A feedback-mode variant of thermal lens spectrometry was employed for steady-state photothermal measurements and time-resolved studies of thermal lens formation dynamics to compare the precision and sensitivity of measurements in aqueous polyethylene glycol (PEG) solutions of different molecular weights using a series of model systems (ferroin, cobalt complexes with nitrosonaphthols, and aqueous fullerene dispersions). The results of thermal lens measurements obtained in single-phase aqueous PEG solutions were compared with those obtained under extractive preconcentration conditions in PEG-based aqueous two-phase systems. Time-resolved thermal lens development curves in PEG-containing media were shown to exhibit greater stability and improved temporal separation between the thermal lens effect itself and the interfering thermophoresis phenomenon (the Soret effect) than those recorded in polymer-free aqueous media. To improve the accuracy of thermal diffusivity measurements, experimental conditions were selected under which the deviation from the theoretical curve development was minimal, and the Soret effect was absent (50–300 ms from the beginning of the measurement cycle). In PEG-containing media, the dynamics of thermal lens development showed better agreement with theory even for finely dispersed systems (aqueous fullerene dispersions), resulting in a substantial increase in the sensitivity of thermal lens measurements. The precision of thermal lens measurements in PEG solutions was higher than that in aqueous solutions because of lower signal fluctuations, which further enhanced the sensitivity of thermal lens measurements in such media. Conditions were proposed for the extraction-thermal lens determination of cobalt with 2-nitroso-1-naphthol based on the partitioning of the colored complex in an aqueous two-phase system composed of PEG and phosphate ions (K2HPO4, NaH2PO4, or NH4H2PO4), followed by thermal lens determination in the extract phase. The detection limit for cobalt with 2-nitroso-1-naphthol in the phosphate–PEG aqueous system was 1 μmol/L (532 nm, excitation laser power 10 mW), whereas the detection limit for cobalt with nitroso-R salt in the ammonium sulfate–PEG aqueous system (excitation laser power 100 mW) was 0.2 μmol/L. For aqueous fullerene dispersions, a twofold increase in measurement sensitivity was demonstrated compared with aqueous media without PEG.
Creatinine is a key marker for renal function, and accurate measurement of creatinine in serum is important for clinical diagnostics. In the present work, a new colorimetric method using the creatinine-chlorophenol red (CPR) reaction was introduced and conducted with ultraviolet-visible and paper-based microfluidic (µPAD) measurement. Optimal conditions were established for each method, whereas analytical performance in terms of linearity, sensitivity, precision, recovery, and comparison with the reference analyzer (Cobas c311) was evaluated. A spectrophotometric method based on the formation of a pink-violet ion-pair complex and its bathochromic shift with an absorption maximum at 576 nm was developed, linear over 2–130 µg/mL, the limit of detection (LOD) was 1.2 µg/mL, and the limit of quantification (LOQ) was 2.25 µg/mL. Finally, the µPAD-based assay was optimized using a higher CPR concentration (100 µg/mL) and had a linear range of 10–160 µg/mL (R2 = 0.9972), and LOD and LOQ were 7.0 and 11.57 µg/mL, respectively. Recovery values between 97.1 and 104.3
A version of competitive fluorescence polarization immunoassay (FPIA) and an amperometric immunosensor with a tyrosinase tracer have been developed for the sensitive and selective determination of the chloramphenicol antibiotic. In the development of FPIA for the determination of chloramphenicol, a green fluorescent complex of terbium(III) was first used as a tracer, which changed emission in the green spectral region with a maximum at 545 nm. The competitive binding of the substance to be determined with a limited number of binding sites of specific antibodies (ABs) in using this tracer ensured the determination of chloramphenicol in the linear range of the calibration dependence of fluorescence polarization on the analyte concentration in the range 1 × 10–11–1 × 10–7 M, LOD = 9 × 10–12 M. To ensure the maximum value of the analytical signal, tracer dilution was selected at 1 : 10 and antibody dilution, at 1 : 25. The optimal incubation time for the tracer–antibody immune complex was 5 min. Tyrosinase enzyme was used as a tracer in the development of an amperometric enzyme-linked immunosorbent assay (ELISA) sensor for the detection of chloramphenicol. The work of this sensor is based on a combination of immunochemical, enzymatic, and electrochemical reactions, leading to “quasi-inhibition” effects. The developed amperometric immunosensor for the determination of chloramphenicol ensured its determination in a narrower concentration range from 1 × 10–9 to 1 × 10–6 M, LOD = 8 × 10–10 M. The conditions of analysis were as follows: AB dilution of 1 : 200 and the duration of an analysis 10 min. The developed versions for the determination of chloramphenicol were tested in analyses of food products (milk). The error of the determination dis not exceed 0.059.
This paper presents the results of original research on nondestructive quality control of food products and solid dosage forms of pharmaceuticals using digital colorimetry with a smartphone and chemometric processing of the resulting spectral data.
Silica monolithic rods are inorganic materials used as packing materials in monolithic separation columns, a global trend in material separation, particularly in high-performance liquid chromatography (HPLC). Unlike the previously widely used separation columns with spherical silica packing, these monolithic columns suffer from various problems, including shrinkage, deformation, and cracking during the preparation of rods, limiting their application. This paper describes the development of a new type of silica monolithic rod that can significantly shorten analysis time while maintaining high separation efficiency in HPLC.
