Novel multiple extraction thermal desorption approach prior to gas chromatography for the determination of residual solvents applied to modified cellulose.

In this work, multiple extraction thermal desorption (METD), as a sample introduction method for GC, was developed. This technique was used for the determination of residual solvents (RS) in modified cellulose, because it is practically impossible to dissolve or distribute it uniformly in water and common organic solvents. Moreover, METD facilitates the optimization of the desorption time and it is more sensitive to quantify trace level volatiles in insoluble material, compared to direct dynamic desorption (DDD). In addition, METD provides diagnostic information about the sample-sorbent interaction. Three solvents (methanol, ethanol and tert-butanol) were determined in two types of modified cellulose (dialdehyde cellulose (DAC) and DAC-ethylenediamine (DAC-EDA)). It was shown that good linearity over a wide concentration range was achieved. The limits of detection (LOD) and limits of quantification (LOQ) for the different solvents ranged from 0.1 to 0.3 µg and from 0.3 to 0.9 µg per tube, respectively. Accuracy of the METD method was verified by using an alternative method based on the decomposition of the modified celluloses by Trichoderma reesei cellulase, followed by headspace-trap-GC (HS-trap-GC). The results obtained from the two validated methods were found to be similar (relative deviation < 17.0 %). However, the developed METD-GC method is preferable for the analysis of RS in modified cellulose since it does not require sample pretreatment and possesses higher sensitivity.

Quantification of amino acids secreted by yeast cells by hydrophilic interaction liquid chromatography-tandem mass spectrometry.

Monitoring the levels of amino acids (AAs) in biological cell cultures provides key information to understand the regulation of cell growth and metabolism. Saccharomyces cerevisiae can naturally excrete AAs, making accurate detection and determination of amino acid levels within the cultivation medium pivotal for gaining insights into this still poorly known process. Given that most AAs lack ultraviolet (UV) chromophores or fluorophores necessary for UV and fluorescence detection, derivatization is commonly utilized to enhance amino acid detectability via UV absorption. Unfortunately, this can lead to drawbacks such as derivative instability, labor intensiveness, and poor reproducibility. Hence, this study aimed to develop an accurate and stable hydrophilic interaction liquid chromatography-tandem mass spectrometry analytical method for the separation of all 20 AAs within a short 17-min run time. The method provides satisfactory linearity and sensitivity for all analytes. The method has been validated for intra- and inter-day precision, accuracy, recovery, matrix effect, and stability. It has been successfully applied to quantify 20 AAs in samples of yeast cultivation medium. This endeavor seeks to enhance our comprehension of amino acid profiles in the context of cell growth and metabolism within yeast cultivation media.

Raman spectroscopy: A promising analytical tool used in human reproductive medicine.

Over the past few years, there has been growing interest in developing new methods of embryo quality assessment to improve the outcomes of assisted reproductive technologies in the medical field. Raman microscopy as an increasingly promising analytical tool has been widely used in life sciences, biomedicine and "omics" to study molecular, biochemical components, living cells and tissues due to the label-free and non-destructive nature of the imaging technique. This paper reviews the analytical capability of Raman microscopy and applications of Raman spectroscopy technology mainly in reproductive medicine. The purpose of this review is to introduce the Raman spectroscopy technology, application and underlying principles of the method, to provide an intact picture of its uses in biomedical science and reproductive medicine, to offer ideas for its future application, verification and validation. The focus is on the application of Raman spectroscopy in the reproductive medicine field, including the application in gametes, embryos and spent embryo culture media.

Development and Validation of Liquid Chromatographic Method for Fast Determination of Lincomycin, Polymyxin and Vancomycin in Preservation Solution for Transplants.

In this study, a liquid chromatographic method was developed for the fast determination of lincomycin, polymyxin and vancomycin in a preservation solution for transplants. A Kinetex EVO C18 (150 × 4.6 mm, 2.6 µm) column was utilized at 45 °C. Gradient elution was applied using a mixture of mobile phases A and B, both including 30 mM phosphate buffer at pH 2.0 and acetonitrile, at a ratio of 95:5 (v/v) for A and 50:50 (v/v) for B. A flow rate of 1.0 mL/min, an injection volume of 20 µL and UV detection at 210 nm were used. A degradation study treating the three antibiotics with 0.5 M hydrochloric acid, 0.5 M sodium hydroxide and 3% H2O2 indicated that the developed method was selective toward lincomycin, polymyxin, vancomycin and their degradation products. Other ingredients of the preservation solution, like those from the cell culture medium, did not interfere. The method was validated with good sensitivity, linearity, precision and accuracy. Furthermore, lincomycin, polymyxin and vancomycin were found to be stable in this preservation solution for 4 weeks when stored at -20 °C.

