Determination of antimony and tellurium in human blood by

Walter J. Boyko , Peter N. Keliher , and James M. Malloy. Analytical Chemistry 1980 52 (5), 53- ... A. T. Zander , G. M. Hieftje. Applied Spectroscopy...
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979

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Determination of Antimony and Tellurium in Human Blood by Microwave Induced Emission Spectrometry P. F. E. van Montfort,‘ Jacob Agterdenbos, and B. A. H. G. Jutte Analytisch Chemisch Laboratorium, Croesestraat 77A, Utrecht, The Netherlands

The use of the EDL (electrodeless discharge lamp) emission method for the determination of Sb and Te in natural human blood is described. A dried 1-mL blood sample is ashed by microwave excited oxygen and the ash dissolved by refluxing with 0.1 M HCI. The bulk of the salts remaining from the blood sample are removed by an extraction-reextraction procedure and flnally an aliquot (e.g. 100 pL) of the final aqueous reextract is analyzed by the EDL emission method. Recoveries of the various steps in the procedure have been checked radiochemically for Sb. Results are presented for Sb (from 34 samples) and Te (from 7 samples). Normal values are about 1 ng/mL for Sb and 0.25 ng/mL for Te.

acidified aqueous phase, which is required for the EDL method. Reduction of antimony to the trivalent state after ashing is required for the extraction procedure. In case of Te, no reduction is necessary. Both for the total procedure and for the extractionreextraction step “spectroscopical” recovery experiments on both elements were performed. More detailed information on Sb was obtained radiochemically. The total time required for an analysis is about 2 h; each of the steps (drying the sample, ashing, and extraction-reextraction) takes about 20 min and 1 h is needed for the preparation of the EDL and its measurement.

EXPERIMENTAL The purpose of the present work was to show the applicability of the EDL (electrodeless discharge lamp) emission method to complex materials. We selected the determination of Sb and Te in natural human blood for the following reasons. (i). The determination of the natural T e and Sb content in human blood has not been described before, presumably for lack of good analytical procedures. (ii). There is a suspicion of some correlation between the content of these elements in blood and certain diseases or biochemical processes in the human body. (iii). It would be useful to be able to analyze a natural Te- or Sb-content in blood in certain cases of poisoning. The EDL emission method involved in this work is based on the philosophy that the detection power of analytical spectrometry is limited by dilution of the sample after its introduction into an excitation source or an atomization cell such as a flame, a plasma jet, or an arc. T o prevent this dilution, the sample is sealed into a small quartz bulb. Exposure of the sealed sample to a microwave field (2450 MHz) results in the emission of line spectra of the elements present in the bulb (1-5). An excitation buffer and a few Torr of hydrogen or a noble gas are added into the bulb before sealing, however, to control the excitation conditions. Using pure salt solutions, the following detection limits were obtained (all expressed in ng/mL = ppb): As, 1;Sb, 0.02; Zn and Cd, 5.10”; In, Pb, and T1, and Te, (1-5). Values given are the best obtained until now; they depend on the nature of the excitation buffer applied. Application of the method to some simple matrices has been described ( I , 3). Earlier investigations showed a serious interference in the determination of a few nanograms or picograms of an element by organic or inorganic interfering compounds also present in the EDL. T o overcome these interferences the blood samples have to be ashed and the analyte elements have to be separated from the salts remaining from the blood samples after ashing. The dried blood sample is ashed with microwave excited oxygen. This procedure is based on the work of Kaiser e t al. (7). After dissolution of the ash, the separation is achieved by an extraction-reextraction procedure in which the analyte element is extracted into an organic phase as described by Bode and Neumann (6) and reextracted into a 0003-2700/79/0351-1553$01 .OO/O

