Time-of-flight-secondary ion mass spectrometry and cyclic voltammetry studies of self-assembly of dodecanethiol on a nanoporous gold surface.

Preparation of a nanoporous gold surface by dealloying (etching) of a 585 gold plate (58.5% Au, 30% Ag, and 11.5% non-noble metals) was studied by applying acidic and thermal treatment of the gold plate. The gold plate surface was studied before and after the etching process using different analytical techniques like field emission scanning electron microscope (FE-SEM) with an energy dispersive X-ray spectroscopy analyzer (EDX), cyclic voltammetry (CV), and time-of-flight-secondary ion mass spectrometry (TOF-SIMS). CV analysis of the gold surface has shown that overnight etching with warm nitric acid increases the surface area 20 times higher than before etching. FE-SEM analysis has shown that a nanoporous gold surface with pore diameter ≤100 nm was obtained. SIMS depth profile analysis and EDX analysis have shown that the nanoporous gold surface was obtained as a result of removing the silver and copper from the first layers of the plate. The nanoporous gold surface was used as a substrate for self-assembly of dodecanethiol and has shown a higher extraction efficiency than the unetched gold alloy.

Development of a new porous gold SPME fiber for selective and efficient extraction of dodecanethiol followed by GC-MS analysis.

The efficiency of a porous gold fiber used for solid-phase microextraction (PG-SPME) was investigated for the extraction of dodecanethiol out of ethanolic solution. A commercially available standard SPME (polydimethylsiloxane, carboxen, divinylbenzene-PDMS-Carb-DVB) was used as a reference to compare the extraction efficiency and selectivity of dodecanethiol with the PG-SPME fiber. The porous gold SPME fiber allowed the analysis of self-assembled monolayers on gold by gas chromatography-mass spectrometry (GC-MS). The PG-SPME fiber showed a five times higher peak area for dodecanethiol in GC-MS compared to the standard PDMS-Carb-DVB fiber.

Determination of sulfonamides and trimethoprim using high temperature HPLC with simultaneous temperature and solvent gradient.

A fast HPLC method for the analysis of eight selected sulfonamides (SA) and trimethoprim has been developed with the use of high temperature HPLC. The separation could be achieved in less than 1.5 min on a 50 mm sub 2 microm column with simultaneous solvent and temperature gradient programming. Due to the lower viscosity of the mobile phase and the increased mass transfer at higher temperatures, the separation could be performed on a conventional HPLC system obtaining peak widths at half height between 0.6 and 1.3 s.

Influence of the stationary phase on the stability of thalidomide and comparison of different methods for the quantification of thalidomide in tablets using high-temperature liquid chromatography.

In this paper, three different HPLC methods for the quantification of thalidomide in tablets were developed and compared. The comparison of a conventional method at 30 degrees C with two high-temperature methods at 180 degrees C showed equal results. Using high-temperature HPLC (HT-HPLC), faster analysis times could be achieved. We have also focused on analyte stability and could show that the stationary phase has a pronounced effect on the on-column degradation of thalidomide at high temperatures. Virtually no degradation occurs if a polystyrene divinylbenzene column is used, whereas thalidomide is completely degraded at 180 degrees C when a carbon clad zirconium dioxide column is used.

Direct on-line continuous supercritical fluid extraction and HPLC of aqueous pyrethrins solutions.

A new method, employing supercritical fluid extraction (SFE) connected on-line with high-performance liquid chromatography, was developed for the determination of pyrethrins and piperonyl butoxide in aqueous solutions. The principle of the laboratory-made device for SFE is based on the low mutual solubility of water and supercritical (liquid) CO2. This device works in continuous mode that offers extraction of unlimited sample volumes. Different extraction temperatures and pressures were tested to find optimum extraction conditions. The addition of organic modifier and inorganic salt to the water sample to increase extraction recovery was investigated. The method was evaluated, and it was applied for the extraction of aqueous samples spiked with commercial insecticides. The working concentration range of the method was from the limit of quantification (0.1 microg L(-1)) to the solubility of the analytes in water.