Novel Determination of Organic Acids in Diesel and Motor Oil by Ion Chromatography

Annual hypoxia causing long-term seawater acidification: Evidence from low-molecular-weight organic acids in the Changjiang Estuary and its adjacent sea area

In this study, components, concentrations, distribution characteristics, sources of low-molecular-weight organic acids (LMWOAs) and relationships among the annual hypoxia, LMWOAs and seawater acidification were investigated in the Changjiang Estuary and its adjacent sea area in July 2015. Lactic, acetic and formic acids were detected in the seawater samples in the study area, and their total concentrations (ΣLMWOAs) varied from 0 to 262.6 μmol·L^-1, with an average value of 39.2 μmol·L^-1. In the surface seawater, high concentration areas of ΣLMWOAs occurred in the sea area near the Changjiang Estuary and the Hangzhou Bay, and north of study area. In the sampling stations along transect A6, high concentration areas of ΣLMWOAs appeared in the bottom seawater of nearshore stations and middle seawater of offshore stations. The terrigenous inputs, especially the Changjiang runoff, were the dominant sources for LMWOAs in the sampling period. The consistency of hypoxia areas, high concentration areas of ΣLMWOAs and low pH value areas in winter and summer suggested that annual hypoxia could cause the long-term seawater acidification by producing LMWOAs in the Changjiang Estuary and its adjacent sea area.

High-Performance Sensing of Formic Acid Vapor Enabled by a Newly Developed Nanofilm-Based Fluorescent Sensor

Although it is widely used in industry and food products, formic acid can be dangerous owing to its corrosive properties. Accurate determination of formic acid would not only benefit its qualified uses but also be an effective way to avoid corrosion or injury from inhalation, swallowing, or touching. Herein, we present a nanofilm-based fluorescent sensor for formic acid vapor detection with a wide response range, fast response speed, and high sensitivity and selectivity. The nanofilm was synthesized at a humid air/dimethyl sulfoxide (DMSO) interface through dynamic covalent condensation between two typically designed building blocks, de-tert-butyl calix[4]arene-tetrahydrazide (CATH) and 4,4',4″,4‴-(ethene-1,1,2,2-tetrayl)tetra-benzaldehyde (ETBA). The as-prepared nanofilm is uniform, flexible, fluorescent, and photochemically stable. The thickness and fluorescence intensity of the nanofilm can be facilely adjusted by varying the concentration of the building blocks and the sensing performance of the nanofilm can be optimized accordingly. Based on the nanofilm, a fluorescent sensor with a wide response range (4.4 ppt-4400 ppm) for real-time and online detection of formic acid vapor was built. With the sensor, a trace amount (0.01%) of formic acid in petroleum ether (60-90 °C) can be detected within 3 s. Besides, fluorescence quenching of the nanofilm by formic acid vapor can be visualized. It is believed that the sensor based on the nanofilm would find real-life applications in corrosion and injury prevention from formic acid.

Progress in pretreatment and analysis of organic Acids: An update since 2010

Organic acids, as an important component of food, have great influence on the flavor, texture, freshness of food. By lowering the pH of food to bacteriostatic acidity, organic acids are also used as additives and preservatives. Because organic acids are crucial to predict and evaluate food maturity, production and quality control, the rapid and sensitive determination methods of organic acids are necessary. This review aims to summarize and update the progress of the determination of organic acids in food samples. Pretreatment methods include simple steps (e.g., "dilute and shoot," protein precipitation, filtration, and centrifugation) and advanced microextraction methods (e.g., hollow fiber liquid phase microextraction, stir bar sorptive extraction and dispersive micro-solid phase extraction). Advances in novel materials (nanomaterial), solvents (ionic liquids and supercritical fluids) and hybrid methods are clearly displayed in detail. Continuous progress which has been made in electrochemical method, two-dimensional chromatography, high resolution mass is thoroughly illustrated.

Impurity analysis of 2-butynoic acid by ion chromatography-mass spectrometry

Small organic acids are widely used within the pharmaceutical industry but can be difficult to analyse. Ion chromatography is a suitable technique for the analysis of these acids but method development can be hindered as mass spectrometry is not often used as a detector; this means that peak tracking and peak purity cannot be performed. The authors report method development for the analysis of 2-butynoic acid, where by using electrospray ionisation mass spectrometry, peak purity was investigated and the presence of co-eluting impurities determined. Optimisation of the additives in the make-up flow to the mass spectrometer was shown to have an impact on the response observed. A standard series of organic acids were analysed spiked in to 2-butynoic acid at levels representative of impurities, the presence of the 2-butynoic acid did not impact the linearity or limit of detection observed for the acids; R² values greater than 0.98 were obtained for all acids with and without the presence of 2-butynoic acid with a limit of detection at 1 ppb for all but one of the acids.