Detection Methods for Organic Acids

Organic acids are commonly found in fruits in natural plants and are most abundant in fruits, such as green plums and ginkgo biloba. In the fruit is mainly malic acid and tartaric acid and some other fruit acids, which are also the most important source of acidity. The acidity in organic acids also neutralizes the sweetness in them very well, forming a special flavor. The organic acids in the leaves and fruits of the plant combine together to participate in photosynthesis and respiration, as well as in the metabolic process of synthesizing esters. In the field of cosmetics there are also great effects, such as in skin care products, amino acid moisturizers of organic acids have moisturizing, skin softening, anti-wrinkle, whitening, refreshing and other effects. Organic acids can also be found in biological tissues and are characterized by high purity, ease of use and good stability.

Most organic acids present similar structures with similar spectral properties and pKa values, so they have similar chromatographic behaviors. Moreover, the content of organic acid phytohormones is low, so the separation and quantification are difficult. Traditional detection techniques and analytical methods are more difficult to achieve the analysis of organic acid phytohormones.

In recent years, various researchers have devoted themselves to the research of various new analytical methods and techniques that are highly efficient, rapid and sensitive. The inherent high sensitivity and selectivity of high-performance liquid chromatography-mass spectrometry (HPLC-MS) has become the most prominent and widely used technique for the analysis of organic acids.

Short chain organic acids determinations (Mortera et al., 2018)

HPLC-MS offers low detection limits, but this is dependent on the ionization efficiency of the ESI. One way to achieve low detection limits is to concentrate the analytes to be measured in the sample, but this is usually not feasible due to interference from matrix components or too low sample levels. The analytical performance of HPLC-MS can be improved by improvements in instrument design, but the improvement in analytical performance can also be obtained by optimizing the improved chromatographic performance.

Chemical derivatization techniques have been shown to be a powerful strategy to improve the performance of chromatography and can enhance the detection efficiency of compounds. Derivatization is a specific chemical reaction by which a specific target compound is attached to a particular moiety so that it is transformed into a new compound with new physical and chemical properties such as boiling point, spectroscopic properties, ionization efficiency, etc. The derivatives are then subjected to liquid chromatography-mass spectrometry (LC-MS) analysis and qualitative and quantitative analysis for the purpose of indirect qualitative and quantitative analysis of the analyte.

The selection of the reactive functional groups in the target compound and the reactive groups of the derivatization reagents is a prerequisite for derivatization. Derivatization reagents can react with substances containing different functional groups, including carbonyl, hydroxyl, carboxyl, amine and thiol. Organic acid phytohormones are very polar and have a simple structure, so they need to be derivatized and then analyzed by HPLC-MS.

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Reference

1. Mortera, P., Zuljan, F. A., Magni, C., et al. (2018). Multivariate analysis of organic acids in fermented food from reversed-phase high-performance liquid chromatography data. Talanta, 178, 15-23.

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