Environmental Analysis Problems Created by Unexpected Volatile Beryllium Compounds in Various Samples Marilyn S. Black and Robert E. Sievers' Aerospace Research Laboratories, Wright-Patterson Air Force Base, Ohio 45433
An increasing awareness of environmental pollution and the need for standard reference materials have prompted recent investigations into the occurrence of the toxic metal beryllium in various matrices and have necessitated development of analytical methods which will provide accurate and precise results. The gas chromatographic (GC) method for the detection of beryllium coupled with prior extraction of the metal uia chelation with trifluoroacetylacetone H(tfa) has proved to be very sensitive and precise in the measurement of ultratrace levels of beryllium (1-6). A recent study of beryllium present in Standard Reference Orchard Leaves (National Bureau of Standards) in which this technique was utilized has indicated the presence of volatile beryllium compounds. Because inprecise results were obtained when different methods of destroying the organic matrix were used, a detailed investigation of the parameters involved, including the destruction of the organic material, trapping of volatile vapors, and GC detection, was undertaken. Air particulate samples obtained by the Environmental Protection Agency (Office of Air Programs, Research Triangle, N.C.) at a beryllium machining facility were also analyzed for beryllium. The samples had been collected in a sampling train which consisted of an ordinary EPA sampling probe, two Millipore AA filters backed by Whatman filters in series, two water impingers in series, a dry impinger to catch water condensation, and a cold trap which was changed halfway through the sampling. In the first half of the sampling, the cold trap was an impinger filled with glass beads and, in the last half, an impinger containing hexane, both of which were immersed in a Dry Ice-acetone bath. The presence of beryllium in the impingers and the existence of higher beryllium concentrations in the cold traps than in the water impingers indicate that volatile beryllium compounds are being emitted in beryllium machining operations.
EXPERIMENTAL Reagents: All chemicals were reagent grade unless otherwise specified. Nitric and sulfuric acids were ultrapure quality (Ultrex, J . T . Baker) and all water used was distilled-demineralized. Glassware, prior to use, was silanized for a t least 24 hr with a 25% (v/v) solution of hexamethyldisilazane (Pierce Chemical Co.) in benzene. A 0.0824M solution of H(tfa) was made by diluting 1 ml of neat H(tfa) (Pierce Chemical Co.) to 100 ml with Nanograde benzene (Mallinckrodt Chemical Works). A 0.3M solution of Na2EDTA was prepared by dissolving 14 g of NazEDTA (G. Frederick Smith Chemical Co.) in 100 ml of H2O. A high capacity buffer with a pH 5.5, 2M NaOAc, and 0.34M HOAc was prepared by diluting 136 g of NaOAc.3HzO (Matheson Coleman and Bell) Author to whom reprint requests should be sent. ( 1 ) W. D. Ross and R. E. Sievers, "Gas Chromatography 1966," A. Littlewood. Ed., The Institute of Petroleum, London, 1967, p 272. (2) W. D. Ross and R. E. Sievers, Talanfa, 15,87 (1968). (3) M. L. Taylor. E. L. Arnold, and R . E. Sievers, Anal. Lett., 1, 735 (1968). (4) M. H . Noweir and J. Cholak, Environ. Sci. Techno/.,3,927 (1969). (5) W. D. Ross and R. E. Sievers, Environ. Sci. Technoi.. 6, 155 (1972). (6) K. J. Eisentraut, D. J. Griest, and R. E. Sievers, Anal. Chern.. 43, 2003 (1971).
