1485
Anal, Chem. 1985, 57. 1485-1488
0
2 and 3 of Figure 1, (3) flow rate of NaBH4 solution (line 6, Figure 1)and 1, 10-phenanthroline (line 5 ) , and (4) temperature of the quartz tube. Control of these conditions need not be critical. On the other hand, the absorbance varies considerably with the following factors: (1)flow rate of the argon carrier gas, (2) length of the quartz tube atomizer, and (3) diameter of the solution transmission tubings. Strict regulation of the carrier gas flow is thus required. The longer the quartz tube, the more absorbance is favored. Sixteen Centimeters is an accommodable length that would provide maximum absorption. All the solution lines are 0.56 mm i.d. Teflon tubings designed to minimize the flow volume (dead volume). Teflon tubing with larger diameter (1.35 mm i.d.) is used in two places, Le., the sample loop and the section of the reacting stream (FG in Figure 1). They are 140 and 25 cm long, respectively. Unlike method 1,there is no need to use mixing coils at the reacting-stream section (EF and FG in Figure 1);in fact, the shorter the path length in section FG, the less the effect of interferences. This is probably because the reaction time has been shortened, so that the interaction between Se and the interferents becomes less complete, while the fast reaction between Se and NaBH4 is unhindered. Although the concentration of HCl in the sample solution does not affect the signal response, an acidity lower than 30% HC1 results in increase of susceptibility of Cu interference. The blank value, however low, is mainly contributed by nitric acid and is not by hydrofluoric and perchloric acids. In order to maintain a minimum blank value, a good grade of nitric acid, such as the "Baker Analyzed" reagent, should be used. A batch of 50 samples can be digested simultaneously on a large hot plate. Complete digestion normally takes an hour. A total of 50-80 solution samples can be analyzed per hour.
5 2
1
I
I I
3
Sampling volume (ml)
I
1
0
15 30 Sampling time (sec.)
45
Flgure 2. Effect of sampling volume on sensitivity (4 ppb Se standard).
calculated. The results are shown in Table I together with the literature values. The precision of the method is expressed with an average relative standard deviation of 2.85%. The accuracy was demonstrated by the close agreement of the results with the literature values specifically by the result of 10.6 ppm on NBS 1633a (coal fly ash sample) certified at 10.3 f 0.6 ppm. For the USGS and CCRMP samples, the results agree well. For ANRT samples, the results on AN-G and BE-N are low compared with literature values. Once again the value of MA-N was found to be very low (10 ppb) contrary to the value (16.4 ppm) reported (11). The data in Imai's report ( 4 ) for NIM-G, -L, -N, and -P, which have low Se concentrations, are not appropriate since greater sensitivity is required than was quoted. At present, no data are available for the CRPG samples besides our sources. Because the sensitivity of the method has been drastically increased, improvement in accuracy is noticed when compared with the results from method 1. Samples with low Se concentration such as SDC-1, SY-2, MA-N, or NIM-N, which are unable to be determined by method 1, can now be determined with confidence. Furthermore, the method is less prone to chemical interferences. Samples with unusual matrices, such as GXRB (composite soil), can be determined with greater accuracy. Even a sample with very high As content, such as GXR-3 (4200 ppm As), can also be determined with the aid of standard addition technique. General Remarks. The absorbance does not vary appreciably with (1)concentration and type of acid in the sample solution, (2) concentration of the HCl carrier solution in lines
ACKNOWLEDGMENT
I thank Chris Riddle for reviewing the manuscript. Registry No. Se, 7782-49-2.
LITERATURE CITED (1) Chan, C. Y.; Balg, M. W. A. Anal. Lett. 1984, 17, 143-155. (2) Ruzicka, J.; Hansen, E. H. I n "Flow Injection Analysis"; Wiley Interscience: New York, 1981. ( 3 ) Astrom, 0. Anal. Chem. 1982, 5 4 , 190-193. (4) Imai, N.; Terashlma, S.; Ando, A. Geostand. Newsl. 1984, 8, 39-41. (5) Gladney, E. S.; Goode, W. E. Geostand. Newsl 1981, 5 , 31-64. (6) Gladney, E. S.; Burns, C. E. Geostand. Newsl. 1984, 8 , 119-154. (7) Abbey, S.CANMET Report No. 79-35, 1979, p 41. (8) Lavrakas, V.; Golembeskl, T. J.; Pappas, G.: Gregory, J. E. Anal. Chem. 1974, 46, 952-954. (9) Schnepfe, M. M. J. Res. U . S . Geol. Surv. 1974, 2 , 631-636. (10) Gladney, E. S.; Knab, D. Geostand. Newsl. 1981, 5 , 67-69. (11) Govlndaraju, K. Geostand. News/. 1980, 4 , 49-138. (12) Govlndaraju, K. Geostand. Newsl. 1982, 6 , 265.