Apparatus. On a vacuum line, as described previously ( I , 21, six EDLs can be prepared simultaneously. The microwave field was generated by an EMS Microtron 200 MK I11 microwave generator and fed to the EMS 216L microwave cavity used for the measurements. Except for the measurement of Te with K1 as an excitation buffer, the incident microwave power was monitored using a Bendix Micromatch power meter model 725N4. It should be noted that the EMS and the Rendix readings differ considerably (8). For the destruction with microwave excited oxygen, an EMS 200 MK I1 microwave generator together with an EMS 216 L cavity were used. The ashing apparatus is shown in Figure 1. It was connected to an Edwards EDM 12 vacuum pump. Measurements were made using the monochromator of either a Varian AA4 atomic absorption spectrometer or of a Unicam SP 500 spectrophotometer, both equipped with a Hamamatsu R106 photomultiplier. Vitreosil quartz from Thermal Syndicate was used in preparing the EDLs. For the extraction, silica separatory funnels (volume 10 mL) with PTFE taps were applied. Radioactivity measurements were made with a Philips PW4631-PW4620 ?-counter. Instrument Settings. The cavities were tuned to minimum reflected power, both during ashing and measurement. During ashing a net power (incident minus reflected) of 100 W was applied. All measurements for Te were made with 50-W net power except on the experiments with the KI excitation buffer. In the latter case we used 65 U’, the same net power that was used in the Sb measurements. The spectral bandwidth of the monochromators was in all cases about 0.1 nm. The measurements on blood samples were made with maximum scale expansion. All signals were corrected for a background signal, measured immediately afterward at a wavelength 0.3 nm above the analyte lines (Te: 238.6 nm and Sb: 287.8 nm). Reagents. Suprapur quality HC1 (Merck,Darmstadt) was used t o acidify the aqueous solutions. In all experiments bidistilled water was used for the dilutions. Te and Sb solutions were prepared by dissolving the high purity metals (Koch Light) in aqua regia. The Bi13-CsIexcitation buffer was prepared as follows: dissolve 115 mg of Bi203(Specpure, Johnson and Matthey) in 10 mL of 10 M HCl, add 195 mg of CsI (Suprapur, Merck) and dilute to 100 mL. From this 100 mL, 10 mL is pipetted into a 100-mL volumetric flask. To this 10 mL of 7 M HI (Suprapur, Merck) is added and the solution is made up to 100 mL with water. Into each EDL, 25 gL of this final solution is pipetted as an excitation buffer; Le., each EDL contains 2.5 Fg of Bi and 2.5 ,ug of Cs. The excitation buffer stock solution has to be replaced every two or C 1979 American Chemical Society

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ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979