and 10 ml of Ultrex glacial acetic acid to 500 ml with H2O. NaOH solutions, 12, 6, and 0.1M, were prepared by dissolving the appropriate amount of NaOH (Matheson Coleman and Bell) in HzO. A stock solution of Be(tfa)z, containing 1.07 X g/ml Be, was prepared by dissolving 3.734 mg of freshly sublimed Be(tfa)Z in 100 ml of benzene. Standard solutions used in the analyses were subsequently prepared from this stock solution just prior to chromatographic analysis. Digestion of Orchard Leaves. W e t Digestion in a n Open Container. Approximately 5 g of orchard leaves (freeze dried) was weighed into a 250-ml beaker. Subsequently, 35 ml of concentrated "03 and 15 ml of concentrated were added, and the solution was swirled and gently heated on a hot plate until foaming subsided. The solution was then heated to 180 "C and digested for 5 hr on the hot plate. Additional "03 (-20 ml) was periodically added until the organic material was completely dissolved. After completion of the digestion, the solution was cooled and quantitatively transferred to a 100-ml volumetric flask and diluted to the mark with HzO. W e t Digestion i n a Flask with a Reflux Condenser. Approximately 5 g of orchard leaves was weighed into a 250-ml digestion flask equipped with a standard 20/40 taper joint. After adding 35 and 15 ml of concentrated H&04, the ml of concentrated "03 solution was swirled and a 500-mm Graham condenser with circulating cold water was attached. The solution was first heated gently and then heated to 180 "C with a heating mantle. Periodically during the digestion, the condenser was rinsed with a few milliliters of "03. After 4 hr the digestion was complete and the heat was removed. The condenser was rinsed with "03 and H2O and the flask, after cooling, was removed. The solution was quantitatively transferred to a 100-ml volumetric flask and diluted with H2O. Low Temperature Ashing in a n Oxygen Plasma. Approximately 250 mg of orchard leaves was placed in a Pyrex sample boat and dispensed to form a very thin layer. The sample boat along with an empty boat (for the blank) were placed in the oxidizing chamber of a Tracerlab low temperature asher which reportedly reaches a maximum temperature of 150 "C. With a chamber pressure of 1 mm and an 0 2 flow of 60 ml/min, the ashing was complete within 12 hr. A Dry Ice trap was attached between the chamber and vacuum pump so that any volatiles released during ashing would be trapped. After the ashing was complete, the ash of the orchard leaves was dissolved in a few milliliters of 6N H N 0 3 and the solution was transferred to a 30-ml polyethylene bottle. Gas Chromatographic Procedure. GC Parameters. A Hewlett-Packard Model 5750 gas chromatograph equipped with a 3H source electron capture detector was used in the analyses. The column was 2-m X 3-mm i.d. borosilicate glass packed with 3.8% W-98 silicone (Union Carbide) on Diataport S, 80/100 mesh (Hewlett-Packard). The flow rate of the carrier gas, 10% CHI/ 90% Ar, was 52 ml/min. Instrument conditions were: column temperature, 105 "C; detector temperature, 170 "C; and injection port temperature, 180 "C. On-column injection was used. Sample Analysis. Ten milliliters of the acid digest of the orchard leaves was transferred to a 50-ml polyethylene bottle and the pH was adjusted to 5 with 12 and 6M NaOH. Two milliliters of the EDTA solution and 2.5 ml of buffer solution were added to the bottle which was then shaken for 10 min on a mechanical shaker and heated for 10 min in a 95 "C water bath. After cooling, 10 ml of the 0.0824M H(tfa) was added and the mixture mechanically shaken for 15 min. The solution was then transferred to a separatory funnel and the aqueous layer drained off. The remaining organic layer was quickly hand shaken for 5 sec with 10 ml of 0.1M NaOH to remove excess H(tfa). The two phases were immediately separated. Five 1 - ~ aliquots 1 of the organic layer 'were injected into the GC for analysis. The mean of the peak heights was compared with those of standard solutions of various concentra-
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Table I. Beryllium Concentration in Orchard Leaves as a Function of Organic Digestion Procedures Type of digestion Wet digestion, HN03/H2S04 Open beaker Covered beaker Low temperature asher (ash), 02 plasma Low temperature asher (cold trap)= Wet digestion, HN03/H2S04 with condenser a
Ppm Be (with re1 std dev)
0.017 f 0.003 0.017 f 0.002 0.0075f 0.0036
0.085 0.11
f 0.01
Average of two measurements.
Table 11. Beryllium Concentrations of lmpinger Samples Sample Be content, pg First water impinger 0.016 Second water impinger 0.012 Glass bead cold trapa 0.025 Hexane cold trap* 0.085 Connected to the second water impinger during the first half of the sampling period. * Connected to the second water impinger during the second half of the sampling period.
Table I I I. Comparison of Electron Capture Gas Chromatographic (GC) and Gas ChromatographicMass Spectrometric (GC-MS) Quantitative Analysis Sample Acid digest of orchard leaves LTA cold trap lmpinger hexane cold trap
5.2 X 10-l2 7.2 X lo-" 8.5X lo-"
5.6 X 10-l2 7.7X 10-l2 8.9 X
tions of Be(tfa),. Previous studies have shown that peak height measurements give an accurate and precise representation of the beryllium content (6). Calibration curves and results were calculated using a Hewlett-Packard 9100 A calculator/9125 plotter system. The ashed digest was treated in an identical manner. Since only a 250-mg sample was ashed, the entire solution was used in the analysis. The volatiles trapped in the cold trap during low temperature ashing were analyzed in a similar manner. The trap was rinsed with approximately 10 ml of 6N "03 into a 50-ml polyethylene bottle, and the solution was subsequently treated as previously discussed. The four EPA samples were sent to this lab in their sealed original impingers. Two were water impingers and the other two were filled with hexane and glass beads, respectively, both of which had been immersed in a Dry Ice-acetone bath. Ten-milliliter aliquots of the solutions were taken for analysis and chemically treated as the digest aliquots previously discussed. The glass beads were first leached with a small volume of 6N "03 and water in order to dissolve any condensed or adsorbed beryllium compounds. Independent tests have shown that beryllium blanks are insignificant when clean glass surfaces are leached similarly.
