Analytica, Volume 3, Issue 1 (March 2022) – 11 articles

Pazopanib (PAZ), a tyrosine kinase inhibitor, is used to treat advanced renal cell carcinoma (RCC) and advanced soft tissue sarcoma (STS). The FDA approved PAZ for RCC in 2009 and for STS in 2012. The antitumor activity of pazopanib, according to the degree of inhibition, shows different results depending on the dose. Renal cell carcinoma is the most sensitive carcinoma to pazopanib, with 77% inhibition at the 10 mg/kg dose. Clinical studies have shown 53% to 65% inhibition in carcinomas such as breast carcinoma, prostate carcinoma, and melanoma. Plasma proteins such as human serum albumin (HSA) have a critical role in transporting and storing bioactive components. This feature of HSA is very important for the development of cancer therapy. Here, we investigated the interaction between PAZ and HSA to evaluate their binding strength, binding types, and conformational change in HSA. We used spectroscopic methods to assess the drug–protein interaction. Fluorescence measurements revealed that the interaction of PAZ with HSA occurred via the static quenching mechanism. The calculated binding number and binding constants were 1.041 and 1.436 × 10⁶ M⁻¹, respectively, at 298.15 K based on fluorescence screening. The high binding constant and calculated Gibbs free energy at different temperatures showed spontaneous and strong binding. Circular dichroism measurements showed that the α-helix structure of HSA was retained as the secondary structure, with a slight reduction in its percentage after adding PAZ. Furthermore, molecular modeling studies suggested that the docking score of PAZ is higher than those of bicalutamide and ibuprofen, the drugs that were chosen as model competitors against PAZ. Accordingly, PAZ was found to replace bicalutamide and ibuprofen on the HSA binding site, which was also confirmed by UV absorption spectroscopy. Full article

There is an increasing worldwide demand for rare earth elements (REEs) in new technological applications—such as electronics, superconductors, space applications, etc. The determination of low concentration REEs in geological samples is extremely important since they are the source materials for all REE products. In order to improve the accuracy and precision of REE measurements by inductively coupled plasma mass spectrometry (ICP-MS); complete digestion of refractory phases and minerals in the samples, low procedural blanks, separation of interfering matrix, and elimination of interference on the mass of the analytes of interest must be fulfilled. Conventional methods that use a hotplate and a mixture of four acids are effective but can take time to achieve complete dissolution of samples that contain highly refractory phases, which is unacceptable in the mining and metallurgical industry. Such difficult samples necessitate high-temperature alkaline flux fusion as it offers a faster and more efficient alternative to acid digestion. This paper presents an accurate, precise, rapid, and reliable method for rare earth element analysis by ICP-MS with low detection limits, which involves no sample pre-concentration, and is therefore able to deliver data rapidly. The analytical performance of the developed method was tested successfully on various REE rock-type certified reference materials and evaluated statistically. The results obtained were in reasonable agreement with published certificate values. Full article

Oil media on paper, such as oil paintings, sketches, prints, and books, occasionally present problems associated with the effect of oil medium on the paper support, raising a composite matter of condition assessment as it depends on several factors. The present work examines the effect of linseed oil on paper and, in particular, the changes caused by three types of linseed oil on the optical, morphological, mechanical, and chemical properties of pure cellulosic paper, employing mock-ups submitted to artificial ageing in controlled conditions of relative humidity and temperature in airtight vessels. The study involved colorimetry, opacity, tensile strength, pH measurements, SEM, FTIR, and VOC analysis with GC-MS. Processing of the results has so far indicated that thermal-humid ageing caused the gradual darkening of the oil-impregnated mock-ups, as well as alterations in opacity, intense fall of pH values, and severe reductions in tensile strength, while linseed oil processing during manufacture has a significant impact. FTIR spectra have indicated that chemical changes upon ageing are in accordance with those of optical and mechanical changes, while VOC emissions are mostly associated with the drying and degradation of the different types of linseed oil. Full article

