Three phase liquid phase microextraction of phenylacetic acid and phenylpropionic acid from biological fluids

Analysis of 4-Hydroxyphenyllactic Acid and Other Diagnostically Important Metabolites of α-Amino Acids in Human Blood Serum Using a Validated and Sensitive Ultra-High-Pressure Liquid Chromatography-Tandem Mass Spectrometry Method

The profile of and dynamic concentration changes in tyrosine, phenylalanine, and tryptophan metabolites in blood are of great interest since they could be considered potential biomarkers of different disorders. Some aromatic metabolites, such as 4-hydroxyphenyllactic, 4-hydroxyphenylacetic, phenyllactic, and 4-hydroxybenzoic acids have previously demonstrated their diagnostic significance in critically ill patients and patients with post-COVID-19 syndrome. In this study, a sensitive method, including serum protein precipitation with methanol and ultra-high-pressure liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) detection, was developed and validated for six phenyl- and five indole-containing acids in human serum. The liquid-liquid extraction was also examined, but it demonstrated unsatisfactory results based on analyte recoveries and the matrix effect. However, the recoveries for all analytes reached 100% and matrix effects were not observed using protein precipitation. This made it possible to use deionized water as a blank matrix. The lower limits of quantitation (LLOQs) were from 0.02 to 0.25 μmol/L. The validated method was used for the analysis of serum samples of healthy volunteers (n = 48) to reveal the reference values of the target analytes. The concentrations of the most clinically significant metabolite 4-hydroxyphenyllactic acid, which were revealed using UPLC-MS/MS and a previously developed gas chromatography-mass spectrometry method, were completely comparable. The proposed UPLC-MS/MS protocol can be used in the routine clinical practice of medical centers.

Conformational equilibrium of phenylacetic acid and its halogenated analogues through theoretical studies, NMR and IR spectroscopy

This paper presents a study on the conformational preferences of phenylacetic acid (PA) and its halogenated analogues (FPA, CPA, BPA). To clarify the effects that rule these molecules' behaviour, theoretical calculations were used, for both the isolated phase and solution, combined with nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. Most conformations of phenylacetic acid and its halogenated derivatives are stabilized through the hyperconjugative effect, which rules the conformational preference. NMR analyses showed that even with the variation in medium polarity, there was no significant change in the conformation population. Infrared spectroscopy showed similar results for all compounds under study. In most spectra, two bands were found through the carbonyl deconvolution, which is in accordance with the theoretical data. It was possible to prove that variation in the nature of the substituent in the ortho position had no significant influence on the conformational equilibrium.

Three-phase hollow-fiber microextraction combined with ion-pair high-performance liquid chromatography for the simultaneous determination of five components of compound α-ketoacid tablets in human urine

The determination of α-ketoacid concentration is demanded to evaluate the absorption and metabolic behavior of compound α-ketoacid tablets taken by chronic kidney disease patients. To eliminate the interference of endogenous substance of urine and enrich the analytes, a three-phase hollow-fiber liquid-phase microextraction combined with ion-pair high-performance liquid chromatography method was established for the determination of d,l-α-hydroxymethionine calcium, d,l-α-ketoisoleucine calcium, α-ketovaline calcium, α-ketoleucine calcium, and α-ketophenylalanine calcium of compound α-ketoacid tablets in human urine samples. The extraction parameters, such as organic solvent, pH of donor phase and acceptor phase, stirring rate, and extraction time were optimized. Under the optimal conditions, the obtained enrichment factors were up to 11-, 110-, 198-, 202-, and 50-fold, respectively. The calibration curves for these analytes were linear over the range of 0.1-10 mg/L for α-ketovaline calcium, d,l-α-ketoisoleucine calcium, and α-ketoleucine calcium, 0.5-10 mg/L for d,l-α-hydroxymethionine calcium, and α-ketophenylalanine calcium with r > 0.99. The relative standard deviations (n = 5) were less than 6.27% and the LODs were 100.7, 10.0, 5.8, 7.8, and 8.6 μg/L (based on S/N = 3), respectively. Good recoveries from spiked urine samples (92-118%) were obtained. The proposed method demonstrated excellent sample clean-up and analytes enrichment to determine the five components in human urine.

Liquid-phase microextraction in bioanalytical sample preparation

Liquid-phase microextraction (LPME) emerged in the mid-to-late 1990s, facing up to the main shortcomings of the classical liquid-liquid extraction. Since its origin, this new technique has been in continuous development driven by its successful and widespread use in the analytical sciences. Its inherent properties, such as low sample volume requirement, high preconcentration factors achieved and excellent sample clean-up, make LPME a very useful technique for bioanalytical sample preparation. This review focuses on the main LPME-related techniques, predominantly single-drop microextraction and supported hollow-fiber LPME, paying particular attention to the bioanalytical applications. A general view of the essential trends, including the description of promising extraction modes and solvents, is also highlighted.

Single-drop microextraction in bioanalysis

Bioanalysis usually requires a preparation procedure for sample cleanup or preconcentration. Conventional sample preparation techniques are often time consuming and labor intensive. Among recent progress in sample preparation, single drop microextraction (SDME) is one of the most efficient techniques providing both sample cleanup and preconcentration capabilities. In SDME, analytes are extracted from a sample solution into an acceptor drop and the drop is introduced to subsequent analysis. Since the volume of the acceptor drop is 1–10 µl or less, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In this review, the basic principles of two-phase and three-phase SDME are described briefly and then recently developed modes of SDME, coupling with analytical instruments, and methods to enhance the drop stability are discussed. Recent applications of SDME to biological samples, including urine, blood and saliva, for the analysis of drugs, metal ions and biomarkers are reviewed.

