was initially lower in the polyethylene containers, a s i m i l a r lo s s was noted over the en t i re five-day period. The rate of lo s s was determined by the equation of L = (y-b)/m, where L is the percent loss, m the slope, y the absorbance reading, and b the y intercept. Linear regression cu rv es were used to establish the slope and y-intercept values for each initial range of solutions. Linear regression cu rv es gave the highest correlation coefficients of the t hr ee equation f orm s attempted ( P y r e x glass: 0.994, polyethylene: 0.988). Absorbance readings fo r each range of test s a m p l e s obtained f o r subsequent time intervals were used to calculate correlation coefficients and rate of loss. Issaq and Zielinski [l] reported that 30% of the lead in aqueous solutions s to red in Py rex and Kimax g l as s was adsorbed a f t e r 5 min and that approximately 50% l o s s occurred after 1 hr. They a l s o obser ved loss of lead to polyethylene containers with 10% l o s s a f t e r 1 5 min and 30% af ter 90 min, and suggested the necessity f o r inhibiting such losses. Rosain and Wai [2] reported that l o s s e s of m e r c u r y w e r e

UNGER AND GREEN

240

TABLE 1. L o s s of Lead from Standards Stored in P y r e x Glass Containers

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

Loss, %a Time

Aqueous

10 min

22

4

2 0 min

23

6

30 min

28

9

4 5 min

Second day

32 36

13 11

Third day

45

8

Fourth day

47

4

Fifth day

52

7

1.0% HN03

3%

H202

a Mean of five different concentrations (10, 25, 50, 75, and 100 CLg%b). TABLE 2. L o s s of Lead from Standards Stored in Polyethylene Containers

Loss, %a Time

Aqueous

1.0% HNOJ

10 min

4

4

2 0 min

9

6

30 min

17

9

4 5 min

24

15

Second day

30

14

Third day

42

15

Fourth day

45

14

Fifth day

52

16

a

3% HzOr

Mean of five different concentrations (10, 25, 50, 75, and 100

CLg%).

BLOOD LEAD ANALYSIS

24 1

100

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

75

i 3 50

:

25

- - _ _ _ -- -__

4

0

I I-1 10

30

20

I

45

I

I

I

I

2

3

4

5

Days

Minutes TIME

FIG. 1. L o s s of lead from standards s t o r e d in P y r e x glass.

not observed a f t e r 100 h r of storage when solutions w e r e acidified to pH 0.5 with nitric acid. Even though the u s e of nitric acid has been suggested as the most p r e f e r r e d preservative, i t s removal of metallic impusities from container s u r f a c e s [8- 101 presents an additional problem. Issaq and Zielinski [ 11 observed that hydrogen peroxide and nitric acid a r e both good preservatives f o r aqueous solutions containing t r a c e lead ions. Poor desorptive properties of HzOz s e e m s advantageous over HN03 as a preservative f o r t r a c e lead solutions. In addition to the l o s s e s measured from aqueous solutions, Tables 1 and 2 show values obtained f o r lead solutions that w e r e treated with both nitric acid ( 1%)and hydrogen peroxide (3%). These solutions w e r e derived by adding the appropriate quantity of stock solution to a s a m p l e container containing a prepared 1.0% HNOs o r 3.0% HzOz solution. Figures 1 and 2 reflect a comparison of the l o s s e s of the

UNGERANDGREEN

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

242

.-

I

0 I

10

I

I

30

20

Minutes

I

65

I

I

2

3

I

4

r

5

Days

TIME

FIG. 2. Loss of lead from standards s t o r e d in polyethylene. three s y s t e m s studied. It s e e m s readily apparent that both p r e s e r v a tives reduce the l o s s of t r a c e lead ions from solution. However, the stability of the HzOz s e e m s to be higher f o r both P y r e x glass and polyethylene o v e r the t i m e period of five days. Having measured these lead l o s s e s by the standard-addition method of blood lead analysis, we suggest that the l o s s to container s u r f a c e s used f o r aqueous standard s t o r a g e t r a n s l a t e s through the m a t r i x of whole blood. Since this loss is quite apparent, inhibition of the loss to containers using hydrogen peroxide, nitric acid, o r other effective preservative is essential for meaningful quantitative analyses of lead a t t r a c e levels. Explanation and understanding of the inhibition mechanism a r e yet to be fully uncovered. Additional study is needed f o r a better understanding of the loss and the inhibition of l o s s of t r a c e lead solutions to s t o r a g e containers.

BLOOD LEAD ANALYSIS

243

Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For personal use only.

R E F E R E N C ES

H. J. I s s a q and W. L. Zielinski, Jr., Anal. Chem., 46, 1328 (1974). R. M. Rosain and C. M. Wai, Anal. Chim. Acta, 65, 279 (1973). P. Benes and I. Rajman, Collect Czech. Chem. Commun., 34, 1375 (1969). P. Benes, Collect Czech. Chem. Commun., 35, 1349 (1970). R. V. Coyne and J. A. Collins, Anal. Chem., 44, 1093 (1972). D. E. Robertson, Anal. Chim. Acta, 42, 533 (1968). J. P. Riley and G. Skirrow, C h e m i c a r o c e a n o g r a p h y , Vol. 2, Academic, London and New York, 1965, p. 303. D. E. Robertson, Anal. Chem., 40, 1067 (1968). E. C. Kuehner and D. H. F r e e m a n , Purification of Inorganic and Organic Materials (M. Zief, ed.), Dekker, New York, 1969, p. 297. E. C. Kuehner, R. Alvarez, P. J. Paulsen, and T. J. Murphy, 44, 2050 (1972). Anal. Chem., -

Blood lead analysis--lead loss to storage containers.

CLINICAL TOXICOLOGY 11( 2 ) , pp. 237-243 ( 1977) Clinical Toxicology Downloaded from informahealthcare.com by Stanford University on 11/19/14 For pe...
266KB Sizes 0 Downloads 0 Views