Table I. Metal Concentrations in Human Blood; a “Synthetic Blood Salt” Solution concn., metal mg/L added as P 1150 NaH,P0;2H20 (Baker A.R.) 50 S (Fluka p.a.1 Na,SO, NaCl Na 2000 (Baker A.K.) K 3800 KCl (Baker A.R.) Ca 60 CaCl;GH,O (Fluka purum) A1 0.14 AICI, (Baker A.R.) Pb 0.22 PbCl, (Fluka p.a.) Fe 500 FeC1,.6H20 (Fluka purum) cu 1 CUCI,.~H,O (Baker A.R.) Zn 10 ZnC1, (Fluka p.a.) mL (for Sb) of 0.1 M HC1 is pipetted into the destruction tube and the ash is dissolved under reflux under atmospheric pressure, heating the solution with 100-W microwave power without ignition of a plasma. ( b )Reduction. In order to reduce all Sb to the trivalent state, IC mL of the Sb-solution is combined with 0 . 0 4 ~mL of the reduction solution and the solution obtained is heated to boil for 5 min. After this procedure the Sb can be extracted by the extraction procedure. ( c ) Extraction and Reextraction. Three mL in the case of Te or 5 mL in the case of Sb of the 0.1 M HC1 solution of Te or Sb (either directly prepared from a more concentrated solution or from the resulting solution after ashing a blood sample) are shaken for 5 min with 5 mL of a solution containing 8 pg of DaDTC/mL of tetrachloromethane. After separation the organic layer is transferred into a separatory funnel containing 1.5 mL (for Te) or 5 mL (for Sb) of a solution of 15 pg of Cu2+/mLof 0.1 M HC1. After shaking for 5 min and settling of the phases, both phases are centrifuged at 2400 rpm for 5 min. After this, an aliquot (e.g. 100 pL) of the aqueous phase is transferred into the EDL with a micropipet. ( d ) Preparation of EDLs, Measurement, and Interferences. Into a empty EDL is introduced e.g. 100 pL of the analyte solution Figure 1. Microwave excited 0, ashing apparatus and 25 pL of the solution containing the BiI,-CsI or the KI excitation buffer is added. The EDL is frozen to dryness, filler gas (HJ is added to 5 Torr for Te or 2.5 Torr for Sb, and the EDL three months because of the oxidation of HI on standing. The alternative KI excitation buffer, containing 2 mg of KI/mL, is sealed off with a propane-oxygen flame. Finally the EDL is was prepared by dissolving KI (Suprapur, Merck) in bidistilled placed into the microwave cavity and the appropriate power is applied. water. The tetrachloromethane (BDH, Analar, and Baker, BAR) was Interferences were investigated by measurements on EELS containing 1 ng of Te or 80 pg of Sb as analyte, 50 pg of KI, purified by distillation, followed by extraction with 1M of HC1. respectively, 2.5 pg of Bi and 2.5 pg of Cs (as iodides) as excitation For the reextraction 20 mg of high purity CuO (Koch Light) was dissolved in 1 L of 1 M HC1. Diethylammonium-N,N-diethyl- buffer, and with varying amounts (25 ng to 10 pg) of interfering metals. In addition the interference by various amounts (0.1 to dithiocarbamate (DaDTC) (p.a., Merck) was, just before use, 5 pg) of organic matter in the determination of 2 ng of In (with dissolved in purified tetrachloromethane and diluted to the the Bi1,-CsI excitation buffer was measured). appropriate concentration. The reduction solution for the re( e ) Radiochemical Experiments. One mCi of carrierfree :i5Sb duction of Sb to the trivalent state is prepared daily by dissolution (NEN Chemicals), i.e. about 1pg of pure radioactive lz5Sb,was of 0.75 g of ascorbic acid (p.a., Merck) and 1.5 g of KI (Suprapur, dissolved into 1 mL of 0.1 M HCl. To this solution 100 pg of Merck) in 10 mL of bidistilled water. A synthetic blood salt inactive Sb were added. The resulting Sb stock solution (Sb*) solution was prepared as described in Table I. was used in the recovery studies A-F. Procedure. The following sub-procedures have to be described (A) The extraction-reextraction procedure was checked ra(a) Drying, ashing, and dissolution; (b) Reduction of the analyte diochemically for pure Sb solutions, including the reduction step. (Sb only); (c) Extraction into tetrachloromethane and reextraction For this purpose 25 pL of the Sb* solution were added to 50 mL into water; (d) Preparation of EDLs, including measurement and of 0.1 M HCl. After reduction by the procedure described above interferences; (e) Radiochemical experiments. Each of these at b, 50 pL of the resulting solution are pipetted into a separatory sub-procedures will be dealt with in detail. funnel and the extraction-reextraction procedure described at ( a ) Ashing. About 1 mL of human blood is dried under an c is performed. infrared lamp. The dried sample is transferred to the bottom (B) The procedure described at A was carried through with of the destruction tube of the ashing apparatus (Figure 1). The 25 mL of 0.1 M HCl and 25 mL of the synthetic blood salt solution cavity is placed just over the dried sample in the tube, the asher instead of 50 mL of 0.1 M HCl, thus giving overall recovery data is evacuated to 0.01 Torr and the plasma is ignited at 100-W net on the reduction procedure for blood salt solutions. power by means of a Tesla coil. A stream of oxygen is transmitted (C) The recovery of the extraction-reextraction procedure from through the asher to give a pressure of about 3 Torr (400 Pa). blood salt solutions was checked after reduction of Sb. For this This stream is maintained throughout the ashing procedure. 25 pL of the Sb* solution were added to 50 mL of 0.1 M HCl and During the ashing procedure the cavity is moved downward, the reduction was carried through. From the resulting solution, causing the lower part of the plasma to touch lightly the upper 50 pL were transferred into a separatory funnel containing 2.5 part of the sample. The inner tube of the asher is water cooled mL of 0.1 M HCl and 2.5 mL of the synthetic blood salt solution as shown in Figure 1. A dried blood sample is ashed completely and the extraction-reextraction was performed. as an average in about 20 min, leaving a white ash. The asher is brought to atmospheric pressure, opened, 3 mL (for Te) or 5 (D) To check the overall recovery of the reduction and the