Determination of sulfonamides in swine muscle after salting-out assisted liquid extraction with acetonitrile coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system prior to high-performance liquid chromatography

A salting-out assisted liquid extraction coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system combined with high-performance liquid chromatography with diode-array detection (HPLC-DAD) was developed for the extraction and determination of sulfonamides in solid tissue samples. After the homogenization of the swine muscle with acetonitrile and salt-promoted partitioning, an aliquot of 1 mL of the acetonitrile extract containing a small amount of dichloromethane (250-400 microL) was alkalinized with diethylamine. The clear organic extract obtained by centrifugation was used as a donor phase and then a small amount of water (40-55 microL) could be used as an acceptor phase to back-extract the analytes in the water/acetonitrile/dichloromethane ternary component system. In the back-extraction procedure, after mixing and centrifuging, the sedimented phase would be water and could be withdrawn easily into a microsyringe and directly injected into the HPLC system. Under the optimal conditions, recoveries were determined for swine muscle fortified at 10 ng/g and quantification was achieved by matrix-matched calibration. The calibration curves of five sulfonamides showed linearity with the coefficient of estimation above 0.998. Relative recoveries for the analytes were all from 96.5 to 109.2% with relative standard deviation of 2.7-4.0%. Preconcentration factors ranged from 16.8 to 30.6 for 1 mL of the acetonitrile extract. Limits of detection ranged from 0.2 to 1.0 ng/g.

Analysis of urinary aromatic acids by liquid chromatography tandem mass spectrometry

The separation and detection of 11 urinary aromatic acids was developed using HPLC-MS/MS. The method features a simple sample preparation involving a single-step dilution with internal standard and a rapid 8 min chromatographic separation. The accuracy was evaluated by the recovery of known spikes between 87 and 110%. Inter- and intra-assay precision (CV) was below 11% in all cases and the analytes were observed to be stable for up to 8 weeks when stored at -20 degrees C. The method was validated based upon linearity, accuracy, precision and stability and was used to establish reference intervals for children and adults.

Determination of fentanyl in biological and water samples using single-drop liquid-liquid-liquid microextraction coupled with high-performance liquid chromatography

A single-drop liquid-liquid-liquid microextraction (LLLME) method coupled with high-performance liquid chromatography (HPLC) was developed for the determination of fentanyl in biological (plasma and urine) and wastewater samples. Fentanyl is a potent synthetic narcotic analgesic administered in the form of a transdermal patch for the management of chronic pain. Fentanyl was extracted from 0.01 M NaOH solution (donor phase) into a thin layer of organic phase (100 muL), then back-extracted into 5 muL of the acidic acceptor microdrop (1 x 10(-3)M HClO(4)) immersed in the organic membrane from the tip of a 25-muL HPLC syringe. After the extraction, the microdrop was withdrawn into the syringe and injected directly into a HPLC system for analysis. The parameters influencing the extraction efficiency including the organic solvent and its volume, acceptor microdrop volume, composition of the donor and acceptor phases, stirring rate, temperature, salt addition and pre- and back-extraction times were investigated and optimized. At the most appropriate conditions (100 muL of n-octane, 3.6 mL of the donor phase maintained at 0.01 M NaOH, 5 muL of 1 x 10(-3)M HClO(4) as the acceptor microdrop, stirring rate of 1000 rpm for pre-extraction and 700 rpm for back-extraction, 30 degrees C, no salt addition, 30 min for pre-extraction and 20 min for back-extraction), an enrichment factor (EF) of 355 was obtained. The limit of detection (LOD) was 0.1 ngmL(-1) (based on S/N=3) and intra- and inter-day relative standard deviations less than 9% were obtained. The calibration graph was linear within the range of 0.5-1000 ngmL(-1) with the correlation coefficient (r) of 0.9999. Finally, the feasibility of the proposed method was evaluated by extraction and determination of fentanyl in plasma, urine and wastewater samples and satisfactory results were obtained.

Determination of tramadol in human plasma and urine samples using liquid phase microextraction with back extraction combined with high performance liquid chromatography

Liquid phase microextraction by back extraction (LPME-BE) combined with high performance liquid chromatography (HPLC)-fluorescence detection was developed for the determination of tramadol in human plasma. Tramadol was extracted from 2 mL of basic sample solution (donor phase) with pH 11.5 through a micro liter-size organic solvent phase (100 microL n-octane) for 25 min and finally into a 3.5 microL acidic aqueous acceptor microdrop with pH 2.5 suspended in the organic phase from the tip of a HPLC microsyringe needle for 15 min with the stirring rate of 1250 rpm. After extraction for a period of time, the microdrop was taken back into the syringe and injected into HPLC. Effected the experimental parameters such as the nature of the extracting solvent and its volume, sample temperature, stirring rate, volume of the acceptor phase, pH and extraction time on LPME-BE efficiency was investigated. At the optimized condition, enrichment factor of 366 and detection limit (LOD) of 0.12 microg L(-1) were obtained. The calibration curve was linear (r=0.999) in the concentration range of 0.3-130 microg L(-1). Within-day relative standard deviation RSD (S/N=3) and between-day RSD were 3.16% and 6.29%, respectively. The method was successfully applied to determine the concentration of tramadol in the plasma and urine samples and satisfactory results were obtained.