Showing papers by "Purnendu K. Dasgupta published in 1986"
TL;DR: The predictions of the corresponding equation are in good agreement with the vapor pressure data obtained by Blair and Ledbury at aqueous concentrations as high as X/sub HCHO/ = 0.254 (13.4 M).
Abstract: Stable concentrations of gaseous formaldehyde (atm) may be generated at the 10/sup -9/-atm level and up by equilibration of air with an aqueous formaldehyde (M) solution through a microporous membrane tube The solubility behavior of formaldehyde at 2932 K obeys the equation (HCHO(aq)) = 16650(HCHO(g))/sup 10798/ for HCHO(g) ranging from 33 x 10/sup -9/ to 13 x 10/sup -6/ atm or HCHO(aq) ranging from 10 x 10/sup -5/ to 69 x 10/sup -3/ M When the aqueous concentration is expressed in mole fraction units, the predictions of the corresponding equation are in good agreement with the vapor pressure data obtained by Blair and Ledbury at aqueous concentrations as high as X/sub HCHO/ = 0254 (134 M) At low HCHO concentrations, the temperature dependence between 2782 and 2982 K is given by (HCHO(aq)) = 10/sup ((4538/T)-1134)/ (HCHO(g))/sup ((2522/T) + 02088) with an uncertainty of less than 10%
129 citations
TL;DR: In this article, the equilibrium gas phase concentration of ammonia in dilute solution has been measured as a function of total ammonia + ammonium concentration (0.002-0.10 M), pH (6−10) and temperature (278.8−290.6 K).
120 citations
TL;DR: In this paper, a flow injection system based on the p-hydroxyphenylacetate-peroxide-peroxidase reaction allows the simultaneous determination of H/sub 2/O/Sub 2/ and CH/sub 3/HO/sub2/ at 50 samples/h with an LOD of 0.1 /sup +/g/L (3 nM).
Abstract: A flow injection system based on the p-hydroxyphenylacetate-peroxide-peroxidase reaction allows the simultaneous determination of H/sub 2/O/sub 2/ and CH/sub 3/HO/sub 2/ at 50 samples/h with an LOD of 0.1 /sup +/g/L (3 nM) H/sub 2/O/sub 2/. A pressurized porous PTFE membrane reactor introduces the enzyme, and the pH of the flow stream is altered by introducing NH/sub 3/ through a nonporous cation exchange membrane reactor. Excellent reproducibility, precision, and sensitivity are achieved with the membrane reactors and an inexpensive filter fluorometer with a monochromatic excitation source. Low levels of residual peroxide in water are ubiquitous; such levels return soon after the H/sub 2/O/sub 2/ is catalytically removed.
103 citations
TL;DR: In this paper, a diffusion scrubber, employing a porous fluorocarbon membrane as the sampling tube and with a scrubber solution flowing into a narrow annular space exterior to the membrane, is described.
Abstract: A diffusion scrubber, employing a porous fluorocarbon membrane as the sampling tube and with a scrubber solution flowing into a narrow annular space exterior to the membrane, is described. The use of this diffusion scrubber with a dilute buffered formaldehyde solution as the scrubber solution has been exploited for collecting sulphur dioxide. Collection efficiencies are reported for sampling rates of up to 3 l min–1. The response time to a SO2 input pulse in the continuous analysis mode is demonstrated using dilute hydrogen peroxide as the scrubber solution and a conductivity detector. The advantages of a diffusion scrubber for collecting atmospheric gases are discussed. A simple inexpensive design of permeation tubes for standard gas sources is also reported.
36 citations
TL;DR: In this paper, the preservation of sulfite, sulfide, and methanethiol in buffered formaldehyde and oxaldihydroxamic acid stabilizers has been studied, and flow injection analysis procedures that involve T mixing or membrane-based reagent introduction have been developed for the fast (24 samples/h) analysis of these anions based upon the reaction with N-acridinylmaleimide in a water-N,Ndimethylformamide medium to form a fluorescent product.
