I. V. Mikheev

Solid Phase-Enhanced Photothermal Lensing with Mesoporous Polymethacrylate Matrices for Optical-Sensing Chemical Analysis

Procedures for the photothermal lens determination of metals and organic compounds, on the basis of solid-phase mesoporous optical-sensing materials (polymethacrylate [PMA]) matrices with immobilized reagents, were developed. These procedures combine (i) selective and efficient preconcentration of trace substances to be analyzed in specially designed and synthesized transparent mesoporous PMA plates; (ii) sensitive determination with the reliable and traceable photometric reactions previously developed for classical spectrophotometry; and (iii) the sensitivity enhancement of photothermal lens detection in polymers, which provides at least a ten-fold increase in sensitivity compared with solutions due to polymer thermo-optical properties (solid phase–enhanced thermal lensing). It is shown that the overall sensitivity of photothermal lens measurements in PMA matrices is two orders higher than photometric absorbance measurements for the same excitation source power, which is in good agreement with the expected theoretical sensitivity. Changes in the preparation of transparent PMA plates and analytical procedures for photothermal measurements compared with spectrophotometry are discussed. PMA matrices modified with various analytical reagents were applied to trace determination of Hg(II), Fe(II), Ag(I), Cu(II), and ascorbic acid, with subnanomolar to nanomolar limits of detection.

Structure and toxicity of aqueous fullerene C60 solutions

In this paper, two types of fullerene C60 solutions are compared with respect to their structural features and toxic properties. The results are discussed in terms of their potential in medical and biological applications. The fullerene cluster state at the nanoscale in these solutions is analyzed by small-angle neutron scattering. Experiments on the cytotoxicity of these systems on Chinese-hamster V-79 cells showed no toxic effects of the solutions.

Quantification of copolymer composition (methyl acrylate and itaconic acid) in polyacrylonitrile carbon-fiber precursors by FTIR-spectroscopy

Conditions for simple and sensitive FTIR quantitative determination of acrylonitrile, methyl acrylate, and itaconic acid in their copolymer films used as precursor products in carbon-fiber manufacturing are proposed. The measurement mode is IR-spectrophotometry (transmission) with internal spectrum normalization using the peak of acrylonitrile at 2242 cm−1 as the main component and the determination of itaconic acid and methyl acrylate by their overlapping carbonyl peaks at 1740–1700 cm−1. The calculations of comonomer concentrations were made using an external-standard method. The LOQs of itaconic acid and methyl acrylate are 0.5 and 2% w/w, respectively. The RSD of measurements is no higher than 7% rel. for methyl acrylate, 8% rel. for itaconic acid, and 1% rel. for acrylonitrile, which was shown by an example of analysis of PAN fiber samples with known concentrations of the components. The procedure was tested with several thermally unprocessed PAN precursor samples.

High-Sensitivity and High-Performance Determination of Trace Aluminum in Water for Pharmaceutical Purposes by Microwave Plasma and Inductively Coupled Plasma–Atomic Emission Spectrometry

ABSTRACT Procedures for the determination of aluminum in water for injections (Aqua ad iniectabilia) and high-purity water (Aqua valde purificata) at a level of several µg L−1 using atomic-emission spectrometry with a novel microwave plasma (MP–AES) and inductively coupled plasma (ICP–AES) are proposed. Regardless of the atomic-emission technique used, the procedure for aluminum needs no sample preparation (acidification only), no preconcentration, shows high sensitivity (limits of detection of 0.4 and 0.7 µg L−1 for ICP–AES and MP–AES with a polymeric inert concentric nebulizer, respectively, and 0.03 µg L−1 for ICP–AES with an ultrasonic nebulizer), high precision (repeatability, relative standard deviation, <5%), and high throughput (25 samples per hour), and is considerably simpler and more expedient from the viewpoint of the analysis cost and time compared with the standard spectrofluorimetric procedure of the US and the European Pharmacopoeia.

Approaches to the determination of C60 and C70 fullerene and their mixtures in aqueous and organic solutions

The solvent-exchange process from toluene was used for preparing aqueous dispersions of C60 and C70 without preconcentration with final concentrations of 180 ± 2 and 62 ± 1 μM, respectively, which exceeds the previously reported maximum concentrations for C60 more than 6-fold; for C70 such an aqueous dispersion is prepared for the first time. The residual quantity of the organic solvent and low-molecular compounds determined by headspace GC-MS was not more than 1 ppb. The procedure for the determination of fullerenes in aqueous dispersions is developed using a total organic carbon analyzer and absorption spectra; LOD, 50 nM, LOQ, 200 nM by TOC. Spectrophotometric determination of fullerenes in their aqueous dispersions was optimized: for C60 at 268 nm: LOD, 0.1 μM, LOQ, 0.3 μM, for C70 at 218 nm: LOD, 0.1 μM, LOQ, 0.3 μM. RSD mixture quantification by Vierordt’s method in the range of 2 – 20 μM does not exceed 0.14 for C60 and 0.09 C70. RSD for toluene fullerene mixtures by Vierordt’s method in the range of 2 – 20 μM does not exceed 0.10 for C60 and 0.06 for C70.