Aluminum Carbide (Al₄C₃) is a main source of corrosion problems in metal matrix composites as well as refractory products. Hydrolysis to methane happening at room temperature leads to various structural problems. As methods to quantify Al₄C₃ are scarce, this paper proposes a method to measure Al₄C₃ containing analyte powders in mg areas by combining a robust autoclave system with non-dispersive infrared (NDIR) process analytics. The method uses only water as reagent, making it easy and safe to handle. The used materials were characterized by thermogravimetric analysis coupled with fourier-transformation infrared detection (TGA-IR), LECO-C analysis, and X-ray diffraction (XRD) before and after autoclave treatment. 90–90.8% recovery of 100 mg Al₄C₃ with small standard deviations (<1% at n = 3) in 240, 205, and 165 min at 60, 70, and 80 °C, respectively, were achieved. XRD analysis showed the total conversion of Al₄C₃ to Bayerite (Al(OH)₃) and Boehmite (AlO(OH)) at 70 °C. Comparison with shrinking core models showed that the reaction is neither purely reaction nor purely ash diffusion controlled. The findings indicate possibilities for further acceleration of reaction speeds by increasing temperature. The 200 mL reactor volume of the autoclave enables the analysis of bigger sample sizes at temperatures above 100 °C by separating reaction and analysis procedure. This provides an extension to gas chromatographic methods for industrial quality control of bulk materials in rougher environments. Full article

This work presents the first development of an all-steps-in-one test kit for the determination of paraquat in natural water, and vegetable and agricultural samples. A handheld photometer incorporated with a magnetic stirrer was used to complete the steps of extraction, mixing, and detection. Paraquat produces a blue free radical ion via a reduction with sodium dithionite in alkaline conditions. Sodium dithionite powder was investigated for the enhancement of reagent stability duration, which was added directly into sample solution that showed insignificant difference in sensitivity as compared with that of the solution format of sodium dithionite. The developed test kit showed good performance with the linear calibration of 0.5 to 10 mg L⁻¹ with a high coefficient of determination (r² = 0.9947). The lower limit of quantitation (LLOQ = 3SD of intercept per slope) carried out from the method using the handheld photometer was 0.50 mg L⁻¹. The limit of detection (LOD) by naked eye was 0.30 mg L⁻¹. The recovery study was acceptable in the range of 101–115%. Intraday (n = 3) and interday (n = 3) precision was less than 1%. On the basis of the significance test at the 95% confidence interval, quantitative results of the developed test kit agreed well with those from high-performance liquid chromatography (HPLC). To the best of our knowledge, this is the first report demonstrating an online extraction for vegetables incorporated into a test kit, applicable for on-site analysis. Single-point calibration based on the Beer–Lambert law also demonstrated the measurement of paraquat. In testing with a nominal standard solution of 5.00 mg L⁻¹ paraquat, the reading concentration was 5.09 ± 0.03 mg L⁻¹ paraquat (n = 20) with a K value of 0.0967 (close to the slope of multipoint calibration). This research is a direct benefit to agricultural products and the health of a population for the analysis of pesticides and herbicides. Full article

Cetrimide (CE) is a quaternary ammonium compound and a cationic surfactant, which can be used as an antiseptic and preservative in various formulations. Antiseptic solutions of Cetrimide are available in combination with Chlorhexidine Gluconate (CHG) for external use. Chlorhexidine is a biguanide with high microbicidal activity and is widely known as a skin disinfectant. The present work displays the development and validation of an RP-HPLC isocratic method for the simultaneous determination of CE and CHG. The method consists of a Hypersil^® SAS C1 (4.6 × 250 mm) 5 μm column, with a mobile phase of 85%/15% v/v MeOH-NaH₂PO₄·H₂O, aqueous solution. In addition, 0.2% of triethylamine (Et₃N) was added to the buffer for the confrontation of peak tailing, and then the pH was adjusted to 3.0 with ortho-phosphoric acid (H₃PO₄). The flow rate was set at 1 mL/min, and adequate detection was achieved with a diode array detector (PDA) at 205 nm. The method was successfully validated according to ICH guidelines for specificity, linearity, accuracy, precision and stability for sample and standard solutions. In addition, the robustness of the method was evaluated through statistical and graphical analysis, using a fractional factorial experimental design. Full article

