Environmental Air Analysis for Ultratrace Concentrations of Beryllium by Gas Chromatography William D. Ross Monsanto Research Corp., Dayton Laboratory, Dayton, Ohio 45407
Robert E. Severs' Aerospace Research Laboratories, ARL/LJ,Wright-Patterson Air Force Base, Ohio 45433
A routine method of analysis for ultratrace concentrations of beryllium in particulate matter collected on air filters and in water is described. The particulate matter o n the filters is ashed, the residue is digested with acid, and the resulting solution is buffered to the optimum pH for solvent extraction. Potential interfering metals are eliminated by masking with EDTA. A benzene solution of trifluoroacetylacetone [H(tfa)l is allowed t o react with the beryllium in the aqueous solution to form Be(tfa)?. The organic extract is injected into a gas chromatograph equipped with an electron-capture detector. The chromatographic peak resulting from Be(tfa)2 formed from the unknown solution is compared with standard Be(tfa)s solutions for quantitation. The results indicate that the gas chromatographic method is more sensitive and reproducible than any other method now being used for the determination of beryllium in environmental samples. Analysis of air filters showed beryllium concentrations from 0.00016 t o 0.00049 pg of Be/m3 of air in the 14 urban samples examined.
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nalytical methods that can readily detect ultratrace levels of beryllium in air are urgently needed because of its high toxicity. Better environmental surveillance techniques are essential because of the widening use of beryllium in industry and space activities---e.g., rocket fuels. The chelation-gas chromatographic method for determining this metal in various media-e.g., water, biological fluids, and lunar soil-is well suited for ultrasensitive monitoring for beryllium in the environment. Instrumentation is relatively inexpensive, and the technique is easy enough to be readily conducted by trained technicians. A general review of metal analysis by gas chromatography can be found in a book by Moshier and Sievers (1965). The gas chromatographic (gc) analytical method for determination of beryllium was first described in 1966 when lower limits of detection were found to be about 4 X g [recently improved to about 4 X lo-" g (Sievers et al., 1971)] where quantitative formation and extraction of Be from water by solvent extraction of the metal via chelation with trifluoroacetylacetone [H(tfa)l have been achieved (Ross and Sievers, 1968). Noweir and Cholak (1969) determined beryllium in biological tissues and in air by a similar method, and Taylor et al. (1968) have demonstrated that Be in small amounts of biological materials can be reacted directly with H(tfa) in glass capsules and determined quantitatively by gas chromaTo whom correspondence should be addressed.
tography. The gc-chelation method has recently been used in the analysis of lunar soils, meteorites, and terrestrial samples for the quantitative determination of beryllium at sub-ppm levels (Sievers et al., 1971). The objective of the present investigation was t o develop a rapid, ultrasensitive, and reliable analytical method for the analysis of beryllium in airborne suspended particulate matter collected on glass filters. The gc method described in this paper has enough sensitivity to detect beryllium in all filter digests analyzed with sensitivity to spare. By the emission spectrographic method now used at Air Pollution Control Otfice, beryllium was detected in less than 15 % of the samples examined. Experirwn tal Reagents. 0.164M H(tfa) I N NANOGRADEBENZENE (MALLINCKRODT). This solution was made by diluting 2 ml of freshly distilled H(tfa) (Pierce Chemical Co.) in 100 ml of benzene. The solution was stored in a silanized, 100-ml borosilicate glass volumetric flask. Benzene solutions of H(tfa) and also neat H(tfa) are subject to slow decomposition o n standing which produces spurious gc peaks. 3N NaOH SOLUTIONFOR NEUTRALIZING REAGENTA N D 0.1N NaOH BACKWASHING REAGENT. These solutions were prepared from Matheson, Coleman and Bell (MCB)analyzed RG NaOH and deionized water. ETHYLENEDIAMINETETRAACETIC ACID (EDTA)-BUFFER SOLUTION. This solution was prepared by weighing out 5.15 g of Na?EDrA.H-O (G. F. Smith Chemical Co.), 85 g of NaOAc. 3 H 2 0 (MCB,reagent), and 6.25 ml of glacial acetic acid (Baker, Ultrex) and dissolving these reagents in 500 ml of deionized water. Standard Beryllium Solutions. Standard Be(tfa)L solutions were prepared by dissolving Be(tfa)i, purified by sublimation, in Nanograde (Mallinckrodt) benzene. Further dilutions were made until the resulting concentration was 1.0 X 10-l' g of Be/pl. This solution was prepared every two weeks. The standard aqueous beryllium solutions were prepared by dissolving a beryllium metal chip in concentrated HC1 (Du Pont, reagent) and diluting with deionized water t o a n ultimate concentration of 9.2 X 10-l2 g of Be(II)/pl. Silariization of Glassware. The standard samples, Be(tfa)2 and aqueous Be(II), were stored in borosilicate glass volumetric flasks which had been cleaned in Chromerge cleaning solution and then silanized to reduce any reactive sites. This was achieved by filling the flasks with a 20% solution of hexamethyldisilazane (HMDS)in benzene and letting them stand overnight. The reaction vessels (5-ml culture tubey) were treated by a similar method. Preparation of Filter Digests. The air filter sample digests Volume 6, Number 2, February 1972