RECEIVED for review November 19,1984. Accepted February 1,1985. This paper is published by permission of the Director, Ontario Geological Survey.
Detection of Amphetamine in Air by Solid Adsorbent Preconcentration and Gas Chromatographic Analysis A. H. Lawrence* and Lorne Elias Unsteady Aerodynamics Laboratory, National Aeronautical Establishment, National Research Council of Canada, Ottawa, Ontario K I A OR6,Canada A number of analytical methods are available for the identification and determination of amphetamine in various matrices. Recently, Lawrence and Macneil (I) reported a
method for the identification of amphetamine in street drug preparations by second-derivative ultraviolet spectrometry. Numerous papers have been published describing gas chro-
0003-2700/85/0357-1485$01.50/00 1985 American Chemical Society
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+,
ANALYTICAL CHEMISTRY, VOL. 57, NO. 7, JUNE 1985 (0)
S l L A N l Z E O G L A S S WOOL P L U G S
-AIR
AIR OUT-
TENAX
Table I. Experimental Data for the Field Sampling Test"
IN
- GC
(30me)
(b)
-AIR
/
TENAX-GC
init flow, L/min
final flow, L/min
(-5,O) (+5,0) (+5A (+5,2)
0.6 1.0 0.8
0.6
(+10,0)
0.9
1.0
1.0 0.8 1.0 0.9
"Temperature, 25 "C; relative humidity, 40%; wind velocity, 2 m/s.
S l L A N l Z E O G L A S S WOOL P L U G S
AIR OUT-
sampler no.
IN
AS CARITE OR SODA L I M E
(50mg)
(30mg)
Flgure 1. Adsorber sampling tubes for collection of amphetamine.
matographic (GC) methods for the determination of amphetamine and other phenylisopropylamine derivatives in blood, urine, and other biological extracts (2). Baker (3) reported the use of a GC system equipped with dual-flame-ionization (FID) and nitrogen-phosphorus (NPD) detectors for the identification of amphetamine, methamphetamine, and other illicit drugs in the liquid phase. However, the chemical literature lacks information on the specific detection of amphetamine vapor in air, although the sampling of other amines in air by means of absorption in acidic solution and subsequent GC analysis has been reported ( 4 , 5 ) . Another methodology, based on the use of adsorption tubes, has also been reported for the other amines: once the air sampling has been completed, the collected amines are quantitatively released either by leaching with a suitable solvent (6, 7) or by thermal desorption (8-10) and analyzed by GC. Analysis by thermal desorption directly into the GC is not only much faster than that obtained through solvent extraction but also allows the detection of much lower concentrations. We have previously investigated the capacity of a Tenax-GC adsorber tube to collect vapors of amphetamine from a trace vapor generator and have reported the determination of the vapor pressure of the amine (11). While the Tenax adsorbent was suitable for collecting amphetamine vapor from a purified air stream, it was found not to be suitable for use in ambient air sampling. The present paper describes a modification to the Tenax adsorber which renders the sampling methodology efficacious for amphetamine in the real-air scenario. EXPERIMENTAL SECTION Chemicals. D-Amphetamine sulfate (BDH lot 30603-35403) was obtained from Health and Welfare Canada. The free base was extracted from the sulfate salt following the procedure described by Predmore (12). Tenax-GC (35-60 mesh) was obtained from Supelco Inc. (Bellefonte, PA), Ultra Bond PEGS (80-100 mesh) from Alltech Assoc. (Deerfield,IL), Ascarite (20-30 mesh) from Arthur H. Thomas Co. (Philadelphia, PA), and sodium calcium hydrate (soda lime) (4 mesh) from Anachemia Chemicals Ltd. (Toronto, Ontario). Calibration solutions of amphetamine were prepared in Distilled-in-Glass grade n-hexane (Caledon, Georgetown, Ontario). Adsorption Tubes. The adsorption tubes used in this study were constructed of glass tubing, 7.5 cm long X 6.3 mm 0.d. X 4 mm i.d. with a small restriction in the middle, and contained a small amount of sorbent material held in place with plugs of silanized glass wool (13). Two types of tubes were used. The type shown in Figure l a contained about 30 mg of Tenax-GC while that depicted in Figure l b contained about 50 mg of Ascarite or soda lime placed just ahead of the Tenax packing. The tubes were conditioned overnight at 250 OC in a helium stream at a flow rate
