Showing papers by "Purnendu K. Dasgupta published in 1992"
TL;DR: The use of hematin as catalyst and p-cresol as the substrate leads to a particularly inexpensive and sensitive system, permitting a limit of detection (LOD) of 7 nM H2O2 in a flow-injection configuration.
Abstract: Hematin can substitute for horseradish peroxidase (HRP) as the catalyst in the determination of hydrogen peroxide using phenolic substrates such as p-hydroxyphenylacetate or p-cresol. Although the peroxidatic activity of hematin from bovine blood is not as great as HRP in terms of unit iron content, the activity per unit weight is substantially greater. Hematin is 500 times less expensive than HRP per unit peroxidatic activity. In hematin-catalyzed systems, reaction development and fluorescence measurement can both be conducted optimally in the same ammoniacal buffer. Hydroxyalkyl hydroperoxides are rapidly hydrolyzed to H2O2 at this pH and are also determined. On the other hand, for methyl hydroperoxide, hematin exhibits only approximately 10% of the sensitivity exhibited by HRP. Hematin is significantly more stable in solution than HRP. The use of hematin as catalyst and p-cresol as the substrate leads to a particularly inexpensive and sensitive system, permitting a limit of detection (LOD) of 7 nM H2O2 in a flow-injection configuration.
191 citations
TL;DR: The nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential, and viable reaction mechanisms are proposed for both of these chemistries.
Abstract: Hydrogen sulfide evolved from an acidified sample is pre-concentrated by permeation in a stationary alkaline acceptor solution enclosed in a silicone rubber sample loop. Depending on the sample volume pre-concentrated, the applicable analytical range spans low micrograms/L to tens of mg/L for both methods. The methylene blue method is more sensitive by a factor of approximately 30 and actually permits practical determinations in the sub-micrograms/L levels. The limit of detection (LOD) for the nitroprusside method ranges from 20 micrograms/L for a 20 microL sample by conventional flow-injection determination (no membrane, throughput 30 samples/h) to less than 2 micrograms/L for 12 mL sample pre-concentrated in the membrane system (throughput 5 samples/h). The membrane is highly resistant to fouling and permits analysis of untreated wastewater samples bearing suspended solids, oil, grease, etc. without any pretreatment. No significant interference is observed with either chemistry. Although the nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential. Viable reaction mechanisms are proposed for both of these chemistries.
118 citations
TL;DR: In this article, a 75μm bore fused-silica capillary is used as the pumping mechanism for flow-injection analysis (FIA) and colorimetric detection is performed by an optical absorbance detector using the diameter of the capillary as the optical path.
60 citations
TL;DR: In this article, a tubular membrane is interposed in the separation capillary in capillary electrophoretic separation systems, where a jacket is built outside the membrane, and the sample is introduced by diffusion/permeation through the membrane.
Abstract: Small lengths of narrow-bore tubular membranes can be interposed in the separation capillary in capillary electrophoretic separation systems. These membrane segments can be used as sampling interfaces; a jacket is built outside the membrane, and the sample is introduced by diffusion/permeation through the membrane. Various examples are shown; the determination of gaseous samples through a porous membrane, the determination of ionizable/nonionic solutes by permeation through a silicone rubber membrane, and the separation of low MW constituents in blood plasma by transport through a dialysis membrane. In the first two cases, significant preconcentration is possible, thus permitting attractive detection limits. 23 refs., 10 figs., 2 tabs.
52 citations
TL;DR: With immobilized adsorbents on conduit walls for preconcentration, a limit of detection of < 10(-7)M tetrabutylammonium ion can be obtained with bromothymol blue as the ion-pairing agent.
25 citations
TL;DR: In this paper, an ammoniacal solution of a peroxidase-like catalyst, hematin, was pumped through a porous hydrophob membrane reactor that allowed the introduction of a substrate, p-cresol.
22 citations
TL;DR: In this paper, hydrogen cyanide at low ppbv levels is determined in the presence of several thousand ppmv H 2 S. The gases diffuse through a porous polyvinylidene difluoride (PVDF) tubular membrane into an NaOH absorber; the pH is then adjusted to 95-10, and the liberated HCN is selectively permeated across a tubular silicone rubber membrane into a NaOH absorber.
Abstract: Hydrogen cyanide at low ppbv levels is determined in the presence of several thousand ppmv H 2 S The gases diffuse through a porous poly(vinylidene difluoride) (PVDF) tubular membrane into an NaOH absorber; the pH is then adjusted to 95-10, and the liberated HCN is selectively permeated across a tubular silicone rubber membrane into an NaOH absorber A limit of detection (LOD) of 35 ppbv HCN is attainable with a preconcentration time of 10 min (throughput rate of 5 samples h -1 ) and spectrophotometric determination of cyanide by the Kο#79nlg reaction with sodium isonicotinate and 3-methyl-1-phenyl-2-pyrazolin-5-one
20 citations
TL;DR: Thin film perfluorosulfonate ionomer sensors overcoated with cellulose triacetate, polyvinyl alcohol (PVA)-H 3 -PO 4 , or PVA-PFSI-H 3 PO 4 composite films operated in a pulsed voltammetric mode are described.
Abstract: Thin film perfluorosulfonate ionomer (PFSI) sensors overcoated with cellulose triacetate, polyvinyl alcohol (PVA)-H 3 -PO 4 , or PVA-PFSI-H 3 PO 4 composite films operated in a pulsed voltammetric mode are described
11 citations
TL;DR: The feasibility of determining aqueous ozone by chemiluminescence flow-injection analysis (CL-FIA) was studied for applications in potable water treatment and significant discrimination against the interferents is possible by taking advantage of the much faster kinetics of the CL reaction with ozone.
9 citations
01 Jan 1992
1 citations