Following the administration of bromazepam, no metabolites are found in the blood (7); therefore, D P P (see Figure 4) can be used without employing thin-layer chromatography to ensure specificity. Blood samples taken a t 6 hours on days 1, 4, 9, 10, 12, and 15 from a subject who received an oral dose of 3 mg of bromazepam daily were analyzed by the polarographic assay described above. The assay has a recovery of 62.1% f 7.8 (std dev) in the range of 10-1000 ng bromazepam/ml of blood. Internal and external calibration curves for bromazepam are shown in Figure 5 . The same samples were also analyzed employing the EC-GLC previously reported ( 7 ) . The data in Table I1 show good agreement between the two assays. Although the chromatographic assay is more specific than the polarographic assay, both assays have essentially the same absolute limit of detection.
CONCLUSIONS Using the conventional type of cell, the absolute limit of detection of differential pulse polarographic analysis for two 1,4-benzodiazepines was increased to 10 ng of compound by miniaturization of the cell and its operational electrodes. Further increases in detection limit will only be possible through radical changes in cell design, choices of electrodes, and more sophisticated instrumentation, incorporating signal processing to increase the signal-noise ratio.
ACKNOWLEDGMENT The authors extend thanks to J. Arthur F. de Silva for his critical review of this manuscript, and to Robert McGlynn for the drawings of the figures presented.
LITERATURE CITED (1) M. A . Brooks, J. A. F. de Silva, and M. R . Hackman, Amer. Lab., 5(9), 23-38 119731 (2) M. A. Brooks, J. A. F. de Sllva, and L. M. D'Arconte, Anal. Chem., 45, 263-266 (1973). (3) M. ~ A .Brooks, J, A. F. de Silva, and L. D'Arconte, J. Pharm. Scl., 82, 1395-1397 (1973). (41 M. A . Brooks, J. A. F. de Silva, and M. R. Hackman, Anal. Chlm. Acra. 84, 165-176 (1973). (5)J. A. F. de Silva, N. Munno, and N. Strojny, . . J. Pharm. Sci., 59, 201-210 (1970). (6)J. A . F. de Silva, and M. R. Hackman, Anal. Chem., 44, 1145-1151 (1972). (7) J. A . F. d e Silva, I. Bekersky, M. A. Brooks, R . E. Welnfeld, W. Qlover, and C.V. Pugllsl, J. Pharm. Scl,, 63, 1440-1445 (1974). (8) J. A. F. de Silva, C. V. Puglisl, M. A. Brooks, and M. R . Hackman, J. Chromatogr.,99, 461-483 (1974). 19) J. A. F. de Sllva. I. Bekerskv. and M. A. Brooks, J. Pharm. Scl., 83, 1943-1945 (1974). M. R. Hackman, M. A. Brooks, J. A. F. de Silva, and T . S Ma, Anal. Chem., 48, 1075-1062 (1974). M. A. Brooks, J. J. Bel Bruno, J. A. F. de Silva, and M . R. Hackman, Anal. Chlm. Acta, 74, 367-385 (1975). S. A. Kaplan, J. A . F. de Silva, M. L. Jack, K. Alexander, N. Strojny, R . E. Welnfeld, C.V. Pugllsi, and L. Welssman, J. Pharm. Scb, 62. 19321935 (1973).
__ _ _
\
- I
RECEIVEDfor review March 18, 1975. Accepted June 16, 1975. Presented a t the 26th Annual Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 3-7, 1975.
Determination of Submicrogram Amounts of Atmospheric Particulate Sulfur Janja D. Husar, Rudolf B. Husar, and Pamela K. Stublts Air Pollution Research Laboratory, Department of Mechanical Engineering, Washington University, St. Louis, Mo. 63 130
The rate and formation mechanism of particulate sulfur in urban atmospheres is one of the intriguing problems of current environmental research. From the point of view of analytical chemistry, the study of sulfate formation in power plant and urban plumes is made difficult because of the short sampling times and consequently small amounts of particulate matter available for analysis. Thus, a strong need exists for an accurate means for determination of particulate sulfur in submicrogram quantities. One of the promising techniques for this purpose is thermal decomposition of particulate sulfur compounds to gaseous products and subsequent detection by flame photometric detector (FPD). The first to use this approach were Scaringelli and Rehme ( 1 ) who slowly heated and vaporized the sample in a furnace. Roberts and Friedlander (2) placed filter sections between two stainless steel strips and rapidly vaporized the sulfur compounds by capacitor discharge. We have applied the technique for the sulfur analysis of filter samples collected in plumes by aircraft as part of the St. Louis Regional Air Pollution Study (RAPS). In the course of the aircraft sample analyses, a need arose for detailed documentation of the technique, to improve its reproducibility, and to lower the detection limit beyond those reported by earlier investigators. 2062
In this paper, we report the adapted procedures for routine sample analyses, calibration data for a variety of sulfur compounds believed to exist in the atmosphere, sensitivity, precision, sample recovery, and comparison results with X-ray fluorescence (XRF).
EXPERIMENTAL Reagents. Reagent grade chemicals were used throughout this study without further purification. Apparatus. The sulfur determining system is shown schematically in Figure 1. It consists of a flash vaporization vessel, flame photometric detector, electronic integrator, and a strip chart recorder. The sample vaporization was performed by capacitor discharge (0.38 F, 12 V) across a tungsten boat, resulting in resistance heating to 1100 OC. Commercially available tungsten boats (E. Fullam Inc., Schenectady, N.Y. 12301, Catalog number 1213, for electron microscope evaporator supplies) were utilized. Proper electrical contact between the supporting metal posts and the boat was ensured by two sets of bolts. The vaporization vessel that houses the tungsten boat was designed to withstand large rates of temperature change. For that purpose, the metal posts that support the tungsten boat were sealed in the bottom part of the vaporization vessel by glass to metal seals (Latronics Co., Latrobe, Pa. 15650), both having the same coefficient of thermal expansion. Vaporized gaseous decomposition products of sulfur compounds were carried to the flame photometric detector by a stream of clean, charcoal filtered air at a flow rate of 2 cm3/sec. The volume
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
L T O PUMP
r-
RECORDER
Figure 1. Schematic of the sulfur detection system consisting of t h e flash vaporizer, Meloy SA-160 flame photometric detector, strip chart recorder, and the peak area integrator
i
._,
\
,
5 SULFUR
Figure 3.
IO
I5
COXENTRATION, p l / m l
Calibration data for peak area vs. sulfur concentration
(0)H 2 S 0 4 ; (A)(NH4)&04;(0) NH4HSO4; ( 0 )( N H ~ ) Z S O ~ * Z ~ (0 SO )ZnSO4 ~;
101982 ,
peaks produced by repeated analyses of 3.2 wg/ml S as HzS04 solution is shown in Figure 2. As seen in Figure 2, the first flash accounts for 94% of the detected sulfur while the second and third flashes contributed 4 and 2%, respectively. The tungsten boat withstood an average of forty analyses, with three discharges per analysis.
104 ,803 1-
RESULTS A N D DISCUSSION
TIME
MINUTES
Figure 2. Strip-chart recording of peaks produced by repetitive analysis of 3.2pg/ml S as H2S04
The numbers indicate the integral of the respective peaks as obtained
by the
electronic integrator
of the apparatus through which vaporized sample travels to the detector was minimized by 20-cm long Teflon tubing (0.015-cm id.), connected directly between the vaporization apparatus and the detector. Because of transport, the time delay between the flash and the detector was 2 seconds. Most of this delay is due to the residence time in the vaporization vessel. The detector used was the Meloy SA-160 flame photometric total sulfur sensor. Its operation is based on the chemiluminescence of activated molecular sulfur species, produced in a hydrogen hyperventilated diffusion flame (3).The Meloy sulfur analyzer output is linearized and the sulfur content was registered directly on the strip chart recorder and the peak area integrated by an electronic integrator. Sample Preparation. Samples of ambient particulate matter were collected on light-weight glass fiber filter tapes (Pallflex E70/2075W, Pallflex Product Corp., Kennedy Drive, Putnam, Conn. 06260) and on Teflon filters (Mitex Filters, Millipore Co., Bedford, Mass. 017301. The filter deposits were extracted in 0.25 to 1 ml double distilled deionized water at 25 "C. Ammonium sulfate aerosol was generated in the laboratory by an ultrasonic nebulizer (EN-143, Mistozgen Equipment Co., Oakland, Calif. 94607) and deposited by filtration using a TWOMASS /%gaugeaerosol sampler ( 4 ) . Standards for calibration purposes were prepared in the range of 0.16 to 34.0 wg/ml sulfur as solutions of HzS04, (NH4)2S04, NH4HS04, (NH4)2S04-ZnS04.6HzO,ZnS04.7H20. Sample Analysis. Sample extracts and standard solutions were transferred with a 5-,1 microsyringe to the tungsten boat and heated at 60 " C for 30 seconds until dry. The residue was then vaporized by capacitor discharge. A strip-chart recording of three sets of