of 50 mL/min. The tubes were capped and sealed in opaque bottles until use. Apparatus. A dynamic gas blending system was used to generate controlled levels of amphetamine vapor in (purified) air for test purposes. After sampling of the spiked air stream, adsorbers were interfaced to a specially modified GC for injection by thermal desorption. The GC was equipped with a nitrogenphosphorus detector (NPD), a six-port switching valve, and a two-stage desorption system. Operation of the GC and trace vapor source has been described elsewhere (11). Test Procedure. Laboratory experiments were conducted to compare the collection efficiency and the recovery of amphetamine from the two-component adsorbent system with that of the previously investigated Tenax system (11j. Air sampling was performed so that a continuous stream of laboratory compressed air containing a constant concentration of amphetamine entered the soda lime end of the tube (Figure lb). The carrier flow and the diluting flow were maintained at 2.1 mL/min and 15.7 L/min, respectively. The sampling time was 60 s, and the sampling flow rate was varied over 0.2-1.0 L/min to collect various amounts of amphetamine on the traps. After sampling, the adsorption tube was connected to the gas chromatograph for analysis, the Tenax end facing the switching valve. The recorded amphetamine peak area was compared with that of an amphetamine standard solution deposited with a syringe directly on the soda lime end of the adsorbent and analyzed in the same manner as an air sample. The concentration of the standard solution was 6 X g/pL. The recovery of amphetamine from the two-component adsorbent system was examined by depositing known amounts of amphetamine ca. 48 ng in n-hexane on the soda lime and analyzing the desorbate by GC as before. The recorded amphetamine peak area was compared with that of a similar quantity of solution deposited in an adsorption tube containing a plug of glass wool only. Field Sampling. A small-scale test grid was set up outdoors in which the trace vapor source released a continuous concentration of amphetamine vapor while an array of air samplers was deployed nearby. The field layout plan showing the arrangement of the sampling poles with respect to each other and to the amphetamine vapor source is presented in Figure 3. The sampling poles were arranged downwind from the source, and the air samplers were placed on the poles at a height of 1 m. The source was near the ground; nitrogen was used as the carrier gas and was maintained at a flow of 40 mL/min. Ambient air was drawn through the adsorption tubes by means of a small diaphragm pump at flow rates of up to 1L/min for 60 min. The pumps were powered by a rechargeable battery pack. The wind velocity was measured by using a Datametrics hot-wire anemometer. Experimental data for the field sampling test are given in Table I. RESULTS AND DISCUSSION Adsorbent Trap. A number of materials were examined as possible adsorbents for trapping amphetamine vapors. Silica gel and activated charcoal strongly retained the amine vapors which could not be released by thermal desorption. Tenax-GC (35-60 mesh) was tested and proved to be an adequate adsorbent (11). Flow rates of the order of 1 L/min were easily achieved. No loss of amphetamine occurred through 30 mg of the packing when sample volumes of up to 120 L were taken with the vapor source in the laboratory using high-purity nitrogen or air test streams. The mean recovery
ANALYTICAL CHEMISTRY, VOL. 57, NO. 7, JUNE 1985
ADSORBER I
r-----I,
1
I
ADSORBER 11
ADSORBER II ULTRABO ND PEG S
ADSORBER Tl U L T R A 6 O N D PEGS
LIME\
SODA TENAX-GC1
S E P TUM
1.
