Journal of Chemical Metrology

Reference materials (RMs) are essential for ensuring metrological traceability in various fields, including environmental monitoring, chemical analysis, and the verification of alcohol breath analyzers. One critical property of RMs is their long-term stability, particularly for gas mixtures such as ethanol in nitrogen, which are stored in pressurized aluminum cylinders. This paper describes the preparation of such gas mixtures according to ISO 6142-1, utilizing differential weighing to minimize the influence of ambient conditions and ensure accurate composition. The effects of adsorption of ethanol on the internal surfaces of aluminum cylinders were experimentally investigated. Results indicate that ethanol can remain adsorbed on the cylinder walls even after evacuation, leading to measurable ethanol concentrations upon subsequent refilling with nitrogen. Repeated fillings demonstrated a decrease in ethanol levels, confirming the saturation and gradual desorption behavior. These findings underscore the necessity to consider adsorption effects in the uncertainty budget and composition calculations for low-concentration ethanol-in-nitrogen RMs.

The accuracy and reliability of conductivity measurements in analytical laboratories depend significantly on the availability of quality control materials. This study addresses the preparation, homogeneity, stability and characterization of a potassium chloride (KCl) quality control material (QCM) of 1414 µS/cm based on ISO/TR 33402. OIML R-56 does not contain this conductivity value as a secondary standard, so the mass of KCl required to prepare such a solution was experimentally defined. The conductivity measurements were carried out at 25 °C using a conductivity meter calibrated by a CRM produced by the the Slovak Institute of Metrology (SMU), a signatory to the mutual recognition arrangement (MRA) of the International Committee of Weights and Measures (CIPM). The homogeneity study was carried out in accordance with ISO 33405 using 10% of the batch bottles and the analysis of variance (ANOVA) showed that the QCM batch is homogeneous. The short-term stability was carried out over 4 weeks storage time at 4°C and 40°C and the isochronous measurements showed no significant deviations over time. The characterization of the QCM along three days showed that, its conductivity was 1414.11 µS/cm. The uncertainty associated with the conductivity measurements was assessed based on the requirements of the Guide to the expression of uncertainty in measurement (ISO GUM) and the EURACHEM/CITAC Guide, CG4 (Quantifying uncertainty in analytical measurement). It was found to be 23.10 µS/cm or 1.63%. A control chart was developed using the prepared QCM and the measured values remained within the control limits over the control time of six weeks. The prepared KCl QCM will be useful for use in quality control and instrumental validation in food, drug and environmental conductivity testing.

The study aims to identify the secondary metabolites of Hypericum aucheri Jaub. & Spach extracts using liquid chromatography-high resolution mass spectrometry (LC-HRMS) and to evaluate the plant's antioxidant activity. Antioxidant activity was assessed using DPPH free radical scavenging and CUPRAC assays. The primary secondary metabolite detected was hyperoside, with concentrations of 1059.53 mg/L in acetone (Ac) extract and 389.73 mg/L in methanol (MeOH) extract. Sinapinic acid was the predominant compound in the chloroform (C) extract, with a concentration of 6646.53 mg/L. In addition, Ac extract showed the highest DPPH free radical scavenging activity (85.90±0.26 - 61.19±0.47%) of all the extracts tested. The MeOH extract exhibited the highest value in the CUPRAC assay (2.53±0.05 mmol TR g-1). The study highlights a numerical relationship between phenolic content and antioxidant activity, underscoring the importance of phenolics in their antioxidant functions.

This study reports the development and validation of a novel, rapid, and stability-indicating reversed-phase high-performance liquid chromatography (RP-HPLC) method for the quantification of pazopanib in tablet formulations. Chromatographic separation was achieved on an Inertsil ODS-3V column (150 mm × 4.6 mm, 5 µm) using an isocratic mobile phase of 0.1% trifluoroacetic acid and acetonitrile (70:30, v/v) at a flow rate of 1.0 mL/min with UV detection at 268 nm. The method demonstrated excellent resolution of pazopanib from its degradation products under forced degradation conditions, including acid/base hydrolysis, oxidation, photolysis, thermal, and humidity stress, confirming its stability-indicating capability. Validation in accordance with ICH Q2(R1) guidelines showed linearity over 25.71, 51.41, 82.26, 102.82, 123.38, and 154.23 µg/mL (r² > 0.999), precision with %RSD < 2.0, accuracy with recovery > 99%, and robustness under deliberate variations in chromatographic parameters. The limit of detection (LOD) and limit of quantification (LOQ) confirmed high sensitivity, and solution stability studies established analyte stability over 24 hours at 25 °C. With a runtime of 20 minutes and cost-efficient operation, this RP-HPLC method provides accurate, precise, and selective quantification of pazopanib in pharmaceutical dosage forms.