Showing papers by "Purnendu K. Dasgupta published in 1987"

Fluorescence Properties of Metal Complexes of 8-Hydroxyquinoline-5-sulfonic Acid and Chromatographic Applications

Abstract: Seventy-eight metal species are examined for fluorescence properties of their chelates with 8-hydroxyquinoline-5-sutfonic acid (HQS); 42 of these fluoresce, many intensely. The optimum pH, determined by ligand ionization vs. hydroxo compiex formation, iles between 5 and 8. Cadmlum forms the most fluorescent complex In a purely aqueous solution. Fluorescence Is enhanced for many metals in surfactant (hexadecyltrlmethyiammonlum ion, HTA') containing media and in a water:dimethytformamide solvent. A number of metal ions quench the fluorescence of other metal-HQS chelates, Fe(II1) being by far the most effective, and such quenching is accentuated in media contalnlng HTA'. The fluorescence propertles can be exploited by introducing the ligand through a postcolumn reactor or by Incorporating it in the eluent in a chromatographic system. Subpicomole detection limits are attainable for Cd, Mg, and Zn.

Fast fluorometric flow injection analysis of formaldehyde in atmospheric water.

Abstract: Formaldehyde can be determined in aqueous solution at a rate of 45 samples/h with a small sample requirement (100 ..mu..L). The fluorescence of 3,5-diacetyl-1,4-dihydrolutidine formed upon reaction of formaldehyde with ammonium acetate and 2,4-pentanedione (25 s, 95 /sup 0/C) is monitored with a filter fluorometer. The detection limit is 0.1 ..mu..M (3 ..mu..g/L) or 10 pmol of HCHO. The response is linear up to 3.3 ..mu..M (100 ..mu..g/L), the departure from linearity at 0.33 mM is 21%, but high levels are satisfactorily determined with a second-order calibration equation. Interference from S(IV) has been investigated in detail and completely eliminated by addition of H/sub 2/O/sub 2/ before rendering the sample alkaline. There are no effects from commonly occurring metal ions and anions; the method is very selective to formaldehyde compared to other carbonyl compounds. A S(IV)-containing preservative has been formulated for the stabilization of low concentrations of HCHO. Results are presented for fogwater samples. 8 figures, 41 references.

Gradient anion chromatography with hydroxide and carbonate eluents using simultaneous conductivity and pH detection

Abstract: High exchange capacity membrane suppressors make gradient anion chromatography practical, with submicromolar detection limits attainable for a number of common anions when a data acquisition system is used to store a blank run and perform background subtraction. With hydroxide eluents, pH measurement yields attractive detection limits. Postsuppressors, based on a porous polypropylene tubular membrane as is, or coated with silicone rubber, permit acceptable performance with the more commonly used carbonate-based eluents. For isocratic elution with hydroxide eluents, direct potentiometric pH detection allows limits of detection only slightly worse than conductometry and is adequate for most purposes.

Performance of annular membrane and screen-tee reactors for postcolumn-reaction detection of metal ions separated by liquid chromatography

Abstract: The experimental factors that contribute to base line noise in the postcolumn-reaction detection of metal ions eluted from high-performance dynamic ion exchangers have been evaluated and compared for a screen-tee reactor (approx. 1 ..mu..L internal volume) and three annular membrane reactions having internal volumes of 1.5, 5.3, and 9.6 ..mu..L. Measurements of mixing homogeneity, performed with pulseless gas-pressure pumping, showed that both reactor designs gave a mixing homogeneity that was 99.983% of that theoretically possible (perfect mixing) for two solutions differing in absorbance by 2.38 units. For normal operation with high-performance reciprocating pumps for eluent delivery, pump pulsations were responsible for 90-100% of the observed peak-to-peak noise. Column efficiency measurements with a series of lanthanide metal ions gave similar curves for both designs (HETP values of 0.01-0.04 mm). Both reactors gave reproducible peak areas, had good peak shapes, and operated reliably. With the membrane reactors some leakage of eluent into the reagent solution occurred at high eluent or reagent flow rates, but this was not a problem for normal operating conditions.