u

ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979

extraction-reextraction procedure in a blood salt medium 25 pL of the Sb* solution were added to 50 mL of 0.1 M HC1. From the resulting solution, 50 1L were transferred into a test tube containing 2.5 mL of XCl and 2.5 mL of the synthetic blood salt solution. After reduction the solution is transferred into a separatory funnel and the extraction-reextraction is carried through. In all recovery experiments.the overall y activity was measured in cpm for: (i) the empty tube, Le., the background ( a cprn); (ii) 1 mL of the organic phase ( F , cpm); (iii) 1 mL of the original aqueous phase ( F , cpm); (iv) 1 mL of a reference solution made by the same dilution procedure of Sb* as described at A to D but without extraction-reextraction ( r cpm); and (v) 1 mL of the final aqueous phase after reextraction (x cpm). The recovery of the total procedure is then given by the relation: (x - a ) / ( r - a ) X 100%. (E) The recovery of the ashing procedure was traced by adding 50 ~ LofL the Sb* solution (Le., 2.5 ng Sb) to 1.5m1, of blood. After ashing, the ash is dissolved in 5 mL of 0.1 M HC1 under reflux. The activity of 1 mL of the resulting solution is measured and compared with 1 mL of a reference solution, made from the Sb* solution by the same dilution procedure but without ashing and refluxing. (F) The overall recovery was checked by adding 50 pL of the Sb* solution to 1.5 mL of blood. After the ashing, reduction, and extraction-reextraction procedure, the 7 activity of 1 mL of the final aqueous phase is compared with the 7 activity of 1 mL of a reference solution.

RESULTS AND DISCUSSION In this section, the subprocedures are discussed first. The radiochemical experiments will be discussed separately. (a) Ashing Procedure. A wet destruction gives rise to two major difficulties: Contamination by the chemicals used and interference by the resulting high salt concentrations. Therefore we applied the dry ashing described by Kaiser et al. (7). A stream of oxygen is passed through a 2450-hIH1 plasma, activated, and the activated oxygen is used for the destruction of the organic sample. An advantage of this procedure is that the sample is exposed to relatively low temperatures only. Therefore no volatilization losses are found except for very volatile elements. Kaiser (7) found that several organic samples could be destructed in a short time but the destruction of a dried blood sample required a period of about 8 h. Because of this we modified the procedure. The sample is brought into contact with the plasma. However, in this way the sample is exposed to a much higher temperature and volatilization of less volatile elements may occur. T o overcome possible volatilization of Te or Sb, a watercooled cold finger is placed inside the ashing apparatus just above the plasma. Condensed T e or S b compounds are removed from the cold finger by reflux with the 0.1 M HC1 solution. In this way we reduced the ashing time needed for a dried blood sample to 20 min. (b) Reduction of Sb. After the ashing procedure, Sb is present in the pentavalent state. However, trivalent Sb is needed for the extraction-reextraction procedure. Because of this, all Sb has to be converted into the trivalent state. For this we modified the procedure described by Wyatt (9). The chemicals used for the reduction do not interfere with the extraction and the measurement of Sb. (c) Extraction-Reextraction. It was made clear by the experiments on interferences, described below, that separation of Sb or T e from the remaining blood salts after ashing a blood sample is necessary. Therefore an extraction-reextraction procedure was applied. By the extraction Sb and T e are separated from the blood salts and by the reextraction Sb and T e are transferred again into an acidified aqueous phase as required by the measurement. The extraction of Sb and Te present in diluted HCI was reported by Bode (6). We found that Te and Sb could be reextracted into an acidified aqueous phase by Cu2+in 0.1 M HC1. We added Cu2+as it is known

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Table IT. Te (258.6 nm) Signals Found after Direct Measurement and after the Extraction-Reextraction Procedure (Excitation Buffer 50 p g of KI, 100 p L of Reextract Introduced into the EDL) signals obtained Te concn signals after ( r e ) in obtained extraction original after (re)- from (diluted) blood salt soh direct extraction in (ngiml) measlirement pure salt soln matrix 10

5 2 1 0.2 0.05

0.01

4 0 0 ; 4CO; 412 400; 4 0 6 ; 4 4 0 388; 400; 3 6 5 4 3 5 ; 348 210;284 132;105 62; 51 30; 2 1 6;8;3 5 6 h ; ’ib

4 3 7 ; 213; 330 11.8; 1 4 1 ; 206 1 9 7 ; 4 5 9 ; 437 1 1 7 ; 1 3 6 ; 1 3 0 249 117;159 96; 109 41 ; 39; 61 3 2 ; 66; 51 24; 24 9; 1 2 4a;6

1 3 ; 11

500 g L instead of 1 0 0 p L reAfter 312 enrichment. extract was introduced into the EDL.