Application of Thermal Lens Spectrometry to the Study of Chemical Adsorption in a Layer of a Nafion Solid Electrolyte

Thermal lens spectrometry was used to study Langmuir–Blodgett films of a weakly absorbing Nafion polyelectrolyte membrane on the surface of inert polyethylene terephthalate (PET) and glass substrates and to estimate the amount of Nafion (number of layers) using a change in the thermal characteristics of the sample. The sensitivity of thermal lens measurements at the wavelength of the exciting radiation 532.0 nm is comparable to that of solid-state spectrophotometry in the region of the maximum absorbance of Nafion (275 nm). However, the high locality of thermal lens spectrometry (the area of the signal generation zone is 100 μm2) ensures the estimation of the uniformity of the deposition of the polyelectrolyte layer. To increase the absorbance of the layer of the applied polyelectrolyte, the latter is saturated with a colored compound (ferroin). The adsorption of ferroin into the Nafion layer on the PET surface was confirmed; the absorbance of ferroin in the Nafion layer is in the range of 1 × 10–5–5 × 10–4 units of absorbance, which corresponds to the surface concentration of ferroin 1 × 10–11–4 × 10–10 mol/cm2.

Determination of Adsorbates on the Surface of Polymer with Low Absorption Capacity by Thermal Lens Spectrometry

Thermal lens spectrometry in a coaxial configuration is used for the direct determination of adsorbates on a planar surface of polyethylene terephthalate (PET). A possibility of the direct measurement of the rate of adsorption from solutions and the determination of the parameters of the adsorbed layer is demonstrated by the example of an investigation of the adsorption of iron(II) tris(1,10-phenantrolinate) on a PET surface. The adsorption isotherm of iron(II) tris(1,10-phenantrolinate) on the PET surface is described by the Langmuir equation and is linear in the concentration range in solution from 0.02 to 0.7 mM. The method for calculating the thermal perturbation in surface-absorbing solids was used to interpret the results of the adsorption study, and a possibility of determining iron(II) tris(1,10-phenantrolinate) on the surface at a level smaller than a monolayer was shown. Thermal lens spectrometry enables the determination of the absorption of the surface layer at a level up to 5 × 10–5 absorbance units, which corresponds to the surface concentration of iron(II) tris(1,10-phenanthrolinate) 2 × 10–13 mol/cm2. Using the example of the adsorption of 4-(2-pyridylazo) resorcinol on the PET surface, it is demonstrated that, in the case of strong absorption of the surface layer, the thermal destruction of substance and the deformation of the substrate may occur. A local increase in temperature in the layer is also confirmed by theoretical calculations.

Two-Laser Thermal Lens Spectrometry with Signal Back-Synchronization

A two-laser dual-beam thermal lens spectrometer based on continuous-wave lasers, which implements the mode with signal back-synchronization, is developed with the aim to develop instrumentation for thermal lens spectrometry. This mode offers a potentially higher sensitivity of measurements in comparison with the lock-in mode of thermal lens measurements and variation of conditions depending on the measurement medium (solvent, or dispersed system, or solids). The wider possibilities of the back-synchronization mode in thermal lens spectrometry both for solving problems of chemical analysis and in some related fields are shown.

Application of Microwave Plasma Atomic Emission Spectrometry and Hydride Generation for Determination of Arsenic and Selenium in Mineral Water

The ability to determine arsenic and selenium at their maximum acceptable concentrations (MAC) in drinking water via microwave plasma atomic emission spectrometry (MP-AES) and hydride generation is shown in this study. The determination of these elements is possible even in samples with a high degree of mineralization (up to 12 g/L). To provide the required sensitivity of determination of both elements, certain operating modes of the spray chamber for hydride generation are chosen. The conditions for the determination of these elements in mineral and medical-table waters are proposed.

Impact of a physiological medium on the aggregation state of C60 and C70 fullerenes

The C60 and C70 fullerene-cluster size distribution in aqueous solutions and a physiological medium is studied via dynamic light scattering. The initial aqueous solutions of fullerenes obtained via different methods are found to contain clusters with a characteristic size of about 100 nm. The additional aggregation of fullerenes is observed after their transfer into a physiological medium (0.9% NaCl) and is established to depend on the preparation method. The cluster-size distribution in a fullerene–pectic-acid mixture is found to vary in water and a physiological medium. The results reveal the need for additional studies of the structure and properties of C60 and C70 molecules, as well as their complexes with medicines, in a physiological medium for medical applications.