This review would like to show the state of the art regarding the coupling of High-Performance Liquid Chromatography (HPLC) with Electrochemical Detection (ED). Since a universal detector for HPLC is not available, the electrochemical detection methods, thanks to their versatility and specificity, are competitive with respect to the detectors currently used. The papers present in literature on HPLC-ED technique are analyzed and discussed: for example, they regard the development of analytical determinations of resveratrol, rosmarinic acid, aromatic heterocyclic amines and glyphosate in food matrices such as meat, aromatic plants, vegetables, fruit and tomato juices. These papers show that electrochemical sensors used as detectors for HPLC can offer better sensitivity values than other detectors. Furthermore, the use of specific working potentials allows avoid matrix interferences to be avoided by almost exclusively determining the analytes of interest. It should be underlined that HPLC-ED methods have a selectivity that allows for limitation of the sample preparation and clean-up procedures to a minimum, making them quick and easy to apply. In addition, these methods offer advantages such as the possibility of direct analysis, that derivatization is often not necessary, the cost-effectiveness of the instrumentation and the possibility of regenerating the electrodes which allows numerous analyses in succession. Full article

Reversed micelles are helpful to solubilize otherwise insoluble membranotropic or membrane-bound enzymes in their functional form, thus enabling activity assay and inhibition analysis. However, in the case of redox enzymes, this task is further complicated by the necessity to select an appropriate electron-acceptor (EA) which, ideally, should be compatible with spectrophotometric measurements in reversed micelles. Here, we have identified such an EA and successfully used it in a reversed micellar environment to assay the activity of two homologous enzymes from mitochondria: l-galactone-1,4-lactone dehydrogenase (EC 1.3.2.3) from Arabidopsis thaliana (AtGALDH) and galactonolactone oxidase (EC 1.3.3.12) from Trypanosoma cruzi (TcGAL), differing in their membranotropic properties, with TcGAL being almost insoluble in water and particularly difficult to assay. Furthermore, we have demonstrated the possibility to use this assay for inhibition analysis, with an elucidation of the mechanism and inhibition parameters, which otherwise could not be possible. In order to perform inhibition analysis, we improved the approach for the determination of activity of such membrane enzymes based on a reversed micellar system as membrane matrix, necessary for the functioning of membrane enzymes. A number of electron acceptors (EA) were tested for AtGALDH and optimal conditions of activity determination for AtGALDH were found. The suggested method was successfully applied to the study of the inhibition of AtGALDH by lycorine, and the mixed competitive mechanism of inhibition of AtGALDH by lycorine was determined. The developed approach to inhibitor analysis was applied for TcGAL, insoluble in water membrane, and the method provides new opportunities for searching effective inhibitors that may be potential drugs. Indeed, galactonolactone oxidase from Trypanosoma cruzi (TcGAL) and AtGALDH are homologues, and the inhibition of TcGAL stops the vital biosynthesis of vitamin C in parasite Trypanosoma cruzi from causing Chagas disease. The approach proposed can be applied for the screening of inhibitors of AtGALDH and TcGAL, as well as to study properties of other membrane enzymes including determination of the mechanisms of inhibition, structure and catalytic properties, the impact of membrane components (for example lipids), and so on. Full article