__---

Table 111. Recoveries of the Extraction-Reextraction Procedure of Te Measured with the KI Excitation Buffer Recovery, % pure salt blood salt Te concn., matrix ng1mL solution 78 42 41 43 44

10 5 2 1 0.2

39

48

to give very stable complexes with DaDTC. Furthermore we found no interference of Cu2+with the measurement. The mechanism of the extraction-reextraction procedure is supposed to be: for Te:

TeCldA1+ 4 DaDTCo

+ 2 Cu2+A2

Te(DTCIdo + 4 DaCl,,

(1)

+ 2 Cu(DTC),o

(2)

SKISA1 + 3 DaDTCo e Sb(DTC),o + 3 DaCIA,

(3)

Te(DTC),o

Te4+**

and for Sb:

2 Sb(DTC),o

+ 3 Cu2+A2

2 Sb3+A2+ 3 Cu(DTC),o (4)

(0 = organic phase, A1 = original aqueous phase, A2 = final aqueous phase, Da = diethylammonium, DTC = diethyldithiocarbamate). It may be expected that high concentrations of Cu2+and DaDTC improve the recovery. However, too high a concentration of these compounds (or of the decomposition products of the rather unstable DaDTC) present in the final aqueous phase will interfere with the measurement of Sb and T e seriously (see “Interferences”). Because of this the concentration of either Cu2+ or DaDTC to be applied is limited. Both for measurement of Sb and T e with Bi1,-CsI or with KI as an excitation buffer, a decrease of the Sb or Te recovery is found on performing the extraction-reextraction procedure from a solution containing the inorganic blood salts. The concentration of the inorganic blood salts varied between 10 and 50% of the concentration of inorganic salts in (undiluted) human blood.

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ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979

Table IV. Recoveries of the Reduction Extraction-Reextraction Procedures of Sb from the Blood Salt Matrix pg per EDL recovery and no. of of the total measurements average net 0 signal signal procedure, % 0( 4 ~ )

15

80 (4X )

38

160 ( 4 X ) 320 (5X ) 625 (6X )

51 104 171

0 23 36

43

89

34 39

156

40

Some experimental results obtained on using the KI excitation buffer are given in Table 11; the corresponding recoveries are given in Table 111. From these the following conclusions can be drawn: (i) A nonlinear calibration curve is found on using the KI excitation buffer. (ii) The pooled value for the RSD calculated from all direct measurements is 17% (23 DF); this value is 30% (16 DF) if extraction is included. (iii) In the concentration range of interest (between 0.2 and 5 ng/mL final solution), extraction recovery is about 45%. The recovery is not significantly influenced in the applied concentration range by the presence of blood salts. Some experiments of T e have been performed with a Bi13-CsI excitation buffer ( 4 ) . Between 0.16 and 1.6 ng/mL of Te, we found recoveries of about 90% in the absence of blood salts; addition of blood salts diminished the recoveries to about 57%. Surprisingly the recovery of the extractionreextraction procedure seems to be influenced by the type of the excitation buffer used. This may be explained by the assumption that the measurement by the EDL method is more seriously affected by contaminations from the extractionreextraction procedure on use of the KI excitation buffer than on use of the Bi13-CsI buffer. The recovery of Sb was investigated for the combination of reduction-extraction-reextraction only. The Bi13-CsI excitation buffer was used in the experiments. In the absence of blood salts, 100% recovery was found. However, for amounts of S b between 80 and 625 pg (1.28 and 10 ng/mL) the recoveries were only 40% if the blood salt matrix was used. See Table IV. (d) Measurements and Interferences. In earlier work KI was used as an excitation buffer ( 3 , 4 ) but in later work we found the combination of Bi13 and CsI to be a more favorable excitation buffer. The main disadvantage of the KI buffer is the serious dependency on time of the analyte signal as well as of the background signal. Because of this the accuracy of the method is poor on use of KI. Both analyte and background signal were found to be more stable on use of the Bi1,-CsI buffer, resulting in an improved accuracy. However, the detection limits may be slightly inferior for some metals if the Bi13-CsI buffer is applied. In the interference experiments we found with all analyte elements a significant decrease of the analyte signal if 0.5-5 pg of alkaline earths and alkali metals, 1 pug of foreign anions (e.g. P043-,NO,-, or S042-), 0.2 pg of organic matter, about 10 ng of In, T1, Cr, or T e or a few pg of Cu, Zn, Hg, or P b are present in the EDL. These interferences are roughly independent of the type of excitation buffer used. (e) Radiochemical Experiments. The radiochemical experiments were used as a control on the spectrochemical experiments. Furthermore they gave information on some problems that could not be solved by spectrochemistry. In the experiments, denoted A to F under Experimental, exactly the same concentration of S b and the same procedure as in the normal extraction-reextraction procedure were used. The maximum number of counts min-' obtained for the reference r as well as the 100% recovery was about 3000. The

