Armağan Önal

Phenolic acids (PAs) are among the most abundant phytochemicals in foods and plants, and their consumption is increasing due to well-established health benefits. Determining these compounds is challenging because of their structural diversity, wide concentration ranges, and complex matrices. This review summarizes the separate analysis of PAs in foods, plants, and plant-based foodstuffs, with a particular focus on gas chromatography (GC) methodologies. Since PAs are inherently nonvolatile, chemical derivatization is generally required to enhance volatility and reduce polarity, enabling accurate detection. The role of derivatization, together with the extraction approaches used to isolate PAs from complex matrices, is critically discussed. Additionally, the review covers key method validation parameters, such as analytical range, limit of detection, and limit of quantification, that are essential for accurate measurement of PAs. By focusing on GC-based approaches, this review highlights their contribution to improving analytical performance and supporting research on PAs in food and plant sciences.

A rapid ultra-performance liquid chromatographic method coupled with a quadrupole detector (UPLC–QDA) was developed and validated for the simultaneous determination of pinaverium bromide, medazepam, and their related substances in a newly developed fixed-dose pharmaceutical formulation. Chromatographic separation was achieved on an Acquity BEH C18 column (100 × 2.1 mm, 1.7 µm) using a gradient elution of 25 mM ammonium formate buffer (pH 3.5) and acetonitrile at a flow rate of 0.6 mL/min and a column temperature of 45 °C. The total run time was 11 min, providing complete resolution of all analytes without interference. Linearity was demonstrated (R² ≥ 0.999) within the ranges of 2–400 ng/mL for medazepam, 10–2000 ng/mL for pinaverium bromide, 5–1000 ng/mL for RS1 (medazepam impurity), and 10–2000 ng/mL for RS3–RS6 (pinaverium bromide impurities). The limits of detection (LOD) and quantitation (LOQ) were 0.17 and 0.50 ng/mL for medazepam and 0.43 and 1.30 ng/mL for pinaverium bromide, respectively, while LOD and LOQ values for related substances ranged between 0.22–0.91 ng/mL and 0.66–2.70 ng/mL. The method was validated in accordance with the ICH Q2(R2) guideline. The validated method was successfully applied for the simultaneous quantification of pinaverium bromide, medazepam, and their respective impurities (RS1–RS6) in commercial film-coated tablets (50 mg/10 mg), demonstrating its applicability for routine quality control and stability testing of fixed-dose combination formulations.

A novel analytical method based on ultra-fast liquid chromatography using fluorimetric detector was developed and validated for determination of non-steroidal anti-inflammatory drugs (NSAIDs) (ibuprofen (IBP), etodolac (ETD), dexketoprofen (DKP), sodium diclofenac (SDCF), and naproxen (NPX) in tap water, urine and pharmaceutical samples. Precolumn derivatisation of targeted NSAIDs was carried out with 4-bromomethyl-7-methoxy coumarin (BrMmC) using dibenzo-18-crown-6-ether as reaction catalyst leading to the formation of a fluorescent compound. The obtained fluorescent compound of NSAIDs were measured at excitation wavelength as 325 nm, and emission wavelength of 395 nm. Optimum analytical conditions were carefully studied and improved. C18 column, with the dimensions of 4.0 × 100 mm and 3 µm particle size, was used. Gradient elution with methanol: water 40:60; v/v (eluent A) and acetonitrile 100% (eluent B) were used as mobile phase and flow rate of 0.4 mL/min. The linearity range of the analytes were between 0.01–10.0 µg mL⁻¹. Recovery values obtained from pharmaceutical preparations were found as 100.04%, 99.99%, 100.09%, 99.98% and 100.47% for IBP, ETO, DKP, SDCF, NPX, respectively. LOD values were found to vary between 0.00009 µg mL⁻¹ and 0.00048 µg mL⁻¹ in tap water, urine and pharmaceutical samples. The optimised technique was successfully applied for the determination of NSAIDs in tap water, urine, and pharmaceutical specimen. The specified NSAIDs were not found in real tap water samples.

A simple and sensitive analytical procedure by solid-phase extraction method combined with high-performance liquid chromatography and using of graphene–magnetite nanomaterials as sorbent has been developed for the determination of atorvastatin in human plasma. A magnetic solid-phase extraction method as a simple, fast, and efficient extraction technique has been used for sample preparation. A solid nanocomposite material, graphene nanosheets decorated with magnetite nanoparticles, was used as a magnetic adsorbent and the adsorption process was optimized in this study. RP C18 column was used with mobile phase composed of acetonitrile–10 mM orthophosphoric acid by isocratic elution with the flow rate of 1 mL min⁻¹. Fluorimetric detection was used by the excitation wavelength at 282 nm and the emission wavelength at 400 nm. It was found that the calibration curve was linear in the 30–150 ng mL⁻¹. Limit of detection and limit of quantitation values were found to be 10 and 30 ng mL⁻¹, respectively. The intra-day and inter-day relative standard deviation values were less than 5.27%. It has been concluded that the new developed method provides fast, simple, cost reduced, and sensitive assay for atorvastatin determination in human plasma. This method is also applied to a pharmacokinetic study. GRAPHICAL ABSTRACT

Two new simple and selective assay methods have been presented for the analysis of eprosartan mesylate (EPR) and hydrochlorothiazide (HCT) in pharmaceutical formulations. The first method is based on first-derivative ultraviolet spectrophotometry with zero-crossing measurements at 246 and 279 nm for EPR and HCT, respectively. The assay was linear over the concentration ranges 3.0–14.0 µg/mL for EPR and 1.0–12.0 µg/mL for HCT. The quantification limits for EPR and HCT were found to be 1.148 and 0.581 µg/mL, respectively, while the detection limits were 0.344 µg/mL for EPR and 0.175 µg/mL for HCT. The second method involved isocratic reversed-phase liquid chromatography using a mobile phase composed of acetonitrile–10 mM phosphoric acid (pH 2.5) (40:60, v/v). Olmesartan was used as internal standard and the substances were detected at 272 nm. The linearity ranges were found to be 0.5–30 and 0.3–15.0 µg/mL for EPR and HCT, respectively. The limits of detection were found to be 0.121 µg/mL for EPR and 0.045 µg/mL for HCT. The limits of quantification were found to be 0.405 and 0.148 µg/mL for EPR and HCT, respectively. The proposed methods were successfully applied to the determination of commercially available tablets with a high percentage of recovery and good accuracy and precision.