Abstract: Preservation of sulfite, sulfide, and methanethiol in buffered formaldehyde and oxaldihydroxamic acid stabilizers has been studied. Flow injection analysis procedures that involve T mixing or membrane-based reagent introduction have been developed for the fast (24 samples/h) analysis of these anions based upon the reaction with N-acridinylmaleimide in a water-N,N-dimethylformamide medium to form a fluorescent product. Detection limits are 0.04, 0.60, and 0.80 ..mu..M, respectively, for the three sulfur species; differential analysis is possible.
35 citations
TL;DR: The dissociation constant for the aqueous equilibrium OHCH 2 SO 3 − = HCHO + HSO 3 − (where HCHO includes the hydrated form) has been determined via vapor pressure measurements to be 1.17 ± 0.14 × 10 −7 at pH 4 and 293 K, in excellent agreement with kinetic and spectroscopic measurements as discussed by the authors.
34 citations
TL;DR: In this paper, a carrier sample buffer system is selected for a proton-ligand system with multidimensional spectral detection, which is critical in flow injection analysis and is discussed in detail.
Abstract: Controlled dispersion as generated in flow injection analysis permits essentially infinite known compositional variations. If carrier-sample compositions are appropriately chosen, reasonably accurate values of equilibrium constants are easily obtained in proton-ligand and metal-ligand systems with multidimensional spectral detection. Choice of an appropriate carrier-sample buffer system is critical in proton-ligand studies and is discussed in detail. Metal-ligand association constants are reliably obtained with both high and low conditional stability constants. 10 references, 4 figures.
28 citations
TL;DR: Fluorescence enhancement of 8-hydroxyquinoline-5-sulfonic acid complexes of Mg, Ca, Sr, Ba, Al, Zn and Cd were studied in micellar and hydroorganic solvents.
Abstract: Fluorescence enhancement of 8-hydroxyquinoline-5-sulfonic acid complexes of Mg, Ca, Sr, Ba, Al, Zn and Cd were studied in micellar and hydroorganic solvents Al is extraordinarily amenable to both types of fluorescence enhancement, an order of magnitude to two order of magnitude enhancement of fluorescence intensity has been observed with aqueous hexadecyltrimethylammonium chloride (HTAC) and certain mixed aqueous-organic solvents Fe(III) appears to be an unusually powerful fluorescence quencher in these systems — the effect is noticeable in low micromolar concentrations and is greatly amplified by cationic surfactants such as HTAC
18 citations
TL;DR: In this paper, the authors describe an annular perfluorosulfonate (Nafion) dual tubular membrane assembly where inside of the inner membrane tube and outside of the outer membrane tube are packed with ion exchange resin beads.
14 citations
TL;DR: A single flow channel analysis system that employs the formaldehyde-S(IV)-pararosaniline color reaction has been developed for the determination of aqueous S(IV).
Abstract: A single flow channel analysis system that employs the formaldehyde-S(IV)-pararosaniline color reaction has been developed for the determination of aqueous S(IV). The system employs a passive cation-exchange membrane reactor for the introduction of base and a pressurized porous membrane reactor for the introduction of acidic pararosaniline. The detection limit is 1.6 x 10/sup -7/ M S(IV); the sample size is 200 ..mu..L, and the throughput rate is 15/h. Results for cloudwater samples are presented. 15 references, 3 figures, 1 table.
13 citations
TL;DR: In this paper, the Berthelot reaction using NaOCl and ammonia to form indophenol blue, monitored at 660 nm with a light emitting diode-based detector.
Abstract: Flow injection analysis (FIA) has been applied to the determination of total phenol and total alkali in high concentration alkaline phenoxide liquors as it occurs in industrial process streams. The total alkali content and total phenol content in samples containing 20–50% (w/v) sodium phenoxide can be directly measured without mutual interference. The first is measured by peak width measurement based FIA with conductimetric detection utilizing an electronic circuit to permit automatic measurement from minima to minima. The total phenol is measured by the Berthelot reaction using NaOCl and ammonia to form indophenol blue, monitored at 660 nm with a light emitting diode-based detector.