Table V . Radiochemically Determined Recoveries (%) of the Reduction (Re)extraction Procedure

Applied on 0 . 5 ng/mL Sb D: Red.and A: Red. and extr. from exfr. from B: Red. from C: Extr. from the blood pure salt the blood salts the blood salts salts matrix, solution, % matrix, % matrix, 70' % 112 76 95 88 105 88 103 89 101

89

95

90

~

_

_

Table VI. Te 238.6-nm Signals Found When Measuring Some Blood Samples. Excitation Buffer 50 pig of KI sample no. Te signal sample no. Te signal I

I+ 0.5

ng/mL Te IT 5 ng/mL Te I1 I1 + 0.5

ng/mL Te

11;

5

ng/mL Te

9; 6;4.5 19

7

I11 IV

120

v

7

V

4;

6.5

6; 7

+

0.5

14; 17

ng/mL Te 19

VI

5; 8

105

VI1

3; 8

normal background value was about 800 cpm. From the activities of Ft (indicating the fraction of Sb* not reextracted) and F , (the fraction of Sb* not extracted) no particular conclusions could be drawn, for these activities did not exceed the background value significantly. From the 7 activity of the reextraction phase ( x cpm) the recoveries listed in Table V could be determined. From Table V the following conclusions are drawn: (i) The recovery of the combined reduction extraction-reextraction steps a t the 0.5 ng/mL S b level is 100% for a solution of the pure Sb salts. (ii) If the solution also contained the (diluted) blood salts the recovery decreases to 85%. (iii) The decrease in the recovery is mainly due to interference by the blood salts on the reduction step. (iv) The recoveries found radiochemically are in good agreement with those found optically. The recoveries over 100% can be explained by an estimated total error in the procedure of about 10%. To check the ashing procedure, 2.5 ng of Sb* was added to 1.5 mL of human blood. This was dried, ashed, and refluxed in the usual way. The y activity ( y cpm) of 1 mL of the solution obtained is compared with the activity of 1 mL of the reference solution ( r cpm). From these figures the recovery of the destruction step is found as ( y - u ) / ( r - a ) x 100%. The average recovery found is 66% (3 measurements). However, 100% recovery for the destruction step was found on reflux with 0.1 M HF instead of HCl. From this the conclusion can be drawn that the destruction losses are not caused by volatilization of Sb during the destruction but that part of the Sb is fused into the quartz wall of the ashing tube. The overall recovery of the total procedure was also checked radiochemically using a blood sample. The overall recovery was found to be 40%. Based on the recoveries for the separate steps an overall recovery of 0.85 X 0.66 X 100% = 55% is to be expected. This leads to the conclusion that the reduction-extraction-reextraction procedure is more seriously interfered with by the compounds left from a real blood sample after destruction than by the synthetic blood salts. Blood Sample Measurements. The natural T e content in several 1.5-mL blood samples of healthy people was determined by the standard addition method. The results of these measurements are shown in Table VI. From this a value for T e of 0.2 to 0.3 ng/mL of blood can be calculated except

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ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979

Table VII. Sb 287.8-nm Signals Found for Various Amounts of Sb. Excitation Buffer 2 . 5 f i g Bi t 2.5 p g Cs as Iodides. Filler Gas H, -

Sb,Pg

signal I

0 40 80 160 310 625 1250

0; 0 31; 2 6 ; 34 5 2 ; 5 2 ; 54 1 2 1 ; 1 0 5 ; 115 227; 229; 225 393; 378; 413 803; 779; 826

I

-

I/pgSb 0

30 53 115 227 395 802

0.75 0.66 0.72 0.73 0.63 0.64

Table VIII. Natural Sb Contents of 34 Preselected Blood Samples frequency contents, ng/mL 0.0-0.5 0.6-1.0 1 .l-1.5

