Showing papers by "Purnendu K. Dasgupta published in 1990"

Formaldehyde Measurement Methods Evaluation and Ambient Concentrations During the Carbonaceous Species Methods Comparison Study

Abstract: During the Carbonaceous Species Methods Comparison Study at Glendora, CA, six groups made independent measurements of ambient formaldehyde concentrations during the period August 11–21, 1986. Measurement methods included DNPH-impregnated cartridges, an enzymatic technique, a diffusion scrubber, Fourier transform infrared spectroscopy (FTIR), differential optical absorption spectroscopy (DOAS), and tunable diode laser absorption spectroscopy (TDLAS). Sufficient data were obtained over the 10-day period to assess differences among methods based on hourly averages, 4- and 8-hour time-integrated sampling periods, and 3–5-minute averaging times. Comparison among the three spectroscopic methods (DOAS, FTIR, and TDLAS) showed good agreement, within 15% of the mean of the three methods for 162 hourly values. The enzymatic technique and diffusion scrubber reported concentrations ∼ 25% higher and 25% lower than the spectroscopic mean, respectively, for the entire study period. The DNPH cartridges, the only routine ...

Method and apparatus for generating a high purity chromatography eluent

Abstract: Apparatus suitable for generating a high purity, aqueous product stream including one or more selected ionic species and using it as a chromatography eluent, comprises eluent generating means defining a source channel and a product channel, and comprises a permselective ion exchange membrane partitioning said source channel and product channel, said ion exchange membrane including exchangeable ions of the same charge as said selected ionic species and allowing transmembrane passage to ions of the same charge as said exchangeable ions and being resistant to transmembrane passage of ions of the opposite charge, means for applying an electrical potential between said source channel and product channel, chromatographic separating means, conduit means for directing aqueous product stream from said product channel to said chromatographic separation means, and means for supplying a liquid sample to said chromatographic separating means.

Amperometric microsensor for water

Abstract: A thin film of a perfluorosulfonate ionomer (PFSI) is supported upon two electrodes. The positive electrode is composed of a noble metal. The polymer film has high affinity for water and certain other highly polar molecules, notably alcohols. When a voltage above the threshold of electrolytic breakdown potential of such a compound is applied across the film, the compound partitioned into the film can be electrolytically decomposed. Provided that the electrolytic breakdown products have a high enough vapor pressure to spontaneously leave the film, a versatile sensor, with a current output related to the analyte concentration, is formed. Sensors fabricated from available PFSI materials and functioning in this manner behave essentially as sensors specific for water and the lower alcohols.

Diffusion scrubber-based field measurements of atmospheric formaldehyde and hydrogen peroxide

Abstract: Field measurements were conducted to determine atmospheric concentrations of HCHO and H2O2 with automated instrumentation that relies on diffusion-based collection of water-soluble gases by an aqueous absorber flowing through a hydrophobic porous membrane tube. These measurements were made as part of the Carbonaceous Species Methods Comparison Study (CSMCS) at Cirrus College, Azusa, CA, during August 12–20, 1986. Both HCHO and H2O2 showed marked diurnal cycles, decreasing at night (to a minimum of 2–4 ppbv for HCHO, and near the detection limit, ∼ 30 pptv for H2O2) and increasing to a maximum in the late afternoon (15–19 ppbv for HCHO, ∼ 2 ppbv for H2O2). For the most part, the instrumentation performed unattended as designed; however, particle deposition in sampling lines and in the membrane-based diffusion scrubbers suggest that in-line losses can be significant for continued sampling of ambient air containing a relatively high concentration of particulate matter. Periodic (e.g., daily or every 2 days) ...

Measurement of acid dissociation constants of weak acids by cation exchange and conductometry

Abstract: A simple strategy is presented for the determination of acid dissociation constants based on the measurement of conductance of a known concentration of the acid and/or the conductance of a solution of its fully or partially neutralized alkali-metal salts. For an n-protic acid, 2n conductance measurements are minimally necessary. In the simplest case of a typical monoprotic acid, the conductance of its alkali salt solution is measured before and after passage through an H{sup +}-form exchanger. From these data both the pK{sub a} of the acid and the equivalent conductance of the anion can be computed. The underlying equations are rigorously solved for monoprotic acids and some diprotic acid systems. For other diprotic and multiprotic acid systems, initial estimates are obtained by making approximations; the complete data set is then subjected to multiparametric fitting. The method does not require pH measurements; conductance can generally be measured accurately at low enough ionic strengths to obviate the need for major activity correction. Several experimental measurements are presented and excellent agreement with literature pK{sub a} values is observed. The reliability of the equivalent conductance values computed in this fashion is limited, however.

Novel approaches to ionic chromatography

Abstract: Research during this reporting period, continued on ionic chromatography. Major progress has been made towards on-line on-demand generation of ultrapure chemicals by electrochemical means. The concentration of the generated material is governed electrochemically.