Current Analytical Chemistry - Volume 5, Issue 3, 2009

An indirect flow injection spectrophotometric procedure for the determination of ranitidine in pharmaceutical formulations is proposed. The method was based on the oxidation of the ranitidine with cerium(IV) in acidic medium and subsequent determination of cerium(IV) excess by reaction with ferroin which was monitored spectrophotometrically at 500 nm. The linearity of the analytical curve for ranitidine ranged from 2.5 x 10-4 to 1.25 x 10-3 mol L-1. The detection limit of 1.6 x 10-6 mol L-1 and recoveries between 96.6 and 103 % were obtained. The sampling rate of 60 determinations per hour and the RSD smaller than 0.3% for 7.1 x 10-4 mol L-1 ranitidine were also obtained. The method was applied with success in the determination of ranitidine in several commercial formulations.

Sample treatment/preparation procedures using octadecylsilane as common phase for solid-phase extraction (SPE) and solid-phase microextraction (SPME) were compared for the analysis of the pesticides pyrimethanil, kresoximmethyl and tebufenpyrad in water samples. SPE and SPME were followed by gas chromatography-mass spectrometry (GC-MS). SPE require 500 mL of sample and leads to a limit of detection in the range 0.005-0.02 ng/mL. SPME requires only 4.0 mL of sample and provides a limit of detection in the range 0.004-0.03 ng/mL. No significant difference between pesticides found in spiked samples using SPE and SPME were obtained. The main advantages of SPE were better precision and ruggedness. The main advantage of SPME method is that the cost of octadecylsilane fiber is negligible compared to octadecylsilane 500 mg cartridges or SPME commercial fibers.

Carbohydrates exhibit many physiologically and pharmacologically important activities, yet their complicated structure and sequence pose major analytical challenges. Although their structural complexity makes analysis of carbohydrate difficult, mass spectrometry (MS) with high sensitivity, resolution and accuracy has become a vital tool in many applications related to analysis of carbohydrates or oligosaccharides. This application is essentially based on soft ionization technique which facilitates the ionization and vaporization of large, polar and thermally labile biomolecules. Electrospray- ionization (ESI), one of the soft ionization technique, tandem MS has been used in the sequencing of peptides, proteins, lipids, nucleic acids and more recently carbohydrates. The development of the ESI and tandem MS has begun to make carbohydrate analysis more routine. This review will focus on the application of the ESI tandem MS for the sequence analysis of native oligosaccharides, including neutral saccharides with multiple linkages, and the uronic acid polymers, alginate and glycosaminoglycans structures containing epimers.

This paper describes a method for voriconazole assay in pharmaceuticals by using differential pulse polarography (DPP). The voriconazole standard was obtained from pharmaceutical formulations and its purity determined by LC/UV, LC/ESI/MS and DSC analyses. In the DPP analysis a well defined peak (-1.01 V, vs. Ag/AgCl), useful for an accurate and precise assay, was obtained using a 0.01 M KH2PO4 water solution (pH 4.5) as supporting electrolyte. The analytical procedure was successfully applied to the voriconazole determination in tablets and injectables.

The electrochemical behavior of Zinc(II)-furdap amide complex has been investigated by the use of several electrochemical methods in DMSO on platinum electrode. Both the ligand and the complex gave one electron transfer reduction. Although there was no oxidation peak observed corresponding to the reduction of ligand, there was a corresponding oxidation peak appeared for the complex. The number of electrons transferred was calculated as 1 by the use of bulk electrolysis, rotating disc electrodes employing Koutecky -Levich equation. The reversibility tests revealed that the reaction followed a quasi reversible mechanism. The mechanism was also confirmed by simulation studies. ks and α values were found to be 1.0x10^-7 cm s^-1 and 0.4, respectively. The diffusion coefficient (D) was found as 6.93 x10^-5 cm² s^-1 by the use of Cottrell slope obtained from chronoamperometry experiments and ultra micro disc steady state current (iss).

Supramolecular ionophores have in the few past years gained increasing interest in the field of analytical chemistry because of their large varieties and applications in chemical sensors. Calixarenes are considered an important class of supramolecular compounds used in construction of many electrochemical sensors in the past years. This review discusses the main applications of calixarenes in the assay of pharmaceutical, biological and inorganic compounds using electrochemical sensors from 2001 up-to-date.

The production of volatile organic compounds (VOC) by plants is well known. However, few scientific groups have studied VOC produced by green, brown and red algae. Headspace collection of volatiles and solid phase microextraction, as well as the traditional extraction by hydrodistillation combined with analytical chromatographic techniques (i.e., GC-MS), have significantly improved the investigation of VOC from plants and algae. The major volatile compounds found in seaweeds are hydrocarbons, terpenes, phenols, alcohols, aldehydes, ketones, esters, fatty acids and halogen or sulfur-containing compounds. This article presents an overview of VOC isolated from and identified in marine macro-algae. Focus is given to non-halogenated and non-sulfur volatile compounds, as well as strategies to analyze and identify algal VOC by GC-MS.