SummaryThe FPD and the new SCD have been examined for their respective performance characteristics as sulfur selective detectors for HRGC in the determination of atmospheric sulfur gases. Overall, the SCD was an extremely selective and sensitive sulfur gas detector with lower MDLs than the FPD and fewer problems with interferences and noise stability, thus allowing the SCD more flexibility in capillary column selection. Modification of the FPD, however, provided more symmetrical peaks and greater resolution than the Sievers Model 350 SCD.
This sensitive, albeit precarious, method for measuring ppb-ppt (V/V) concentrations of H 2 S was examined for various sources of potential error within the procedure. Filter preparation, filter storage, filter extraction, fluorimetric reagent stabilities, matrix differences between standards and samples, and possible interferences from other sulfur-containing compounds were separately studied for their effects on the analytical performance of the method. The overall method showed no Interference from SO 2 , CS 2 , COS, CH 3 SH, CH3SCH3, and SO 4~2 . To minimize bias and obtain a reliable estimate of precision, the method should be calibrated with H 2 S standards rather than liquid bisulfide standards. The measurement precision is a function of the quantity of H 2 S collected as Ag 2 S and/or AgSH on the impregnated filters. Because of the method's linear dynamic range, sufficient air should be sampled to achieve filter loadings of 15 to 35 ng S/filter. A quality control method based on fluoresceln mercuric acetate (FMA) is presented that ensures data quality while reducing the otherwise frequent need for fluorimetric calibration.A sensitive method for measuring low and sub-parts-perbillion (ppb V/V) concentrations of atmospheric hydrogen sulfide has been described by Natusch et al. 1 and modified by Jaeschke et al. 2 for automated field sampling. The method employs the collection of H2S on a AgNCVimpregnated filter. The filter is then leached with a basic cyanide solution to liberate the sulfide collected as Ag2S and/or AgSH on the filter. Quantification is achieved by the selective quenching effects of sulfide [S"~2] (or more correctly bisulfide [HS~] since pK2 = 19 ± 2 for H2S( aq ) 3 ) on the fluorescence of fluorescein mercuric acetate (FMA). This fluorimetric procedure was initially described by Karush et al.,4 Grunert et al., 5 and Axelrod et al. 6The work described in this paper was performed as a portion of a more comprehensive evaluation of potential analytical techniques to measure natural emissions of volatile sulfur compounds. 7 The major objectives for the specific evaluation of the AgNCVfilter/FMA fluorimetric method were to: a) compare the responses of liquid sodium sulfide standards, which are normally used to calibrate the method, with gaseous H2S standards, which better simulate actual analyte and sample matrix components; b) clarify previous conflicting reports 1 ' 2 ' 8 concerning potential positive interferences from CH3SCH3 and CH3SH; c) assess the sources and magnitudes for both indeterminate and systematic errors in the sampling and fluorimetric procedures; and d) suggest modifications to the basic method and/or operational procedures that improve both analytical ruggedness and data quality. Experimental Methods ApparatusAn Aminco-Bowman spectrophotofluorometer with an analog readout was used for the fluorimetric determinations. The excitation and emission wavelengths were 499 nm and 520 nm, respectively. Conventional fused silica cuvettes were used for the fluorimetric measurements. A...
A metal foil collection/flash desorption/flame photometric detection (MFC/ FD/FPD) technique was used by investigators from the University of Idaho (UI) to measure ambient total sulfur gas concentrations from an aircraft platform during the NASA Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation 3 (GTE/CITE 3) program. The MFC/FD/FPD technique allowed rapid quantitation of tropospheric background air masses using sample integration times of 1-3 min with little or no gap between measurements. The rapid and continual sampling nature of this technique yielded data covering approximately 75% of the entire CITE 3 program's air track. Ambient air measurement data obtained during northern hemisphere (NH) flights often exhibited relatively high total sulfur gas values (up to 19 ppb) and an extremely high degree of sample heterogeneity, especially in coastal locations. Data from southern hemisphere (SH) flights typically exhibited relatively low total sulfur gas concentrations and a low degree of sample heterogeneity. A bimodal interhemispheric total sulfur gas gradient was observed using data obtained during transit flights between the two CITE 3 program ground bases. Comparisons were made of UI total sulfur gas measurements with composite sulfur gas values generated using speciated sulfur gas measurements from other CITE 3 participants. Only a relatively small number of overlap periods for comparison were obtained from all the available CITE 3 data because of large differences in measurement integration times and lack of synchronization of sample start/stop times for the various investigators. These effects were compounded with extreme sample heterogeneity in the NH and the speed at which the aircraft traversed the air masses being sampled. Despite these constraints, sufficient overlapping data were available for the comparative evaluations. Comparison of NH UI total with composite sulfur gas values showed excellent correlation and linear curve fit, indicating substantial qualitative agreement. Simple linear regression of total on composite sulfur gas data yielded a slope of 1.9 for coastal NH regions and 1.2 for marine NH regions. The marine NH slope is not statistically different from one, indicating substantial quantitative agreement between UI total and composite sulfur gas values in these regions. However, a significant difference was observed when these same data were treated with a paired t test. SH data exhibited no significant correlation or linear regression slope. A paired t test showed a statistically significant difference when all SH flights were used. However, data from three SH flights that were classified into a unique group using discriminant analysis showed no significant difference between UI total and composite sulfur gas values when analyzed with the paired t test.Paper number 95JD00197. 0148-0227/95/95JD-00197505.00 pounds. Estimation of natural source strengths and atmospheric concentrations of sulfur gases is complicated by lack of data over large portions of the globe, ...
Summary Table 1 A diverse mixture of volatile headspace anatytes containing compounds with boiling points covering a range from -196°C to Anawes, their boiling points, and their concentrations in the standard gas mixtures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.