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used in this investigation were obtained from the Division of Air Quality and Emission Data of the National Air Pollution Office (APCO). Samples were obtained by drawing known volumes of air through porous filters from various cities in the United States. Glass-fiber filters which retain particles as small as 0.3 p were used in conjunction with high volume samplers. Filter size was 7 X 9 in. of exposed surface. The filter permitted passage of between 50 and 60 f t a of air/min. The filters analyzed had a total of 2200 m 3 of air passed through them over a 24-hr period. One-inch strips were cut from these filters and were digested by the following procedure described by Thompson et al. (1970). The digestion portion of the method has been used by APCO routinely as the standard pretreatment procedure for metal analysis by emission spectrography. The strips were placed in borosilicate glass boats and placed in a Tracerlabs low-temperature asher at about 150°C for 1 hr at 1 mm chamber pressure with a n oxygen flow of 50 cc/min. The ashed filter was placed in a glass thimble, and the thimble was placed in a n extraction tube. A 125-ml Erlenmeyer flask was charged with 8 ml of constant boiling HCI (19%, D u Pont reagent grade) and 32 ml of H N O d (40%;, Baker and Adams, redistilled ACS grade). The flask was attached to the extraction tube and the extraction tube was fitted with an Ahlin condenser. The acid was refluxed over the sample for 3 hr. The extraction tube and the condenser were removed, and the flask was fitted with a thermometer adapter. The extracted liquid was concentrated to 1-2 ml on a hot plate, cooled, and allowed to stand overnight. This material was quantitatively transferred to a graduated 15-ml centrifuge tube with three washings of 5 to 10 drops of diluted acid. The samples were diluted to 4.4 ml with distilled water. The tubes were then centrifuged at 2000 rpm for 30 min, and the supernatant was transferred to polypropylene tubes ready for analysis. Procedure for Gas Chromatographic Analysis. One milliliter of the aqua regia filter digest was accurately pipetted into a 5-ml borosilicate glass culture tube fitted with a screw cap. One milliliter of EDTA-Sodium acetate buffer solution was added to the culture tube. Adequate amounts of a 3 N NaOH solution were added to bring the p H to between 5.5 and 6.0. The requirement was between 0.8 and 1.3 ml, depending o n the original p H of the digest. The tube containing a small Teflon-coated magnetic stirrer was capped and inserted into a n oil bath maintained at 93°C on a Corning stirring hot plate. The sample was heated and stirred vigorously for 10 min. The tube was cooled, and 1 ml of 0.164M H(tfa) in benzene was added. The tube was capped and placed above the stirring mechanism of the hot plate and stirred for another 15 min a t ambient temperatures. The tube was permitted to stand until organic and aqueous layers were separated. The organic layer was transferred with a medicine dropper t o a 2-dram vial and 2 ml of 0.1N NaOH was added. This mixture was quickly shaken by hand for 5 sec to remove excess H(tfa) from the organic layer. The two phases were immediately separated by withdrawing the organic layer with a medicine dropper and transferring it to another 2-dram vial which was then capped. This step must be performed rapidly and reproducibly because intolerably large amounts of Be will otherwise be lost and both precision and accuracy will suffer. Five 1-pl aliquots of organic layer were repetitively in156 Environmental Science & Technology
jected into the gas chromatograph. The mean of peak heights from the Be(tfa)a peaks in the unknown solutions were compared with the average from five analyses of a standard solution of Be(tfa)a. Over the concentration range studied the response is essentially linear so quantitation is simplified and peak height ratios can be used for the calculation of Be found. Instrument Conditions. Gas chromatograph: Hewlett Packard Model 402 high efficiency gas chromatograph equipped with a 3H source electron-capture detector. Column: 2 m X 3 mm i.d. borosilicate glass column packed with 2 . 8 z W-98 silicone (Union Carbide) on Diataport S (Hewlett Packard). Carrier Gas: CH4, 10%; Ar, 90%; 54.5 ml/min. Column temp: 110°C. Detector temp: 200°C. On-column injection (no additional heat at site of injection). Analysis for Blank. Periodic investigations were made to determine whether any interfering peaks, resulting from impurities o r the reaction of reagents, coincided with the same retention time of Be(tfa)n. Exactly the same analytical procedure and reagents in the analysis of unknowns were used. Deionized water containing aqua regia reagent was used in lieu of the unknown filter digest. The data obtained for 1 pl of organic layer at an electrometer setting of range 10, attenuation 32, indicated peak heights of 5 mm which corresponds t o a blank of