Calibration. T h e sulfur compounds reported t o be the dominant components of the submicrometer range urban aerosol are sulfuric acid, ammonium sulfate and bisulfate, zinc and zinc ammonium sulfate (5-8). Calibration curves, therefore, were obtained using standard solutions of these sulfates in the range of 0.16-34 pg/ml of sulfur. A set of calibration data is shown in Figure 3. T h e nonlinearity appare n t in the lower portion of the calibration curve is attributed to shorter peak tails a t lower concentrations. In ten seconds after the flash, 97% of the total count was recorded for 1.6 lg/ml S. On the other hand, for 6.4 wg/ml, only 84% of the total count was recorded in ten seconds. T h e difference is due to "tailing" effect at higher concentrations. Note the excellent correlation coefficient of 0.996 for t h e above five sulfates. T h e recovery of ammonium sulfate by the present method was shown to be 100% within the experimental error (see next section). T h e consistency of the calibration data of the other sulfur compounds with ammonium sulfate implies 100% recovery for ' these substances. T h e above sulfates are water soluble and have decomposition temperatures below 600 O C (9). When sodium sulfate standard solution was analyzed using this technique, only 35-45% sulfur was recovered. T h e tungsten boat probably attained t h e NaQS04 decomposition temperature only on certain spots and partial vaporization was accomplished. Alkaline sulfates are known to have decomposition temperatures of above 1200 O C (9) and they are not detectable by t h e present method. T h e lower detection limit of the method is given by the purity of the distilled water used and not by the sensor. A 5-pl sample of distilled deionized water gave a signal equivalent t o 0.3 f 0.05 ng sulfur, corresponding to a solution concentration of 0.06 pg/ml. Provided that ambient sampling is performed using a filter with low sulfur blank (e.g., Teflon filters, Pallflex glass fiber filter), sampling times on the order of minutes are adequate for meaningful sulfur determination. I t has been shown that this feature of the method makes it uniquely suitable for analysis of filter samples collected in plumes by aircraft ( 1 0 ) . Precision. T h e precision of the flash vaporization-FPD measurement was determined by consecutively analyzing replicate samples at concentrations of 0.6, 1.6, 3.2, and 6.4
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
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Table I. Comparison of Sulfur Values Obtained by Vaporization-Flame Photometric Detection Method ( F P D ) withThose Obtained by Gravimetric Weighing"
Table 111. Comparison of Sulfur Values Obtained by Vaporization-Flame Photometric Detection Method ( F P D ) with Those Obtained by X-Ray Fluorescence Methoda Sulfur
Sulfur, u g
S u l f u r us/crn2
P D ) RlUI
FPD
1 2 3 4 5 6
83.3 80.9 214.5 189.9 61.3 431.8
Gravimetric
a Regression equation i s tion coefficient of 0.996.
92.3 88.7 248.4 206.7 55.8 446.4 FPD =
0.96 G r a v .
% found
Sample
90.3 91.2 86.3 91.8 109.9 96.7
36Tb 37FC 38T 39F 40T 41F 42T 43F 44T 45F
- 4.87 w i t h correla-
Table 11. Recovery of Known Amounts of Sulfur as (NH4)zSOa Added to Samplesa S CUE
Sample
Added
Total
Recovered
so.
5
S
S
S
% S
7.04 6.84 6.77 6.59 6.96 5.95
2.98 2.84 3.39 3.36 3.02 2.73
96.3 91.9 109.7 108.7 97.7 88.3
F B F B F B
4.06 4.00 3.38 3.23 3.94 3.22
3.09 3.09 3.09 3.09 3.09 3.07
a Recovered sulfur m e a n viation from t h e m e a n 8.8%.