RESULTS AND DISCUSSION The beryllium concentrations of the orchard leaves determined following different types of organic digestion procedures are given in Table I. For each digestion procedure three to six samples were treated and five aliquots of each were analyzed so that 15 to 30 data points were available for the statistical analysis. As can be seen there was an 85% loss of beryllium when the digestion was carried out in an open beaker in comparison with the digestion carried out under closed conditions with a condenser. The addition of a cover glass to the beaker did not appreciably reduce the amount of beryllium lost. The loss of beryllium using the low temperature asher was even greater than that obtained with the open beaker digestion, viz., a 93% loss of the beryllium present. The volatile condensate caught in the cold trap leading from the asher 1774
chamber to the vacuum pump during low temperature ashing was also analyzed to determine whether beryllium was present. The trap was rinsed with 6N " 0 3 and this solution was analyzed after neutralizing and treating with H(tfa); a peak arising from Be(tfa)z was observed in the sample chromatogram. This indicated that a volatile beryllium compound had been lost in the vapor phase during low temperature ashing. The amount of beryllium found is given in Table I. Blank samples were also analyzed, and the peak with the retention time of Be(tfa)z did not appear. The results of beryllium analyses of the impinger samples are given in Table 11. The beryllium content was found to be much higher in the cold traps than in the water impingers in spite of the fact that the cold traps came last in the flow train. The total collected beryllium in the cold traps was approximately four times the total in the water impingers. These data indicate the strong possibility of the existence of volatile beryllium compounds in the air in the beryllium machining facility. It has previously been assumed that beryllium only appears in suspended particulate matter. The volatile beryllium compounds apparently passed through the filters of the sampling train, were partially trapped in the water impingers, but were mostly condensed in the cold traps. The identity of the Be(tfa)z peak eluting from the gas chromatograph was confirmed using a sensitive gas chromatographic-mass spectrographic (GC-MS) system that is capable of detecting certain compounds eluting from the column at ultratrace levels. A Du Pont 21-491 double focusing mass spectrometer coupled to a Loenco Model 160 gas chromatograph was used (7). Sensitive mass peaks characteristic of Be(tfa)z, in this case 315 and 246, were monitored individually as the GC peak of interest eluted from the column. The mass scale was calibrated using a solid sample of beryllium trifluoroacetylacetonate which was introduced via a direct probe inlet. Various treated samples of the orchard leaves, the low temperature asher (LTA) residue, volatiles of LTA cold trap, and the impinger samples were analyzed using GC-MS and the identity of Be(fta)z was confirmed. Some quantitative measurements for beryllium were made by GC-MS and the results agreed well with those of the electron capture GC method, as shown in Table In. Calibration curves were obtained by injecting benzene solutions into the GC and, after pumping away the solvent, allowing the effluent to enter the mass spectrometer ion source. The mass peak was recorded as a function of time and peak areas were used for quantitative measurements. Extensive mass spectrometric experiments were performed to attempt to identify the naturally occurring volatile beryllium compound(s). After several months, however, these attempts were abandoned owing to the extraordinary difficulties encountered in trying to work with picogram quantities in the presence of very complex mixtures of other substances. CONCLUSIONS The results of this study indicate the existence of naturally occurring volatile beryllium compounds. The various digestion and ashing procedures of orchard leaves have shown that beryllium is lost in the vapor phase at relatively low temperatures (less than 200 "C). This suggests that a considerable amount (at least 90%) of the beryllium in the orchard leaves may be organically bound and that it is lost upon destruction of the organic matrix unless precautions are taken. It is therefore necessary for one ( 7 ) W . R. Wolf, M . L. Taylor, B. M . Hughes, T. 0. Tiernan, and R. E. Sievers,AnaL Chem., 44, 616 (1972).
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to consider Be loss in the vapor phase when pretreating for The impinger analyses are quite important from an industrial hygiene standpoint since beryllium was found in all the samples past the Millipore filters and appeared to be concentrated in the traps. This the contention that do exist and that they are present in the vapor state in facilities where beryllium is machined. These findings are environmentally significant since such volatile beryllium compounds may conceivably pose a previously unrecognized threat.
ACKNOWLEDGMENT We wish to thank Noel deNevers of the Environmental protectionAgency, Office of ~i~ programs,for providing impinger and cold trap samples and his helpful suggestions. The valuable assistance of Michael Taylor and Mason Hughes of the Aerospace Research Laboratories in spectrometric analyses is very much appreciatthe VU.
