J. Amador-Hernández

Partial least squares regression for problem solving in precious metal analysis by laser induced breakdown spectrometry

The application of laser induced breakdown spectrometry for the quantitative determination of gold and silver in Au–Ag–Cu alloys is proposed. Laser induced plasma emission spectra in the ultraviolet region were studied in order to characterize the spectral information from time-integrated data. The multivariate calibration method known as partial least squares regression type 1 was used for calibration and prediction purposes. Satisfactory results were obtained for the determination of gold and silver without temporal resolution strategies. Since the employment of this chemometric algorithm was a good alternative for simplification of the experimental setup, a rapid, simple and low cost method is thus proposed for the determination of noble metals in jewelry pieces.

On-line detection for supercritical-fluid extraction

An overview of the direct coupling of supercritical-fluid extraction (SFE) to distinct detection is presented. The versatile construction of this kind of hybrid analytical instrumentation is manifested through the discussion of several interface prototypes, whose characteristics satisfy the requirements of both the SF extractor and detector. The application of several experimental strategies during the whole analytical process are proposed for the successful quantification of the leaching yield. Typical examples of SFE with on-line detection in several fields of analysis are presented, considering of special interest the information provided by the molecular and atomic techniques used. Finally, the real analytical capabilities of the automation of sample handling by SFE-continuous detection are also discussed.

Pervaporation: a useful tool in food analysis

Abstract An overview of applications of analytical pervaporation in food analysis is presented. Various designs of both the analytical pervaporation module and the continuous manifolds utilised are discussed in order to show the versatility of this non-chromatographic continuous separation technique for different challenges encountered in the automation of the overall analytical processes. Examples of the on-line analysis of liquid, semi-solid and solid samples in food and beverage industries are detailed. Finally, the potential of pervaporation as an alternative to commonly used gas–liquid separation techniques is also discussed.

Near infrared thermal lens spectrometry for the real-time monitoring of supercritical fluid extraction

A commercially available supercritical fluid extractor provided with carbon dioxide was coupled to a dual-beam thermal lens spectrometer with a pumpprobe coaxial configuration, pumped by a pulsed Nd-YAG laser operating at the fundamental wavelength of 1064 nm. As a preliminary step, several compounds were studied in batch regime using carbon tetrachloride as solvent, in order to observe the influence of overtones and combinations involving distinct chemical bonds on thermal lens spectrometry (TLS). Several factors related with supercritical fluid extraction (SFE) under hydrodynamic conditions were studied in order to establish their influence both in the extraction yield and thermal lens signal magnitude obtained. The advantages and limitations of the hyphenated SFE-TLS technique proposed are discussed, and the possibility of on-line detection in SFE with a pulse thermal lens spectrometer was demonstrated.

Pulse Thermal Lens Spectrometry of beta-Carotene in Flow Systems at Atmospheric- and High-Pressure Conditions

A dual-laser thermal lens spectrometer with a pulse pump-probe coaxial configuration was constructed, optimized, and used to study the influence of flow rate, cell design, nature of the solvent, photostability of the chromophore, and pressure up to 80 atm. β-carotene solutions in 2-propanol, n-hexane, and carbon tetrachloride were pumped through a quartz cell (10 mm pathlength, 30 μL internal volume) and a stainless steel cell (50 mm pathlength, 350 μL internal volume). With β-carotene, flow produces a relative thermal lens spectrometry (TLS) signal magnitude increase owing to replacement of photobleached analyte in the beam region. The effects of pressure in the different solvents are compared and discussed; the relative TLS signal magnitude decreased when pressure increased, but less in carbon tetrachloride than in the other solvents. Limit of detection for β-carotene in carbon tetrachloride at 0.4 mL min-1 and 1 atm were 2 × 10-5 absorbance units.