This communication introduces the first-time application of high-resolution continuum-source molecular absorption spectrometry (HR CS MAS) for the quantification of a peptide. The graphite furnace technique was employed and the tripeptide glutathione (GSH) served as a model compound. Based on measuring sulfur in terms of carbon monosulfide (CS), a method was elaborated to analyze aqueous solutions of GSH. The most prominent wavelength of the CS molecule occurred at 258.0560 nm and was adduced for monitoring. The methodological development covered the optimization of the pyrolysis and vaporization temperatures. These were found optimally to be 250 °C and 2250 °C, respectively. Moreover, the effect of modifiers (zirconium, calcium, magnesium, palladium) on the absorption signals was investigated. The best results were obtained after permanent coating of the graphite tube with zirconium (total amount of 400 μg) and adding a combination of palladium (10 µL, 10 g L⁻¹) and calcium (2 µL, 1 g L⁻¹) as a chemical modifier to the probes (10 µL). Aqueous standard samples of GSH were used for the calibration. It showed a linear range of 2.5–100 µg mL⁻¹ sulfur contained in GSH with a correlation coefficient R² > 0.997. The developed method exhibited a limit of detection (LOD) and quantification (LOQ) of 2.1 µg mL⁻¹ and 4.3 µg mL⁻¹ sulfur, respectively. The characteristic mass accounted for 5.9 ng sulfur. The method confirmed the general suitability of MAS for the analysis of an oligopeptide. Thus, this study serves as groundwork for further development in order to extend the application of classical atomic absorption spectrometry (AAS). Full article

Synthetic cathinones are analogue compounds of the plant based stimulant cathinone. Its use, abuse, and related consumption complications have steadily increased in the last years. For this reason, there is a need for innovative analytical approaches that enable its rapid screening in biological matrices (e.g., oral fluids). The present work proposes a new analytical methodology by combining bar adsorptive microextraction followed by microliquid desorption and gas chromatography coupled to mass spectrometry (BAµE-µLD/GC-MS) for screening three synthetic cathinones (α-PVP, α-PVT, and MDPV) in oral fluids. The optimization of the BAµE-µLD/GC-MS methodology was successfully applied for the analysis of the target compounds in oral fluids. The results show average recoveries between 43.1 and 52.3% for the three synthetic cathinones. Good selectivity was also noticed. The developed methodology presents itself as an alternative tool to screen these compounds in oral fluids. To the best of our knowledge, this is the first work that combines a microextraction sorption-based technique followed by GC-MS analysis for the screening of synthetic cathinones in oral fluids. Full article

The topic of hexavalent chromium (Cr(VI)) in leather has been debated throughout the whole supply chain for years. However, its significance has recently increased due to proposed changes in European legislation concerned with skin-sensitising substances suggesting that acceptable Cr(VI) concentrations in leather goods should be lowered from 3 mg kg⁻¹ to 1 mg kg⁻¹. The proposition of a stricter limit and current analytical difficulties created the need for a review of current standard test methods. The research presented in this paper investigates both the colorimetric (Part 1) and chromatographic (Part 2) methods under BS EN ISO 17075. The focus of the study was to identify possible sources of interference leading to large statistical variance in results and to define the limit of quantification with respect to the proposed new compliance limit. This study into the colorimetric method has shown that the presence of Cr(III), dyes, and proteins can be significant interferences, becoming critical at low Cr(VI) concentrations. Dilution factors worsen the problem of detecting low concentrations: a reliable quantitative detection of 0.01 mg kg⁻¹ and 0.003 mg kg⁻¹ Cr(VI) in solution are required at the 3 mg kg⁻¹ and 1 mg kg⁻¹ compliance limits in leather, respectively. BS EN ISO 17075 part 1 was shown to be incapable of reliably resolving to 3 mg kg⁻¹ or below in leather. Part 2 shows a marked improvement in detection limits and reliability; however, data suggest that 1 mg kg⁻¹ Cr(VI) is not reliably detectable in leather. Suggested improvements to the established test methods and a possible alternative are discussed. Full article