SAMPLE TRANSFER OR SEPTUM INJECTION
1487
c,
\
,/
SEPTUM
Ibl SAMPLE ANALYSIS OR STANDBY MODE
Figure 2. Schematic view of the gas chromatograph. C,, C1, carrier streams; V, vent to ambient. of amphetamine from Tenax over the range 20-50 ng was greater than 90%; the desorption temperature of ca. 250 O C was low enough to prevent decomposition while providing a desorption time which was sufficiently short to allow for a 4-min total analysis cycle. Effect of Ambient Air. While Tenax proved to be an efficient and suitable adsorbent for amphetamine under laboratory conditions, serious losses occurred when similar experiments were repeated by using ambient air. It was observed that after purging the spiked adsorber with 6 L of ambient air, no trace of amphetamine could be detected on the chromatogram. The above experiments were repeated by using a backup Tenax cartridge in series with the first (spiked) cartridge. After purging with 6 L of ambient air, the adsorption tubes were analyzed in the usual manner. No amphetamine peak could be observed on either chromatogram. It was therefore concluded that amphetamine did not elute from the first adsorbent but was probably irreversibly retained on the Tenax due to the effect of acidic impurities present in ambient air. Two-Component Adsorbent Sampling System. AndrC! and Mosier (14) reported a gas chromatographic system capable of analyzing aqueous solutions of salts of short-chain aliphatic amines. In that system the GC inlet was modified with a short Ascarite precolumn for releasing the free amines from their salts. The experiment described in the previous section with the Tenax adsorber was repeated by using a two-component sample adsorption tube similar to that shown in Figure l b but with Ascarite in place of the soda lime. Twenty-four nanograms of amphetamine in n-hexane were deposited with a syringe on the Ascarite in the front end of the tube, and 6 L of ambient air was drawn through the tube. The recovery of amphetamine from this adsorber after air sampling was quantitative. However, upon exposure to moisture and COz, Ascarite lost its granular shape, creating a significant flow restriction in the adsorber. The alkaline material (necessary for filtering acidic impurities) without this drawback was found to be sodium calcium hydrate (soda lime). Sampling System Desorption. Following sampling, the adsorption tube was reinstalled in the gas chromatograph,soda lime end facing the carrier stream, and purged with a stream of helium carrier gas for 40 s at 250 "C (standby mode, Figure 2b). Tenax acted as a short chromatographic column. It retained amphetamine while allowing water vapor and lowboiling volatiles to be vented to ambient, thus protecting the chromatographic column from excess moisture. After 40 s the carrier stream was redirected by the six-port switching valve to the second adsorber (sample transfer mode; Figure 2a), from which the amphetamine was subsequently injected, as a
(+lO,O)
0 5m
H
SOURCE : io0 mg OF AMPHETAMINE, CARRIER GAS IS NITROGEN AT 4 0 mL/min
SAMPLERS
SOURCE
5rn
-5,O)
Figure 3. Field layout pian indicating the arrangement of the air samplers with respect to the vapor source. narrow plug, into the column (sample analysis mode; Figure 2b). The two-component sample adsorption tube could be used repeatedly, although the buildup of interfering material was noted over long periods of time. Replacement of the used soda lime with fresh material, followed by conditioning as described above, eliminated the problem, permitting continued use of the more costly Tenax material. Two-Component Adsorbent Laboratory Tests. The soda lime packing was shown to have no influence on either the collection efficiency or the recovery of amphetamine compared to the Tenax-GC system. The plot of the measured vapor concentration at the sampling port of the vapor source (cf. ref 11)as a function of the sampling flow rate was found to be linear with a correlation coefficient of 0.998. The recovery of amphetamine from the two-component adsorbent system was 92.3% with 3.5% relative standard deviation at the 48-ng level. Field Sampling. A preliminary field sampling test was carried out as described above. Gas chromatographic analysis
14aa
Anal. Chem. 1985, 57, 1488-1490
amine in air has been developed. The technique offers a simple means of collecting air samples by using a novel twocomponent solid adsorbent system, and a fast analysis by thermal desorption directly into a GC equipped with an NPD. The key analytical features responsible for the good sensitivity and low background effects achieved include the selectivity of the NPD, the physicochemical properties of the soda lime/Tenax-GC adsorbent, and the advantages of the two-stage thermal desorption system.
2 m x 3 . 2 m m O.D.,
3% O V - I ON ULTRA BOND 2 O M (100-120 M E S H ) - 160°C
n
I6O
Registry No. Amphetamine, 300-62-9.
LITERATURE CITED u
0
I 2 3 4 5 MINUTES
I_LL--IL_I
0 1 2 3 4 MINUTES
5
Figure 4. Chromatograms of desorbates from (a) sampler no. (-5,O) and (b) sampler no. (+5,1). of the desorbates indicated that amphetamine was collected efficiently on sampler no. (+5,1) and only a trace quantity was collected on sampler (+5,0) (Figure 3). This was not unexpected since the mean wind direction during the 60-min sampling period was estimated to be southeast. The amount of amphetamine collected on sampler (+5,1) and measured chromatographically (Figure 4) compared well with the value estimated by using the turbulent diffusion equation for a steady emitting source near the ground (15). The detection limit with the present two-component adsorber configuration of amphetamine vapor in ambient air, based on a signal-to-noise ratio SIN >3, corresponds to 5 ppt or 0.03 bg/m3 amphetamine, in a 65-L air sample.