i 0.07 i
0.07
i 0.07
0.07 0.07 i 0.07 3.05 f 0.27 w i t h i f
Recovered
percent standard de-
wg/ml S as H2S04. Detailed precision tests were performed using 3.2 wg/ml S as H2S04 solution which yielded a standard deviation of 0.08 pg/ml S, that is 2.5%. The precision inferred from three consecutive analyses performed a t the other stated concentrations is also in the range of 2.5%. This precision test did not include the extraction procedure. The precision of the entire procedure, including the extraction step, would probably be poorer, by a factor of two. Sample Recovery. Two sets of recovery experiments were performed. In the first set, known quantities of sulfur, determined gravimetrically, were analyzed by FPD. Ammonium sulfate aerosols were generated from a 1% by weight water solution and subsequently collected on preweighed glass fiber filters. Following the aerosol sampling, filters were reweighed and the amount of deposited (NH4)$304 was determined. The filters were extracted in distilled-deionized water (25 O C ) and the extracts analyzed. The results given in Table I show that, on the average, 94.4 f 8.8% of the deposited (NH4)2S04 was actually recovered by the present analytical method. The corre!ation coefficient for these comparison experiments was 0.996. The observed deviations are due to both inaccuracies of gravimetric weighing as well as the sulfur determination. A second set of recovery experiments was performed by fortifying glass fiber filter sample extracts of ambient aerosol with 3.09 wg/ml of sulfur in form of ammonium sulfate solution, and subsequently reanalyzed. The average recovered sulfur was 3.05 Hglrnl. Detailed results are given in Table 11. The percent recovery is between 88 and 109%. Comparison w i t h X-Ray Fluorescence Analysis. Ten samples of size classified ambient aerosol, collected in St. Louis on Teflon filters, were analyzed by X-ray fluorescence (XRF) a t the Environmental Protection Agency's National Environmental Research Center, Field Methods Development Section. The method and the instrumenta2064
XRF
particulate sample, particle size 53 p m .
I ml I
Sample
40075 40075 40076 40076 40077 40077
FPD
2.92 4.74 3.23 5.09 3 -47 4.94 3.93 6.02 6.24 7.20 4.48 6.01 1.32 1.12 1.02 0.80 3.10 5.24 2 -83 4.01 a Regression equation i s FPD = 0.77 XRF - 0.23 w i t h correlation coefficient of 0.931. T = T o t a l particulate sample. CF = F i n e
ANALYTICAL CHEMISTRY, VOL. 47,
NO. 12,
tion were reported recently (7). The same samples were subsequently reanalyzed by the vaporization F P D technique and the results are given in Table 111. The data show a good correlation between the two methods, r = 0.931. However, sulfur concentrations obtained by X R F were found to be on the average higher by 23% than those obtained by vaporization FPD. At this point, we are not inclined to speculate about the source of the above discrepancy. We merely wish t o point out that the above two sets of determinations utilize fundamentally different detection methods and that they are different in their modus operandi. More extensive comparison studies are presently in progress. CONCLUSIONS The vaporization-FPD technique has been improved and adapted for the precise determination of submicrogram quantities of particulate sulfur. I t has been shown that, within the experimental error, the sulfur recovery for five sulfates commonly found in the atmosphere is 100%. The technique is uniquely suitable for analysis of filter samples collected in plumes by aircraft. ACKNOWLEDGMENT The authors thank W. E. Wilson for suggesting the method and for his illuminating comments; P. T. Roberts for setting up the apparatus and for his help to overcome initial difficulties; A. R. Stiles, T. G. Dzubay, and R. K. Stevens for the X R F analysis; R. A. Fletcher and E. S. Macias for ammonium sulfate sample preparation and gravimetric weighing; and P. K. Mueller for his helpful suggestions. LITERATURE CITED (1) F. P. Scaringelli and K. A. Rehme, Anal. Chem., 41, 707 (1969). (2) P. T. Roberts and S. K. Friedlander, presented at the conference on Health Consequences of Environmental Controls: Impact of Mobile Emissions Controls, Durham, N.C., April 1974. (3) D. P. Lucero and J. W. Paljug, ASTM Special Technical Publication 555, Philadelphia, Pa., 1974. (4) E. S.Macias and R . B. Husar, presented at the 2nd InternationalConference on Nuclear Methods in Environmental Research, Columbia, Mo.. July 1974. (5) C. E. Junge, J. Geopbys. Res., 65, 227 (1960). (6) M. 0.Amdur and M. Corn, Am. lnd. Hyg. Assoc. J., 24, 326 (1973). (7) T. G. Dzubay and R. K. Stevens, presented at the 2nd Joint Conference on Sensing of Environmental Pollutants, Washington, D.C., Dec. 1973. (8) R. J. Charlson, A. H. Vanderpol, D. S. Covert, A. P. Waggoner, and N. C. Ahlquist. Science, 164, 156 (1974). (9) A. G. Ostroff and R. T. Sanderson, J. horg. Nucl. Chem., 9, 45 (1959). (10) J. D. Husar, R . B. Husar, W. E. Wilson, J. L. Durham, W. Shepherd, J. Anderson, and S. Gregg, EPA Report, in press, 1975.
