Terahertz pulsed spectroscopy as a new tool for measuring the structuring effect of solutes on water.

Absorption spectra of aqueous solution of ''chaotropes'' (structure maker) and ''kosmotropes'' (structure breaker) have been recorded in the mid-infrared (MIR) and terahertz (THz) spectral region. A different impact of the two groups of solutes on the absorption spectrum of water was found in the recorded THz spectra. A concentration-dependent increased absorption across the investigated THz spectral region (0.04-2 THz, 1.3-66 cm(-1), respectively) has been recorded for all studied chaotropic solutions, whereas the opposite has been obtained for kosmotrope containing solutions. In the case of ionic solutes a further increase in absorption towards higher frequencies was measured. The distinction between chaotrope and kosmotrope solutes was, as expected, also possible in the MIR spectral region. Depending on the structure-forming effect of the solute the OH stretch vibration of the water (around 3400 cm(-1)) was slightly shifted. A red shift has been observed for solution of kosmotropes, whereas a blue shift was observed in the case of solutions containing chaotropes. Compared to the MIR spectral region the structure influencing effect of solutes can be more efficiently studied in the THz spectral region, which provides information from interactions between neighboring water molecules.

Direct determination of carbon dioxide in aqueous solution using mid-infrared quantum cascade lasers.

A method for the direct determination of carbon dioxide in aqueous solutions using a room-temperature mid-infrared (MIR) quantum cascade laser at 2330 cm(-1) is reported. The absorption values of different carbon dioxide concentrations were measured in a 119 microm CaF2 flow-through cell. An optical system made of parabolic mirrors was used to probe the flow cell and to focus the laser beam on the mercury cadmium telluride (MCT) detector. Aqueous carbon dioxide standards were prepared by feeding different mixtures of gaseous N2 and CO2 through wash bottles at controlled temperature. The concentration of the dissolved CO2 was calculated according to Henry's law, taking into account the temperature and the partial pressure of CO2. The carbon dioxide standards were connected via a selection valve to a peristaltic pump for subsequent, automated measurement in the flow-through cell. A calibration curve was obtained in the range of 0.338 to 1.350 g/L CO2 with a standard deviation of the method sxo equal to 19.4 mg/L CO2. The limit of detection was calculated as three times the baseline noise over time and was determined to be 39 mg/L.

Mid-IR synchrotron radiation for molecular specific detection in microchip-based analysis systems.

Microstructures constructed from SU-8 polymer and produced on CaF(2) base plates have been developed for microchip-based analysis systems used to perform FTIR spectroscopic detection using mid-IR synchrotron radiation. The high brilliance of the synchrotron source enables measurements at spot sizes at the diffraction limit of mid-IR radiation. This corresponds to a spatial resolution of a few micrometers (5-20 microm). These small measurement spots are useful for lab-on-a-chip devices, since their sizes are comparable to those of the structures usually used in these devices. Two different types of microchips are introduced here. The first chip was designed for time-resolved FTIR investigations of chemical reactions in solution. The second chip was designed for chip-based electrophoresis with IR detection on-chip. The results obtained prove the operational functionality of these chips, and indicate the potential of these new devices for further applications in (bio)analytical chemistry.

Speciation of butyltin compounds in marine sediments by preconcentration on C60 and gas chromatography-mass spectrometry.

A new method for the speciation of butyltin compounds by solid phase extraction and direct injection using gas chromatography-mass spectrometry (GC/MS) is described. The compounds were complexed with sodium diethyldithiocarbamate and retained on a C60 sorbent column. The neutral chelates of butyltin compounds were eluted with ethyl acetate containing NaBPr4 as derivatising reagent. The main analytical figures of merit of the proposed method for 10 ml of sample are: linear range 0.2-35 ng/g expressed as Sn; limits of detection, 0.07, 0.09 and 0.10 ng/g as Sn for monobutyltin, dibutyltin and tributyltin, respectively. No interferences from metal ions such as Zn2+, Fe3+, Sb3t, Pb2+, Ni2+ and Mn2+ were observed in the determination of organotin compounds. The validation of method was performed out by the analysis of a standard reference sediment (CRM 462). The method was also applied to the determination of butyltin compounds in marine sediment samples.

Innovations in the speciation of organolead compounds in water: towards a more rational, rapid, and simple analytical process.

Speciation analysis calls for rapid, simple systems for minimizing errors made in the most troublesome of all steps in the analytical process: sample preparation. In this context, continuous-flow systems are of great help. The evolution in the different methodologies enabled solutions to the main shortcomings occurring from the lack of selectivity of using RP-C18 as sorbent material. One solution was a shift to more sensitive and selective, but only partially automated, systems employing C60 fullerene and Grignard's reagent; another was a shift to completely automated systems employing sodium tetrapropylborate; and a final solution was to employ the simplest possible configuration by removing the reagent stream. The analytical methods developed allowed the identification and quantification of different organolead species at the pg/ml levels in rainwater samples, with precision (RSD) of about 5% and recoveries ranging from 92 to 100%.

Comparison of three coupled gas chromatographic detectors (MS, MIP-AES, ICP-TOFMS) for organolead speciation analysis.

An automatic unit for the screening of rainwater is used for the determination of organolead compounds using different detectors coupled to a gas chromatograph. A systematic overview is given of the advantages and disadvantages of several detectors (electron ionization mass spectrometry, EI-MS; microwave induced plasma atomic emission spectrometry, MIP-AES; and inductively coupled plasma time-of-flight mass spectrometry, ICP-TOFMS, for the speciation of organolead compounds on the basis of sensitivity, selectivity and reliability. C60 fullerene and RP-C18 were used as sorbent materials for these compounds. The primary assets of the fullerene sorbent, as compared to C18 sorbent, are high sensitivity and selectivity resulting from efficient adsorption due to large surface area and interstitial volume. Among the detection systems, GC/ ICP-TOFMS is the most sensitive, with absolute detection limits of approximately 15 fg of organolead compounds (as lead) using 5-mL sample volumes. Except for diethyllead, similar sensitivities were obtained by MIP-AES. GC/MS is intrinsically the most specific option, because the species are detected directly from molecular information. The precision is similar for all detectors. The screening of rainwater from different locations showed that samples collected in countries in which leaded gasolines are now banned contain organolead species at concentrations below 2 pg/ mL, levels that can be detected only for sample volumes of 25 mL and using MIP-AES or ICP-TOFMS as detectors, their determination being impossible by GC/MS.