A Diffusion Scrubber for the Collection of Gaseous Nitric Acid

Abstract: A diffusion denuder with a thin anion exchanger membrane tube as the collecting element and with a scrubber solution flowing in a narrow annular gap outside the membrane is described. The use of this device with a dilute sulfate-sulfamic acid solution as scrubber has been exploited for collecting nitric acid. The method is essentially free from interference due to NO2, and response characteristics are described for a continuous flow application. Direct UV detection, used to demonstrate response characteristics in the continuous monitoring mode, is not sufficiently sensitive for the measurement of low levels of ambient gaseous HNO3.

Metal ion chromatography with fluorescence detection

Abstract: Nonpolar, agglomerated anion exchanger, and surface-sulfonated cation exchanger stationary phases have been used in conjunction with 8-hydroxyquinoline-5-sulfonic acid (HQS) in the eluent or as a postcolumn reagent for the separation and detection of a number of metals that form fluorescent HQS complexes. Several metals, notably those classified as transition metals, form nonfluorescent HQS chelates and quenches the fluorescence of other metal-HQS metal chelates. Such transition metals have been detected by introducing the fluorescent Al-HQS chelate postcolumn. Cation exchange stationary phases are the most useful for chromatographic applications involving HQS and are able to provide a variety of useful separations by tailoring elution conditions. Although not sensitive to Ba, the approach may be particularly good for the determination of the other alkaline earth metals. Fluorescence quenching resulting from Fe and Ni leaching from stainless steel chromatographic systems present a problem for tra...

Optical cells with partially reflecting windows as nonlinear absorbance amplifiers

Abstract: An etalon, where the dielectric spacer is a weakly absorbing solution, forms a nonlinear absorbance amplifier. The observed net absorbance is equal to -log (10/sup -3A/4/(1 -R/sub w/)/(1 - 10/sup -A/2/R/sub w/)) where R/sub w/ is the reflectance of the windows and A is the absorbance of the same solution in a conventional cell. Reasonable agreement between theory and experiment is observed for a coherent source. For conventional sources, the observed amplification factor is much higher due to beam divergence, multipath effect, and multiple beam interference.

High sensitivity optical detection methods in hydroxide eluent suppressed anion chromatography via postsuppression ion exchange

Abstract: Detection by post suppression ion exchange, as an adjunct to suppressed hydroxide eluent ion chromatography, involves exchange of eluting sample anion or concurrently present H/sup +/ for a fluorescent/optically absorbing anion or cation such as anthranilate or Ce/sup 3 +/. Membrane-based post suppression devices permit reliable continuous operation, and detection limits can be better than those attainable by conductivity detection. The anion exchange membrane-anthranilate system also yields excellent detection limits by UV absorption except that membrane degradation is a problem. The ion exchange at the membrane interface is not an equilibrium process. The dependence of the membrane response on an external high frequency electrical field suggests that the transport of the ions through the membrane is not a rate-determining factor.

Positive-signal indirect fluorometric detection in ion chromatography

Abstract: Possibilite d'une detection fluorimetrique indirecte pour des concentrations en ions eluants se situant dans la region d'auto-extinction

Preventing undissolved alloying ingredient from entering continuous casting mold

Abstract: Molten steel containing an undissolved alloying ingredient denser than molten steel (e.g. Pb and/or Bi) flows from a tundish to a continuous casting mold. Various expedients are employed to prevent large globules of undissolved alloying ingredient from flowing out of the tundish into the mold. Another expedient prevents large quantities of undissolved alloying ingredient from accumulating on the bottom of the tundish.

Application Of Continuous Liquid Phase Fluorescence Analysis For The Selective Determination Of Gases

Abstract: A porous membrane "Diffusion Scrubber" represents an ideal interface between trace atmospheric gases of interest and sensitive fluorescence-based continuous liquid phase analysis methods for the corresponding analytes. Analytical methods capable of determining low to sub-parts-per-billion levels of hydrogen peroxide, sulfur dioxide, ammonia and formaldehyde on a continuous basis are described.