CONCLUSIONS A method for the detection of trace amounts of amphet-
(1) Lawrence, A. H.; MacNeil, J. D. Anal. Chem. 1982, 5 4 , 2385-2367. (2) Fishbein, L. "Chromatography of Environmental Hazards"; Elsevier: New York, 1982; Voi. IV, p 311. (3) Baker, J. K. Anal. Chem. 1977, 49,906-906. (4) Dalene, M.; Mathiasson, L.; Jonsson, J. A. J . Chromatogr. 1981, 207, 37-46. (5) Audunsson, G.; Mathiasson. L. J . Chromatogr. 1983, 261, 253-257. (6) Kuwata, K.; Akiyama, E.; Yamazaki, Y.; Yamazaki, H.; Kuge, Y. Anal. Chem. 1983, 55, 2199-2201. (7) Wood, G. 0.: Nichols, J. W. LASL Project R-059, NIOSH-IA-77-12 Report, LA-7295-PR, Los Alamos Scientific Laboratory, University of California, 1976. (8) Lovkvist, P.; Jonsson, J. A. J . Chromatogr. 1984. 286, 279-285. (9) Kashihira, N.; Makino, K.; Kirita, K.; Watanable, Y. J . Chromatogr. 1982, 239, 617-624. (IO) Kuwata, K.; Yamazaki, Y.; Uebori, M. Bunseki Kagaku, Shimpo Sosetsu 1980, 29, 170; Chem. Abstr. 1980, 92,220050. (1 1) Lawrence, A. H.; Elias, L.; Authier-Martin, M. Can. J . Chem. 1984, 62,1886-1888. (12) Predmore, D. B.; Christian, G. D. Anal. Chem. 1976, 4 8 , 361-363. (13) Lawrence, A. H.; Elias, L. Canadian Patent Application No. 429803, June 6, 1963. (14) Andr6, C. E.; Mosier, A. R. Anal. Chem. 1973, 4 5 , 1971-1973. (15) Crabbe, R. S. NRC DMEINAE, Quarterly Bulletin, National Research Council, 1973, Ottawa, Canada.
RECEIVED for review November 21,1984. Accepted February 4, 1985. Presented in part at the ACS Symposium on Analytical Methods in Forensic Chemistry, April 29-May 2, 1985, Miami, FL.
Preparation of Chelex-100 Resin for Batch Treatment of Sewage and River Water at Ambient pH and Alkalinity J a m e s A. Buckley
Metro Water Quality Laboratory, 410 West Harrison Street, Seattle, Washington 98119 The chemistry of trace metals in natural waters and sewage is influenced bv DHand alkalinity (1-5). Moreover, the uptake of trace metals 6y Chelex-100 ispH-dependent (6, 7). 1; this laboratory, equilibration with Chelex-100 of samples of river water Or sewage by the batch method (8) in a substantial increase in pH above ambient levels, an increase that was believed due to wash out of free OH- from the resin pore structure. Extensive washing with deionized water was only partially successful in controlling the elevation in pH but suggested that using a buffer wash might be more successful. In the following report, the work described in ref 9 and 10 regarding pH reduction in Chelex-100 column effluent provided part of the rationale for the development of the following method in which ambient levels of pH and alkalinity are maintained in water samples equilibrated with Chelex-100 which has been prewashed in acetate buffer of predetermined concentration.
EXPERIMENTAL SECTION Materials. Analytical-grade Chelex-100 resin (Bio-Rad Laboratories, control 25633), 50-100 mesh, in the Na form was used 0003-2700/85/0357-1488$01.50/0
in units of 0.5 g (as weighed from the original container, moisture content 68% to 76%) per 100 mL of buffer or 50 mL of water sample. A stock 3.5 M acetate buffer solution of pH 4.7 was prepared from 238 g of sodium acetate trihydrate dissolved in deionized water(DW), to which was added 102 mL of glacial acetic acid. The solution was then diluted to L, This stock buffer was diluted to 0.5 M for daily use. River water samples were collected from the Green-Duwamish River near Renton, WA. Sewage samples were collected from a secondary clarifier at the Municipality of Metropolitan Seattle's Renton Treatment Plant-a secondary-treatment, activatedsludge-process plant. Procedure for Washing of Chelex Resin in 0.5-g Units. The 0.5 M buffer was diluted with DW to the desired concentration in a 100-mL volumetric flask, and the diluent transferred to a 150-mL beaker containing a 2.5-cmstir bar, Then o.5 of Chelex was added, and the beaker was placed on a mag-mixset at ficient speed to keep the resin in suspension. After 15 min (unless other time specified),the resin was recovered on a 5-in., S&S No. 123 filter-sub placed in a glass-powder funnel. While still on the filter-sub the resin was rinsed with 400-500 mL of DW for 3 min, removed from the funnel, and drained on paper towels for 12 min. 0 1985 American Chemical Society
