Kavita Agrawal

Bare silica nanoparticles as concentrating and affinity probes for rapid analysis of aminothiols, lysozyme and peptide mixtures using atmospheric-pressure matrix-assisted laser desorption/ionization ion trap and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The analysis of peptide mixtures from urine and plasma samples using bare (uncapped) SiO2 nanoparticles (NPs) with atmospheric-pressure matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI-MS) has been reported. The method was based on the adsorption of positively charged peptides on the surface of negatively charged SiO2 NPs through the electrostatic force of attraction. The adsorption on the surface of SiO2 NPs caused enhancement of ionization efficiency of analytes and subsequently increased the signal intensity of peptides. Maximum signal intensity was obtained at optimized concentration of SiO2 NPs and pH of the aqueous solution. The limits of detection (LODs) obtained for different peptides in deionized water with and without using SiO2 NPs were in the range 4.7-360 nM and 0.1-18.0 microM, respectively. The sensitivity of the proposed method was 21-53-fold better than conventional use of AP-MALDI-MS. In addition, linearity in the range 9.5-95 nM was obtained for the peptide angiotensin-II in deionized water with a correlation of estimation of 0.992 using an internal standard. The proposed method provided a simple way to facilitate the ionization of peptides, reduce sample complexity and increase the tolerance to salts and surfactants in the analysis of biological samples. The applicability of the present method was also demonstrated in the real-world sample analysis of aminothiols and lysozyme using MALDI-time-of-flight (TOF)-MS.

Trace level determination of molybdenum in environmental and biological samples using surfactant-mediated liquid-liquid extraction.

A novel and sensitive spectrophotometric method for the determination of molybdenum at trace levels in environmental and biological samples is proposed. The method is based on the reaction of Mo (V) with thiocyanate (SCN(-)) and methyltrioctyl ammonium chloride (MTOAC) in acidic medium. The red colored complex of molybdenum is extracted with N-phenylbenzimidoyl thiourea (PBITU) in 1-pentanol for its determination by spectrophotometry. The sensitivity of the present method is higher than other conventional thiocyanate method, due to the use of MTOAC in liquid-liquid extraction. The value of molar absorptivity of the complex with respect to molybdenum is 7.6x10(4)Lmol(-1)cm(-1) at 470nm. The limit of detection of the metal is 5ngmL(-1). The system obeys Beers law between 20 and 1000ngmL(-1) with slope, intercept and correlation coefficient values of 0.81, 2.5x10(-3) and +0.999, respectively. Most of the metal ions tested did not interfere in the determination of molybdenum. The proposed method has been successfully applied for the determination of the molybdenum in environmental and biological samples.

Development of surfactant assisted spectrophotometric method for determination of selenium in waste water samples.

A new, simple and highly selective method for spectrophotometric determination of selenium in waste water samples is described. Selenium(IV) oxidizes I(-) ions into I(2) which subsequently reacts with excess of I(-) ion in the acidic media to give tri-iodide ions (I(3)(-)), and it further reacts with cetylpyridinium cation (CP(+)) to give a violet colored species. The value of molar absorptivity of the ion-associate species in terms of selenium is 1.80 x 10(4) L mol(-1)cm(-1) at lambda(max) 510 nm. The detection limit of the method is 10 ng mL(-1) Se. The calibration curve is linear over 50-1000 ng mL(-1) Se with slope, intercept and co-relation coefficient of 0.23, -4.0 x 10(-4) and +0.99, respectively. None of the tested diverse ions interfered in the present method. The method has been tested for the determination of selenium in waste water samples.

Reverse micellar microextraction for rapid analysis of thiol‐containing peptides and amino acids by atmospheric‐pressure matrix‐assisted laser desorption/ionization ion trap and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Simple, rapid and inexpensive one-step reverse micellar microextraction (RMME) procedures were combined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) for the determination of thiol-containing peptides and amino acids. In this investigation, a thiol-containing peptide (HW6) was chosen as model compound to understand the mechanism of RMME. The electrostatic interactions between the thiol-containing peptide and reverse micelles were proposed to be reason for the transfer of analytes from the aqueous phase to the organic phase. Reverse micelles were formed by the cationic surfactant, methyltrioctylammonium chloride (MTOAC). The best extraction efficiency of HW6 was obtained under the following conditions: pH 11.0, ionic strength 5.0 mM of KCl and micelle concentration 7.0 mM of MTOAC. The limits of detection (LODs) obtained for HW6 in water, urine and plasma samples were 0.15, 0.19 and 0.28 microM, respectively, with relative standard deviation (RSD) values in the range +/-8.8-10.5%. The sensitivity obtained in water by the present method was 45-fold higher than that of the conventional use of atmospheric-pressure (AP)-MALDI MS. Furthermore, the applicability of the proposed approach was extended for the determination of thiol-containing amino acids in sample solutions by using MALDI time-of-flight (TOF) MS.

On-site determination of tin in geological and water samples using novel organic reagent with iodide

A new, simple and sensitive method for spectrophotometric determination of tin (IV) with iodide and amide is described. The Sn(IV)-I(-) complex is extracted with chloroform solution of amide (N-phenylacetamide, N-alkylacetamide, alkyl=butyl, phenyl, hexyl and octyl group) in the strong sulphuric acid solution. Among five amides studied, N-octylacetamide (OAA) has been selected as it yielded best sensitivity. The apparent (at twofold preconcentration) molar absorptivity with respect to tin is (2.40)x10(5)Lmol(-1)cm(-1) at lambda(max), 410nm. The detection limit of the method is 4microgL(-1) Sn. The method is free from interferences of common ions that are normally associated with Sn. The method is highly sensitive and found to be applicable for the rapid determination of tin in water samples at micro-gram levels.

Flow‐Injection Analysis Spectrophotometric Determination of Bismuth in Environmental and Pharmaceutical Samples

Abstract A new, simple, rapid, selective, and sensitive flow‐injection analysis (FIA) method for the spectrophotometric determination of Bi is described. It is based on reaction of Bi (III) with I− ions in the presence of cationic surfactants (CS), i.e., cetylpyridinium chloride, cetyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, dodecyltrimethylammonium bromide in sulfuric media to give a violet‐colored complex. The apparent value of molar absorpitivity of the complex in the terms of Bi with four CSs lie in the range of (1.00–1.20) × 104 L mol−1 cm−1 at λmax 490 nm. Among them, the most sensitive CSs, i.e., cetylpyridinium chloride (CPC) has been selected for the detailed studies. The detection limit (causing absorbance >3 sec) of the method is 65 µg L−1 Bi. The sample throughput of the method is >120 samples hr−1. The effect of diverse ions and surfactants in the FIA determination of Bi is examined. The composition of the complex is discussed. The analytical and FIA variables in the determination of Bi are optimized. The method has been applied for analysis of Bi in the environmental and pharmaceutical materials.