5x 9x 1lX

1.6-2.0

3x

2.1-2.5 2.9 5.3

4x 1x I X

for sample VII. For this sample 0.15 ng/mL is found. T o determine the natural Sb content of human blood, we pooled blood samples of healthy people to give a reference blood sample. This reference sample was divided into several 1.5-mL portions. The signal from the natural Sb content of human blood was measured for the reference sample. The same determinations were made with 1.5-mL portions of the reference blood sample spiked with 0.1, 1,and 5 ng/mL Sb, respectively. For the reextraction 5 mL of reextraction phase was used in all determinations giving a dilution in respect to the 1.5-mL blood sample of 5/1.5 times. T h e Sb content of the reference blood sample was determined in two ways: (1) By plotting graphically as usual with the standard addition method. (2) By calculation using the data given in Table VII, analog to the T e determination. By both methods a Sb content of 1 ng/mL for the reference blood sample was found. Finally the S b content of 34 selected blood samples (the P b content already determined by flameless AAS) was determined. The samples were taken from people that might have been exposed to high lead concentrations. The sample volumes available were varying from 0.5 to 1.3 mL, giving after

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reextraction with 5 mL of reextraction phase, dilution factors of 10.0 to 3.8. Before and after each three measurements a blank was run, meaning a complete experiment except for the dried blood in the asher. For each run of three determinations, the mean of the blanks measured just before and after the run were taken into account. The recovery was checked eight times, a t regular intervals, during the 34 analyses. This was done by standard addition to the reference blood sample of 1.0 ng Sb/mL. The mean value of these eight recovery experiments (40.5%; RSD = 15%) was taken into account for each of the blood samples. The RSD for the measurement of the 34 blood samples may be expected to be in the same order of magnitude as the RSD of the eight recovery experiments, i.e. 15%. Sample B24A, sample volume 1mL, is taken as an example for the concentration calculation. An S b signal of 22 scale divisions is found. The mean of the blanks measured before and after the sample run of 7 scale divisions gives a net signal for sample B24A of 22 - 7 = 15 scale divisions. This net signal corresponds with 20 pg of Sb (see Table VII) introduced with 100 pL of reextract phase into the EDL. With 40.5% overall recovery and a dilution factor of 5, the Sb content of blood sample B24A is 5 x 20 x 100/40.5 = 247 pg of Sb/100 pL or 2.5 ng of Sb/mL of blood. The results of the determinations are summarized in Table

VIII. ACKNOWLEDGMENT The authors thank R. F. M. Herber, Amsterdam, for supplying the blood samples for the determination of Sb and for the P b values of these samples.

LITERATURE CITED (1) Picogram analyse door spectrale emissie vanuit een gesloten atoomreservoir, A. van Sandwijk. Ph.D. Thesis, RijksuniversiteitUtrecht, April 1974. (2) A. van Sandwijk, P. F. E. van Montfort, and J. Agterdenbos, Talanta, 20, 495 (1973). (3) A. van Sandwijk and J. Agterdenbos, Talanta, 21, 360 (1974). (4) P. F. E. van Montfort and J. Agterdenbos, Talanla, 21, 660 (1974). (5) P. F. E. van Monttort, J. Agterdenbos, R . Denissen, M. Piet, and A. van Sandwijk, Spectrochim. Acta, Part B . , 33, 47 (1978). (6) H. Bode and F. Neumann, Fresenius' 2 . Anal. Chem., 169, 410 (1959). (7) G.Kaiser, P. Tschopel, and G. Tolg, Fresenius' Z. Anal. Chem., 253, 177 (1971). (8) B. A. H. G. Jiitte and J. Agterdenbos. Spectrochim. Acta, Part 8,in press. (9) P. F. Wyatt, Analyst (London), 80, 368 (1955).

RECEIVED for review January 29,1979. Accepted May 15,1979.

Elemental Concentrations in the United States Geological Survey's Geochemical Exploration Reference Samples -A Review Ernest S. Gladney," Daniel R. Perrin, James W. Owens, and Daryl Knab University of California, Los Alamos Scientific Laboratory P.O. Box 1663, Los Alamos, New Mexico 87545

Silicate standard reference materials have been largely depleted. The function and value of these materials and the adequacy of several certification processes is examined. Concentrations of 42 elements measured at this laboratory are presented along with the available comparative data.

Internationally recognized standard reference materials provide an invaluable means for comparing data among widely separated laboratories. Furthermore, they provide a method to compare the quality, accuracy. and precision of data derived from a variety of analytical techniques, all of which purport

0003-2700/79/0351-1557$01,00/0 0 1979 American Chemical Society