OCTOBER 1975
RECEIVED for review May 12, 1975. Accepted July 14, 1975. This research was supported by a grant from the U S . Environmental Protection Agency, National Environmen-
tal Research Center, Atmospheric Aerosol Research Section, under Grant Number R802815.
I CORRESPONDENCE
I
Criteria for Infrared Spectra Submitted to Journals Sir: The quality of infrared spectra presented in the literature is variable and it cannot always be evaluated by inspection. Yet it is of great importance t h a t such archival data be of sufficiently high quality to be useful in its intended context as well as for future reference. The purpose of these recommendations is to help ensure readable, reproducible spectra of sufficient accuracy to serve as documentation for the compounds scanned and as reference data for other users. Spectra that do not meet these minimum recommendations are open to serious questions as to their usefulness. These recommendations are based on more comprehensive criteria set forth by the Coblentz Society for evaluation of infrared spectra ( I ) . Instrumentation. Partial spectra may be used t o illustrate specific points, but infrared reference spectra should extend a t least from 4000 to 650 cm-l with no more than minor gaps (marked) from mulling agents or solvents. Commercial spectrometers should be functioning a t manufacturer’s specifications. Instrument parameters (slit, scan speed, gain) should be chosen to ensure accurate servo response ( 2 ) . Data demonstrating instrument performance, especially abscissa accuracy, should be described. Abscissa accuracy should be at least f 5 cm-l from 4000 to 2000 cm-l and f 3 cm-l a t wavenumbers less than 2000 cm-l. Frequency calibration is best obtained from indene ( 3 ) ; polystyrene or H20 and CO2 (single beam spectrum) are marginally acceptable. Unbalanced atmospheric absorption bands, noise level, and dead spot from a sluggish servo should correspond to less than 1%T . The strongest absorption bands should extend approximately from 90% T to 5 or 10% T . Reduction of normal reference beam energy by more than 50%from mechanical a t tenuation, reflection attachments, reference sample absorption, or other experimental conditions should be avoided or dealt with by increasing the slit width or scan time using the well-known “trading rules” ( 2 ) .The transmission background a t 2000 to 1800 cm-I should be about 90% with a range from 75 to 100% acceptable. Sample Preparation. For most group frequency inter-
pretations, it is desirable to obtain spectra in inert solvents (CCl4-CS2) when possible. Cell path length and window material, concentration, and solvent used should be recorded. Mineral oil and fluorocarbon mulls are preferred when solid state spectra are needed. Pressed halide discs, if used, should be moisture free, and due cognizance taken of possible artifacts arising from grinding and pressing. A KBr matrix should not be used for HC1 salts because of possible halide exchange. Spectra of all purified end products and of key intermediates in a synthesis should be submitted. Spectra of any model compounds prepared for comparison are very useful. Other pertinent data such as elemental analysis and NMR or UV spectra should be included, along with the structures and approved names of the compounds. Format. Original spectra or glossy high-contrast photographic copies are needed for reproduction. Redrawn spectra are rarely acceptable for publication.
LITERATURE CITED (1) Coblentz Society Board of Managers, Anal. Chem., 38 (9), 27A (1966). (2) W. J. Potts, Jr., and A. L. Smith, Appl. Opt., 6, 257 (1967). ( 3 ) R . N. Jones and A. Nadeau, Spectrochim. Acta, 20, 1175 (1964).
Clara D. Craver’ Chemir Laboratories 761 W. Kirkham Avenue Glendale, Mo. 63122
Jeanette G. Grasselli’ Sohio Research 4400 Warrensville Center Road Cleveland, Ohio 44128
A. Lee Smith2 Dow Corning Corporation Midland, Mich. 48640 Member, Joint Committee on Atomic and Molecular Physical Data. Chairman, Joint Committee on Atomic and Molecular Physical Data. RECEIVEDfor review July 10, 1975. Accepted July 10,1975.
ANALYTICAL CHEMISTRY, VOL. 47,
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OCTOBER 1975
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