Identification of an artifact in the mass spectrometry of proteins derivatized with iodoacetamide

Derivatization of cysteinyl residues is often used to prevent the formation of disulfide bonds during protein isolation and analysis. The most commonly used reagents are iodoacetic acid and iodoacetamide, which increase the molecular mass of the protein by 58 or 57 Da, respectively, for each derivatized cysteine. A possible side reaction is derivatization of methionine. In our analysis of derivatized human lens alphaA-crystallins, we found an apparent molecular mass 48 Da lower than the mass expected for alphaA-crystallin with the cysteines carboxyamidomethylated. Analysis of a tryptic digest of this protein showed that both cysteines and one methionine had been derivatized. Peaks indicating a molecular mass 48 Da less than expected for the protein with only cysteines derivatized were attributed to fragmentation of the derivatized methionine through collision-induced dissociation in the electrospray ionization source. An awareness of this artifact is important to investigators searching for proteins and their modified forms in complex mixtures.     

A general approach for the quantitative analysis of bisphosphonates in human serum and urine by high-performance liquid chromatography/tandem mass spectrometry

Bisphosphonates are extremely hydrophilic and structurally similar to many endogenous phosphorylated compounds, making their selective extraction from serum or urine very challenging. Many bisphosphonates lack strong chromophores for sensitive UV or fluorescence detection. We report here the first general approach to enable sensitive and selective quantitation of N-containing bisphosphonates by liquid chromatography/tandem mass spectrometry (LC/MS/MS) following derivatization with diazomethane. The novelty of the strategy lies in performing the derivatization on silica-based anion-exchange sorbents as an integrated step in the sample purification by solid-phase extraction (SPE). The 'on-cartridge' reaction with diazomethane not only led to higher efficiency of derivatization, but also enabled a more discriminatory recovery of the drug's derivatives. The derivatized bisphosphonates demonstrated improved chromatographic separation and increased sensitivity of the detection. The general applicability of the approach was demonstrated by validation of bioanalytical methods for risedronate and alendronate in human serum and urine. Sensitivity was achieved at the pg/mL level with merely 100-200 microL of sample.     

Quantifying uncertainty in the measurement of arsenic in suspended particulate matter by Atomic Absorption Spectrometry with hydride generator

Arsenic is the toxic element, which creates several problems in human being specially when inhaled through air. So the accurate and precise measurement of arsenic in suspended particulate matter (SPM) is of prime importance as it gives information about the level of toxicity in the environment, and preventive measures could be taken in the effective areas. Quality assurance is equally important in the measurement of arsenic in SPM samples before making any decision. The quality and reliability of the data of such volatile elements depends upon the measurement of uncertainty of each step involved from sampling to analysis. The analytical results quantifying uncertainty gives a measure of the confidence level of the concerned laboratory. So the main objective of this study was to determine arsenic content in SPM samples with uncertainty budget and to find out various potential sources of uncertainty, which affects the results. Keeping these facts, we have selected seven diverse sites of Delhi (National Capital of India) for quantification of arsenic content in SPM samples with uncertainty budget following sampling by HVS to analysis by Atomic Absorption Spectrometer-Hydride Generator (AAS-HG). In the measurement of arsenic in SPM samples so many steps are involved from sampling to final result and we have considered various potential sources of uncertainties. The calculation of uncertainty is based on ISO/IEC17025: 2005 document and EURACHEM guideline. It has been found that the final results mostly depend on the uncertainty in measurement mainly due to repeatability, final volume prepared for analysis, weighing balance and sampling by HVS. After the analysis of data of seven diverse sites of Delhi, it has been concluded that during the period from 31^st Jan. 2008 to 7^th Feb. 2008 the arsenic concentration varies from 1.44 ± 0.25 to 5.58 ± 0.55 ng/m³ with 95% confidence level (k = 2).     

The activation characteristics of the decomposition of H<Subscript>2</Subscript>O<Subscript>2</Subscript> on palladium-carbon catalysts

The kinetics of catalytic decomposition of H₂O₂ on palladium-carbon catalysts with various deposited metal distributions in carrier (active carbon) porous granules was studied. The activation parameters (E _a and A ₀) of the process were calculated by the Arrhenius equation. A determining factor for the catalytic process was found to be the entropy factor (A ₀), which characterized the formation and dissociation of activated transition complexes. A quantum-chemical study of the electronic structure of palladium-carbon catalysts showed the occurrence of electron density transfer from the carbon matrix to metal clusters and collectivization of their electronic systems. This increased the donor-acceptor ability of the synthesized materials and, as a consequence, their catalytic activity.     

Potentiometric Study of Oxidized Coals in Aqueous Solutions of Surface-Inactive Electrolytes

Stationary electrode potentials of oxidized synthetic coals of the SCN type are determined in aqueous solutions. The contributions of redox reactions with participation of the surface oxygen-containing functional groups and the potential of unoxidized areas of the coal surface to the total potential of oxidized coals in aerated solutions are studied. The potentials of oxidized carbons in deoxygenated solutions are also measured.     

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC₈) and of the cobalt octanoate (CoC₈). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained.