Novel sorbents with various zwitterionic fragments in the functional layer structure with varying branching were used to determine organic acids, sugars, nucleosides, and vitamins in various samples. For all studied analyte classes, a decrease in efficiency was observed with an increase in sorbent functional layer. Therefore, a less branched stationary phase, obtained using 1,4-butanediol diglycidyl ether and glycine, was used to determine nucleosides and nitrogenous bases in bacterial nutrient media. For water-soluble vitamins, the complete resolution of thiamine and nicotinamide was achieved using a sorbent with a more branched layer containing taurine in its core. It was found that the decrease in efficiency with an increase in layer branching is compensated for by an increase in the strength and number of zwitterion acid groups in the stationary phase structure for organic acids. As a result, a sorbent with taurine and iminodiacetic acid in the branched layer structure, with the best separation capacity, exceeding that of known phases, was selected for the determination of organic acids in various beverages. The use of taurine in the hyperbranched layer also improved selectivity and increased efficiency for carbohydrates. As a result, a sorbent with glycine in the inner layer and taurine in the outer layer was used for the rapid determination of carbohydrates in sweet drinks. Analytes were identified by comparing their retention times with the retention times of peaks in standard solutions. The calibration curve range was selected based on the expected concentrations in the analyzed samples, as well as the solubility of analytes in the aqueous-organic mobile phase. The accuracy of results was confirmed using the “introduced and found” method. Concentrations of compounds of various classes in the analyzed samples, obtained using the novel stationary phases, correspond to those declared by the manufacturers.
Rapid advances in telecommunication systems operating at frequencies of 30 GHz and above (including 5G systems) require that materials having a dielectric constant under 2.2 and compatible with printed circuit board technology be designed and produced. Technological approaches to the fabrication of such materials build on forming air cavities in a starting dielectric matrix and require control over their microwave parameters (primarily over their dielectric permittivity and dielectric loss tangent) in the frequency range of interest. In this paper, we report our findings on the dielectric properties of a low-permittivity composite dielectric material. Hermetically sealed dielectric plates with a particular distribution of air cavities over their bulk were fabricated using mechanical perforation and 3D printing additive technology. Microwave parameters of the specimens obtained were determined at a frequency of 10 GHz using a dismountable cylindrical resonator. We studied specimens with a minimum dielectric permittivity of 1.75. It has been shown that, because of a number of specific features, the use of 3D printing additive technologies leads to changes in the geometric dimensions of forming air cavities, which in turn influences the dielectric properties of the material. The results obtained in this study can be useful in designing new microwave materials.
The ability to accurately and reliably determine dielectric properties of materials is critical for the development of microwave electrotechnologies. This is especially important for materials having wide ranges of dielectric permittivity and dielectric losses, in which case conventional analysis methods are insufficiently sensitive or too complex. The purpose of this work is to determine dielectric characteristics of materials using a volume resonator at a frequency of 2.45 GHz. We analyze a number of resonator parameters, such as resonance frequency and Q-factor, which are used to determine the dielectric properties of materials. Numerical simulation of the resonator is used to assess the electric and magnetic field distributions of the fundamental mode TM010 in it. Analysis of excitation conditions of the fundamental and parasitic modes demonstrates that they influence resonator parameter measurement accuracy and determination of dielectric properties of materials. The calculated dielectric permittivity and loss tangent of materials are shown to agree well with data in the literature (uncertainty of 3 and 6
A technique has been developed for determination of platinum and palladium in refining liquors by inductively coupled plasma atomic emission spectrometry (ICP-AES) with preconcentration on a synthetic carbon sorbent. The concentration of the platinum group metals in the solutions studied was below the quantification limit of the ICP-AES method ( 0.1 mg/dm3). We have determined the dynamic exchange capacity (DEC) of the sorbent in the case of platinum and palladium preconcentration: the DEC is (0.7–1.6) × 10–3 mg/g for Pt and (0.7–0.9) × 10–3 mg/g for Pd, depending on the type of process liquor. Using the DEC values, we have calculated the effective sorbent weight needed to ensure platinum and palladium recovery, which has been determined to be 155.9 g. To extract platinum and palladium from a test solution, it is passed through a sorbent-packed column for 4 h, and the analytes are eluted with aqua regia and then determined in the eluate by the ICP-AES method. Platinum recovery in the sorption preconcentration step is 98.7–99.3
Kh13-type martensitic steels are widely used, for example, in the manufacture of medical tools. In this paper, we report our results on the susceptibility of 20Kh13 and 40Kh13 steels to intergranular corrosion (IGC) in the as-received state (after hot rolling) and after heat treatment (spheroidizing annealing), studied by the AMUF rapid method. The microstructure of the steels has been examined by scanning electron microscopy, and their chemical composition and hardness have been determined. The results demonstrate that, after annealing, 20Kh13 steel has a higher susceptibility to IGC than does 40Kh13, even though they are similar in structural characteristics. This is related to differences in the morphology of the carbide phase: the finer and more uniformly distributed carbide grains in 40Kh13 ensure better corrosion resistance. The results obtained in this study can be useful for improving the technique for assessing the susceptibility of martensitic steels to IGC and, accordingly, more reliably evaluating the quality of medical tools and predicting their lifetime.
