Simultaneous determination of lactic acid and pyruvic acid in tissue and cell culture media by gas chromatography after in situ derivatization-ultrasound-assisted emulsification microextraction

Enzymatic colorimetric method for turn-on determination of l-lactic acid through indicator displacement assay

l-Lactic acid is a natural α-hydroxy carboxylic acid and is commonly used as an addictive. Quantitation of l-lactic acid is indispensable in food and cosmetic industries. An enzymatic colorimetric method was developed for the determination of l-lactic acid by competitive indicator displacement assay. Boric acid inhibited the colorimetric reaction of l-3,4-dihydroxyphenylalanine (l-DOPA) catalyzed by tyrosinase. l-Lactic acid competitively displaced and released l-DOPA bound with boric acid to serve as substrate, and thus restored the tyrosinase activity. Recovery of color reaction could be spectrophotometrically determined at 475 nm and was proportional to the amount of l-lactic acid. A calibration curve between l-lactic acid concentration and recovery of absorbance were built. The concentration range of the l-lactic acid was 0.25-2.25 mM. The limit of detection (LOD) and the limit of quantification (LOQ) for l-lactic acid was estimated to be 0.05 mM and 0.16 mM, respectively. The method achieved turn-on and visual sensing with good precision, accuracy, specificity, and robustness. The assay method exhibited a promising prospect to determine the content of l-lactic acid in foods and cosmetics.

A review of bioanalytical applications of microextraction techniques combined with derivatization

Microextraction techniques have attracted the attention of many researchers working in the field of bioanalysis due to their unique advantages, mainly in downsizing the scale of sample preparation steps. In parallel, analytical derivatization offers a powerful combination in terms of additional sensitivity, selectivity and compatibility with modern separation techniques. The aim of this review is to discuss the most recent advances in bioanalytical sample preparation based on the combination of microextraction and analytical derivatization. Both innovative fundamental reports and analyte-targeted applications are included and discussed. Dispersive liquid-liquid extraction and solid-phase microextraction are the most common techniques that typically combined with derivatization, while the development of novel and greener protocols is receiving substantial consideration in the field of analytical chemistry.

A photonic crystal fiber-based fluorescence sensor for simultaneous and sensitive detection of lactic acid enantiomers

A photonic crystal fiber (PCF)–based fluorescence sensor is developed for rapid and sensitive detection of lactic acid (LA) enantiomers in serum samples. The sensor is fabricated by chemical binding dual enzymes on the inner surface of the PCF with numerous pore structures and a large specific surface area, which is suitable to be utilized as an enzymatic reaction carrier. To achieve simultaneous detection of l-LA and d-LA, the PCF with an aldehyde-activated surface is cut into two separate pieces, one of which is coated with l-LDH/GPT enzymes and the other with d-LDH/GPT enzymes. By being connected and carefully aligned to each other by a suitable sleeve tube connector, the responses of both l-LA and d-LA sensors are determined by laser-induced flourescence (LIF) detection. With the aid of enzyme-linked catalytic reactions, the proposed PCF sensor can greatly improve the sensitivity and analysis speed for the detection of LA enantiomers. The PCF sensor exhibits a low limit of detection of 9.5 μM and 0.8 μM, and a wide linear range of 25–2000 μM and 2–400 μM for l-LA and d-LA, respectively. The sensor has been successfully applied to accurate determination of LA enantiomers in human serum with satisfactory reproducibility and stability. It is indicated that the present PCF sensors would be used as an attractive analytical platform for quantitative detection of trace-amount LA enantiomers in real biological samples, and thus would play a role in disease diagnosis and clinical monitoring in point-of-care testing.

Liquid chromatography-tandem mass spectrometry analysis for identification and quantification of antimicrobial compounds in distillery wastewater

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Analyze and identify 4 levels of small molecule compounds in distillery wastewater.

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Simple method for quantification of five antimicrobial compounds.

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Column temperature affected the lactic and succinic acid chromatographs significantly.

A high-resolution mass spectrometry (HR-MS) method was developed to analyze and identify small molecule compounds in distillery wastewater. According to identification confidence levels, 4 levels of compounds were identified. The five antimicrobial compounds (lactic acid, succinic acid, acetophenone, cinnamic acid, and phenyllactic acid), which shown in high concentrations, were at the highest level of confidence (level 1, confirmed structure). Thus, a rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to simultaneously quantify these antimicrobial compounds. The analysis was performed in the selective reaction monitoring (SRM) mode via the electrospray ionization (ESI) source operating in the negative ionization mode. Linear calibration curves were obtained over the concentration range of 50–1000.0 ng/mL for succinic acid, acetophenone, cinnamic acid, phenyllactic acid, and 375–7500 ng/mL for lactic acid. Precision and recovery of the analytes were all satisfactory (relative standard deviation < 10%). The validated method was successfully applied to quantitative analysis of the five antimicrobial compounds in distillery wastewater.•

Analyze and identify 4 levels of small molecule compounds in distillery wastewater.

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Simple method for quantification of five antimicrobial compounds.

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Column temperature affected the lactic and succinic acid chromatographs significantly.

A novel ISM-SAM strategy, based on gas chromatography/mass spectrometry analysis, to compensate for matrix effects in the determination of pyruvic acid

RATIONALE

The matrix effect is tricky in gas chromatography/mass spectrometry (GC/MS) analyses. Although several methods have been proposed to solve this problem, the results were unsatisfactory. Even fewer studies have assessed the performance of corrective methods. Hence, our study focused on assessing several common corrective methods, and then proposed a new strategy to correct for the matrix effect in GC/MS analyses.

METHODS

In GC/MS analyses, the internal standard method (ISM) was employed to overcome the matrix effect during the detection of pyruvic acid (PA) in serum samples from a healthy adult female. The accuracy of the ISM was evaluated by comparing it with the standard addition method (SAM). To employ the ISM-SAM strategy, correction factors (CFs) were established by combining the ISM and the SAM based on different groups. The CFs were used to normalize data onto the results of subsequent analyses.

RESULTS

When using the ISM to detect levels of PA, a serious bias is observed, thereby affecting the conclusions reached. In contrast, more reliable data can be obtained after normalizing results by undertaking the ISM-SAM strategy. The feasibility of this strategy was verified by comparing it with the results of the SAM alone. The ISM-SAM strategy was successfully applied to quantify the PA levels in healthy people and nephrotic syndrome patients.

CONCLUSIONS

Our results indicated that a false outcome was presented when only the ISM was used to adjust the data, and important information would be missed if the correction strategy was not carried out. Therefore, ISM-SAM, as an available correction method, should be adapted to improve the reliability of research results.