Development and validation of a simple and affordable LC-UV method for identification and assay of selected antimicrobial medicines.

Antimicrobials, particularly antibiotics, are among the most common classes of drugs reported as substandard and falsified (SF) in developing countries. Therefore, it is important to develop simple and affordable analytical methods for the quality control of antimicrobial medicines. In this study, a liquid chromatographic method with ultraviolet detection (LC-UV) was developed and validated for the screening and quantification of 13 antimicrobial medicines and one beta-lactamase inhibitor in pharmaceutical formulations. LC separation was carried out on a Kinetex C18 column (150 mm × 4.6 mm, 2.6 µm) with gradient elution. The mobile phase consisted of mixtures of acetonitrile-water-10 mM phosphate buffer pH 3.5 at ratios of 3:92:5, v/v/v for mobile phase A and 50:45:5, v/v/v for mobile phase B with a flow rate of 0.5 mL/min. The screening method was intended for confirmation of the identity of the actives and validated for specificity and robustness, whereas the quantification method (using only a different detection wavelength) was further validated in terms of linearity, accuracy, sensitivity and precision (repeatability, intermediate precision). For all compounds, the method was found to be linear (r2 > 0.999), precise (%RSD < 1%), accurate (% recovery of 98-102%), sensitive, specific and robust. The developed LC method was successfully applied for the identification and assay of 12 antimicrobial samples from Ethiopia. Among the 12 samples analyzed, one (8.3%) product was confirmed to be falsified.

A fast and efficient method for screening and evaluation of hypoglycemic ingredients of Traditional Chinese Medicine acting on PTP1B by capillary electrophoresis.

As a pivotal enzyme that regulates dephosphorylation in cell activities and participates in the insulin signaling pathway, protein tyrosine phosphatase 1B (PTP1B) is considered to be an important target for the therapy of diabetes. In this work, a rapid and efficient inhibitor screening method of PTP1B was established based on capillary electrophoresis (CE), and used for screening and evaluating the inhibition effect of Traditional Chinese Medicine on PTP1B. Response Surface Methodology was used for optimizing the conditions of analysis. After method validation, the enzyme kinetic study and inhibition test were performed. As a result, the IC50 of PTP1B inhibitors Ⅳ and ⅩⅧ were consistent with reported values measured by a conventional method. It was found that the extracts of Astragalus membranaceus (Fisch) Bunge and Morus alba L. showed prominent inhibition on the activity of PTP1B, which were stronger than the positive controls. Meanwhile, on top of the excellent advantages of CE, the whole analysis time is less than 2 min. Thus, the results demonstrated that a fast and efficient screening method was successfully developed. This method could be a powerful tool for screening inhibitors from complex systems. It can also provide an effective basis for lead compound development in drug discovery.

Impact of diluents on the calibration of direct dynamic thermal desorption prior to gas chromatography.

A thermal desorber (TD) can be used in different ways to introduce samples in a gas chromatographic (GC) system. Besides its conventional use where the collected analytes are released from the sorbent in the sample tube, direct dynamic desorption (DDD) is an interesting option where a solid sample is put directly in the TD tube. However, since no sorbent is used for the sample, proper calibration is not straightforward. This issue was investigated in the present work using offline liquid calibration (OLC) and inline liquid calibration (ILC). Unexpectedly, ILC yielded a lower response than OLC. This could be related to the adsorption kinetics of the analytes and water on the cold trap of the TD. More insight was gained performing double injection ILC experiments with toluene as diluent for the analytes and injecting water before or after the toluene solution. This revealed a clear influence of the diluent. The influence of water was further explored applying two cold trap temperatures (4 °C and -30 °C). Inserting a LiCl trap in the TD tube to capture the water was found to be an effective solution for the problem. Finally, quantitative aspects of this approach were demonstrated.