Susana Cabredo

Simultaneous determination of arsenic, antimony, selenium and tin by gas phase molecular absorption spectrometry after two step hydride generation and preconcentration in a cold trap system

A cold trap system for the simultaneous determination of arsenic, antimony, selenium and tin by continuous hydride generation and gas phase molecular absorption spectrometry is described. The hydride generation is carried out in two steps; first, tin hydride is generated at low acidity and second, arsenic, antimony and selenium hydrides are formed at higher acidity. All the hydrides are collected in a liquid nitrogen cryogenic trap and transported to the flow cell of a diode array spectrophotometer, where molecular absorption spectra are obtained in the 190-250 nm range. Five calibration solutions containing arsenic, antimony, selenium and tin are solved using multiple linear regression analysis. Tests are performed in order to extend the same manifold to other hydrides but no signals are obtained for bismuth, cadmium, lead, tellurium and germanium. Under the optimum conditions found and using the wavelengths of maximum sensitivity (190, 198, 220 and 194 nm), the analytical characteristics of each element are calculated. The detection limits are 0.050, 0.020, 0.12 and 1.1 mug ml(-1) and the RSD values are 3.7, 3.1, 3.5 and 3.0% for As, Sb, Se and Sn, respectively. The method is applied to As, Sb, Se and Sn determination in natural spiked water samples.

Bioaerosols chemometric characterization by laser-induced fluorescence: Air sample analysis

A laser-induced fluorescence (LIF) system was optimized using a solution of Micrococcus luteus in ethanol/water 50% (v/v) to obtain spectra in the gas phase of 46 bioaerosols. Experimental designs such as Plackett-Burman and factorial design were applied. The fluorescence spectra were treated chemometrically by principal component analysis, linear discriminant analysis and hierarchical cluster analysis to classify the microorganisms according to family, morphology and gram. The best results were obtained using LDA. The method was applied to air samples and the LIF results allowed to characterize bioaerosols reliability. The robustness of the technique was demonstrated by the identification of many bacteria.

Gas chromatography with UV-vis molecular absorption spectrometry detection: Increasing sensitivity of the determination of alcohols and phenols by derivatization

SummaryA method is proposed for the determination of alcohols and phenols based on their derivatization to benzoates and gas chromatography-gas phase molecular absorption spectrometry. All parameters affecting the derivatization reaction, such as the solvent, basic medium, benzoyl chloride and stirring time, were optimized. Chromatographic and instrumental conditions were also studied. Finally, a calibration study was performed and the results were compared to that obtained by the direct determination of the compounds.

Gas chromatography with UV-vis molecular absorption spectrometry detection : Data acquisition and treatment when using a diode-array spectrophotometer

SummaryThis article describes a theoretical/practical study of the parameters which affect the chromatograms obtained when using a molecular diode-array spectrometer as the detector in gas chromatography. The objective is to offer some rules which permit the identification of the optimum signal/noise relation. To achieve this, we study the effect of the different parameters which affect the noise and how to reduce their impact, as well as alternatives for increasing the signal. All the options tested can be applied by correctly programming the spectrometer with BASIC programs, within reach of any use who has even a small understanding of programming. Finally, we consider the effect that the selection of the acquisition conditions may have on the chromatographic resolution. All the studies are carried out using a mixture of alcohols and phenols.

Heated flow-cell for gas phase UV-visible detector in gas chromatography of polycyclic aromatic hydrocarbons

SummaryA detection system for gas chromatography based on gas-phase, molecular absorption measurements is presented, in which the chromatographic column is directly joined to the spectrophotometer flow cell, without heated transfer lines. To maintain polyciclic aromatic hydrocarbons (PAHs) in the gas phase during detection an aluminium heater was constructed. A mixture of 13 PAHs was then separated and analyzed. Parameters affecting separation (temperature program and carrier gas flow) were studied and a program designed to modify the measurement wavelength during the chromatography. The analytical characteristics of each compound were calculated, obtaining detection limits 0.2–1.5 μg mL−. Given that some compounds overlaped, it was necessary to resolve their peaks mathematicaly. Finally, the method was applied to a certified synthetic mixture, with good results.

Gas-phase molecular absorption spectrometry: Determination of sulphite with diode-array detection

A method is described for determining sulphite by SO2 generation and UV-visible molecular absorption spectrometry with diode-array detection. The molecular absorption maximum of SO2 appears at 198 nm. The parameters affecting generation (particularly those relating to the kinetics of the process) and determination are optimized; under the optimum conditions found, only a 30 s preconcentration time is necessary. The linear response range is between 10 and 1000 μg ml−1 of SO32−, the RSD is 3.5% and the detection limit is 3.2 μg ml−1. The effect of different species on the SO2 signal is also studied. The method is applied to the determination of SO2 in air samples.