Compact, open and general purpose cell of variable effective pathlength: direct absorption measurement of SO(4)(2-) in water.

The use of an optothermal window (OW) was proposed for the direct (no need for sample preparation) spectroscopic, non-destructive measurement of SO(4)(2-) in water at 1078 cm(-1). The presently determined limit of detection (LOD) of 1 mmol/L is comparable to that provided by CO(2) laser photoacoustic spectroscopy, but about one order of magnitude superior to that obtainable by the ATR method.

A novel approach to the distortion assessment of denture impression trays.

A novel method to treat and interpret distortion of denture impression trays has been proposed. When compared with the conventional method this approach, based on the general least squares principle, offers a significant advantage since the displacement for each individual point can be traced providing more profound insight into the character of the overall deformation itself. The method was applied to study dental impression trays manufactured of self-curing acrylic. The results indicate the existence of a large degree of individuality and non-uniform behaviour of a specific tray material. The method developed here can be applied to specimens of any arbitrary size and shape and it is not limited by the number of the reference points.

The optothermal approach to a real time monitoring of glucose content during fermentation by brewers' yeast.

During production of both normal and low-alcohol beers, sugar is fermented to ethanol, carbon dioxide and several flavour products. Tight control of fermentation is necessary in order to keep production costs low, and to prevent formation of excessive ethanol in low-alcohol beer. Several types of control devices based on, e.g., determination of carbon dioxide, ethanol, and extract have been developed so far; the main disadvantage of these devices is their unsuitability for on-line applications. Here, the optothermal window was used in a laboratory experiment as a new sensor for real time monitoring fermentation of glucose by Saccharomyces cerevisiae, and the results were compared to those obtained by conventional techniques.

Ultrasensitive determination of beta-carotene in fish oil-based supplementary drugs by HPLC-TLS.

This research study demonstrates that thermal lens spectrometry (TLS) combined with efficient isocratic HPLC separation provides an excellent analytical means to profile and quantify carotenes in fish body oils and possibly also in vegetable oils. In particular, a highly sensitive, selective, simple and rapid method for the determination of ultratraces of beta-carotene in fish oil-based supplementary drugs has been proposed. The analyte could be determined reliably and precisely in the presence of a complex matrix including other fat-soluble vitamins (A, D and E), polyunsaturated fatty acids, sterols and other pigments by matrix-matched calibration in cod liver oil. The suitability of the method is also evidenced by favourable analytical figures of merit for beta-carotene such as a linearity range of 1-120 ng ml(-1), LOD of 0.58 ng ml(-1), recovery of 101.4+/-3.3% and measurement repeatability of 4.1%.

Ultrasensitive determination of trans-beta-carotene in rat and beef livers by means of high-performance liquid chromatography coupled with thermal lens detection.

Hyphenated high-performance liquid chromatography (HPLC)-thermal lens spectrometry (TLS) was demonstrated as a method capable of selectively profiling carotenoids in animal livers and suitable for ultrasensitive determination of trans-beta-carotene in the same tissues. The new approach, HPLC-TLS, a first choice method when studying the tissues containing minute quantities of trans-beta-carotene such as in the case of rat liver, also proved useful in the analysis of beef liver. Due to high sensitivity of the HPLC-TLS method, there is no need for enrichment of liver extracts; in fact, multifold diluted extracts can be analysed directly which not only preserves carotenoids from structural transformations, but also minimises the risk for contamination of the stationary phase. Furthermore, both the calibration in a matrix-matched medium and standard addition method have thus become unnecessary. Reliable determinations of trans-beta-carotene in rat and beef livers (recoveries 98.0 and 99.8%) were obtained by calibration in the mobile phase within the linearity range 1-130 ng ml(-1). In addition, favourable detection limits (0.39 and 0.49 ng ml(-1)), precision of determination (2.8-7.2%) and the selectivity evidenced in the presence of multifold molar excess of vitamins A and E, cholesterol and lecithin, confirm the suitability of the method. The HPLC-TLS approach can be successfully applied in studies concerned with the biotransformation of beta-carotene which are of both scientific and public health interest.

Gas coupled laser photothermal interferometry for non-destructive and non-contact studies of biological specimens.

Photothermal signals from some biological materials exposed to modulated CO2 laser radiation were detected using the concept of photothermal interferometry. The magnitude and a phase of the signals were found to contain qualitative information about subsurface structural changes and variations of moisture content.

Determination of trans-beta-carotene and other carotenoids in blood plasma using high-performance liquid chromatography and thermal lens detection.

Thermal lens spectrometry (TLS) was applied for the detection of beta-cryptoxanthin, alpha-carotene, trans-beta-carotene, and lycopen in blood plasma. This combined high-performance liquid chromatography-TLS (HPLC-TLS) method was validated by comparison with HPLC-UV-Vis analysis of blood plasma under identical chromatographic conditions and by comparing the results obtained from an independent, standard HPLC procedure for determination of carotenoids in blood plasma samples. The results demonstrated good agreement with the target values for carotenoids in an in-laboratory control sample and confirmed the accuracy of the HPLC-TLS technique. Limits of detection for blood plasma samples were 70 pg/ml for beta-cryptoxanthin, 85 pg/ml for alpha-carotene, 100 pg/ml for trans-beta-carotene, and 120 pg/ml for lycopen. This represents a 100-fold improvement compared to the HPLC analysis with UV-Vis detection.

Photoacoustic characterization of different food samples.

Photoacoustic spectroscopy in the 350-700 nm range proved a useful tool for discriminating between a variety of opaque, light-scattering samples. Spectral features originating from powdered food specimens of different colour and grain size were observed. These results suggest the feasibility of photoacoustics for quality control in the food-processing industry.

Detection of Total Trans Fatty Acids Content in Margarine: An Intercomparison Study of GLC, GLC + TLC, FT-IR, and Optothermal Window (Open Photoacoustic Cell).

Four techniques, i.e., gas-liquid chromatography, gas-liquid chromatography + thin-layer chromatography, and two spectroscopic methods, Fourier transform infrared spectroscopy and optothermal window, a variant of the open photoacoustic cell, were intercompared to determine their potential to detect the total trans fatty acid content in margarine. At the same time, this study represents a first application of the optothermal window technique at long wavelengths (10 µm). The total trans fatty acid data obtained by different methods show good mutual agreement. Besides offering several attractive advantages above conventional methods, the optothermal window also proved suitable for measuring total trans fatty acid content as low as 2%.

Resonant Stark spectrophone as an enhanced trace level ammonia concentration detector: design and performance at CO(2) laser frequencies.

A design of a Stark photoacoustic cell capable of detecting ammonia in ambient air at trace levels is discussed.

Determination of ammonia using carbon dioxide laser photoacoustic spectroscopy compared with conventional spectrophotometry.

The potential of carbon dioxide laser photoacoustic spectroscopy and the traditional Indophenol Blue colorimetric method for detecting gaseous ammonia have been compared. The results obtained with the two independent techniques are comparable in the range of concentrations studied.

Monitoring the polymerization process of acrylic resins.

Four groups of autopolymerizing acrylic resins used for various purposes in current dental practice were investigated by monitoring their temperature changes during the polymerization process. Resins were compared in terms of characteristic parameters (such as the time interval needed to reach mechanical stability and the maximum temperature generated during the polymerization process) and interpretations were made of such temporal temperature profiles.