Received for review October 11, 1972. Accepted March 28, 1973.
Determination of Degree of Substitution in Sodium Carboxymethylcellulose by a Reverse Dye Partition Technique Sailes Mukhopadhyay,’ Bhairab Ch. Mitra,2 and Santi R. Palit Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-32, India
Various analytical procedures (1-3) for the determination of carboxylate groups present in carboxymethylcellulose (CMC) and its sodium salt have been proposed from time to time to determine the degree of substitution (DS), i. e . , the average number of sodium carboxymethyl groups substituted per anhydroglucose unit. A reverse dye partition (RDP) technique (4, 5 ) is described in this note as an alternative method for the determination of DS.
EXPERIMENTAL Reagents. Disulfine blue VN 150 (I.C.I.) was recrystallized from a mixture of methanol and acetone. n-Dodecylamine hydrochloride was prepared by passing dry hydrogen chloride gas through an alcoholic solution of n-dodecylamine. The hydrochloride was recrystallized from carbon tetrachloride using diethyl ether as the precipitant. Procedure. Four representative samples of Na-CMC with different degrees of substitution were prepared by the treatment of chloroacetic acid on cellulose. The resulting substituted cellulose samples were rigorously purified by repeated washing with 80 and 95% ethanol alternately and then drying the samples a t 50 “C. Aqueous solutions having concentrations in the range of 1.0 to 2.5 X g/l. were prepared with these samples. The pH’s of all the solutions were brought to exactly 6 . 5 by titration with the help of a pH meter. The matching of the pH of the control and the sample before partition is very critical. Buffering should be avoided. R D P Technique. A “dye reagent” was prepared by equilibrating an equal volume of a 0.005% w/v chloroform solution of ndodecylamine hydrochloride and a 0.01% w/v solution of disulfine blue VN 150 in 0.005N HC1. After partition, the deep blue colored chloroform layer was separated by centrifugation and stocked as “dye reagent.” Exactly equal volumes ( 5 ml) of the “dye reagent” and the aqueous solution of Na-CMC were shaken in a centrifuge tube. Present address, St. Stephen’s College, Delhi-7, India. Present address, Shri Ram Institute for Industrial Research, Delhi, India. R. S. Eyler, E. D. Klug, and F. Diephuis, Anal. Chem., 19, 24 (1947). K . Wilson,Sv. Papperstidn., 59, 218 (1956). A. Z. Conner and R. W. Eyler, Ana/. Chern.. 22, 1129 (1950). S. Mukhopadhyay. 6. C. Mitra, and S. R. Palit, Makromol. Chern., 141, 55 (1971). (5) D. K. Vidyarthi, S. Mukhopadhyay,and S. R. Palit, Makromol. Chern., 148, 1 (1971).
Table I . Determination of DS from RDPT Equiv
of carboxyl Concn of Corresponding per g ( A ) Na-CMC Diff in concn of of Na-CMC, Sample solution, absorbance Na-laurate, (l;)(i;l) no. g/l. X lo2 at 630 nm moi/l. X l o 5 (1)
( 1 1)
1 2 3 4
1.50 2.09 1.15 2.12
(111)
0.700 0.731 0.358 0.547
DS
(IV)
3.10 3.25 1.60 2.40
2.07 1.56 1.39 1.13
0.38 0.28 0.25 0.20
Some dye was transferred to the aqueous layer, leaving behind a less intense blue colored chloroform layer. After complete partition, the tubes were centrifuged and the absorbance of the chloroform layer was measured a t 630 nm. A “blank” test was done by shaking an equal volume of “dye reagent” and distilled water (pH 6 . 5 ) in a centrifuge tube, and the absorbance of the chloroform layer was measured. The difference in absorbance of the test and blank solutions was determined and compared with a calibration curve to find out the concentration of COO- ions (mol/l.) in the respective solutions. The calibration curve was obtained by plotting the difference in absorbance between blank and test us. different concentrations of sodium laurate ( 4 , 5 ) . Calculation.
DS = 162A/1 - 58A
(1)
where A is the equivalents of total carboxyl per gram of the sample.
RESULTS AND DISCUSSION The disulfine blue, which carries a SO3- group, forms a n ionic complex with the n-dodecylammonium chloride. The complex is soluble in the organic layer. When the blue complex is shaken with water, it dissociates to liberate the free dye which passes into the aqueous layer. This dissociation is enhanced with the presence of any polymer bearing negatively charged groups in the aqueous layer. The opposite effect is observed in the presence of -NH3+ groups. Other groups such as -OH, -SH, >C=O, or -CONH2 have no effect on the dye partition.
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