Victor I. Grishko

Nondestructive and Nonintrusive Determination of Chemical and Isotopic Purity of Solvents by Near-Infrared Thermal Lens Spectrometry

A novel instrument which is based on the use of the thermal lens effect to facilitate the sensitive measurements of the absorption in the near-infrared region has been developed. In this instrument, the near-IR excitation light was provided by a solid-state, spectra-tunable (from 860 to 1060 nm) titanium:sapphire laser. The heat generated as a consequence of the sample absorption of the excitation beam was monitored in the visible region by a He-Ne laser. The data obtained were analyzed by multivariate calibration methods for the nondestructive, noninvasive determinations of chemical and isotopic impurities in solvents. Water in D2O and in tetrahydrofuran can be detected at levels as low as 0.006 and 0.3% (v/v). The method can also be used for the simultaneous determination of water and DMSO-h6 in DMSO-d6 and CD3OH in CD3OH, CD2HOH, and CDH2OH at levels as low as 10−3% (w/w).

Direct and indirect detection of liquid chromatography by infrared thermal lens spectrometry

Abstract A novel, sensitive and universal detector for liquid chromatography has been developed. This detector is based on the measurement of infrared absorption of effluents by the thermal lens effect. In this instrument, the chromatographic effluent was excited by infrared radiation derived from a solid-state tunable F-center laser. The heat generated as a consequence of the sample absorption of the infrared radiation was measured by a He-Ne monitoring laser whose beam was collinearly overlapped with the excitation infrared beam in the sample. The technique is universal because it can be used for the detection of compounds which have absorption in the infrared region (by direct detection) as well as non-absorbing compounds (by indirect detection). The sensitivity of the technique is directly proportional to the excitation laser power, and with the used of laser power of only 4.5 mW, the technique is at least ten times more sensitive than corresponding absorption detectors. A detection limit of picograms was achieved for phenol and its chloro substituents.

Molecular State and Distribution of Fullerenes Entrapped in Sol-Gel Samples †

A novel synthetic method that can encapsulate fullerene molecules (pure C60, pure C70, or their mixture) over a wide range of concentrations ranging from micromolar to millimolar in hybrid glass by a sol-gel method without any time-consuming, complicated, and unwanted extra steps (e.g., addition of a surfactant or derivatization of the fullerenes) has been successfully developed. The molecular state and distribution of encapsulated fullerene molecules in these sol-gel samples were unequivocally characterized using newly developed multispectral imaging techniques. The high sensitivity (single-pixel resolution) and ability of these instruments to record multispectral images at different spatial resolutions (approximately 10 microm with the macroscopic instrument and approximately 0.8 microm with the microscopic instrument) make them uniquely suited for this task. Specifically, the imaging instruments can be used to simultaneously measure multispectral images of sol-gel-encapsulated C60 and C70 molecules at many different positions within a sol-gel sample in an area either as large as 3 mm x 4 mm (with the macroscopic imaging instrument) or as small as 0.8 microm x 0.8 microm (with the microscopic instrument). The absorption spectrum of the fullerene molecule at each position can then be calculated either by averaging the intensity of a 15 x 15 square of pixels (which corresponds to an area of 3 mm x 4 mm) or from the intensity of a single pixel (i.e., an area of about 0.8 microm x 0.8 microm), respectively. The molecular state and distribution of fullerene molecules within sol-gel samples can then be determined from the calculated spectra. It was found that spectra of encapsulated C60 and C70 measured at five different positions within a sol-gel sample were similar not only to one another but also to spectra measured at six different times during the sol-gel reaction process (from t = 0 to 10 days). Furthermore, these spectra are similar to the corresponding spectra of monomeric C60 or C70 molecules in solution. Similarly, spectra of sol-gel samples containing a mixture of C60 and C70 were found to be the same at five different positions, as well as similar to spectra calculated from an average of the spectra of C60 and C70 either encapsulated in a sol-gel or in solution. It is evident from these results that C60 and C70 molecules do not undergo aggregation upon encapsulation into a sol-gel but rather remain in their monomeric state. Furthermore, entrapped C60 and C70 molecules in their monomeric state were distributed homogeneously throughout the entire sol-gel samples. Such a conclusion can be readily, quickly, and easily obtained, not with traditional spectroscopic techniques based on the use of a single-channel detector (absorption, fluorescence, infrared, Raman) but rather with the newly developed multispectral imaging technique. More importantly, the novel synthetic method reported here makes it possible, for the first time, to homogenously entrap monomeric fullerene molecules (C60, C70, or their mixture) in a sol-gel at various concentrations ranging from as low as 2.2 mM C60 (or 190 microM C70) to as high as 4.2 mM C60 (or 360 microM C70).

Measuring Infrared Absorption in the Visible: Sensitive Determinations of Chemical and Isotopic Purity of Solvents by the Thermal Lens Effect

A new technique has been developed in which the absorption in the infrared region is measured in the visible. This was accomplished by use of the visible (probe) laser to monitor the thermal lens effect that was induced in a sample as a consequence of its absorption of the radiation in the infrared. The sensitivity of the technique is much higher than that of conventional transmission measurements because, in addition to its inherent ultrasensitivity, the infrared absorption is measured in the visible region, which has relatively less noise, and is detected by a phase-lock detecting method. With the use of the partial least-squares method to analyze the data, this technique can be used for the nondestructive, noninvasive, and sensitive determination of the chemical and isotopic purity of samples. Specifically, it is capable of measuring water in D2O and in tetrahydrofuran at levels as low as 3.75 × 10−4 and 1.20 × 10−4% (w/w), respectively.