Alcohol Determination by HPLC with Postcolumn Derivatization Based on the Thiosulfate-catalyzed Reaction of Alcohols and Cerium(IV) and Fluorescence Detection of Cerium(III)

Background: Determination of a reducing substance based on the reaction between Ce(IV) and a reducing substance and fluorescence detection of Ce(III) generated has been reported as a selective and sensitive method. However, this method could not be applied to the determination of alcohol due to the low reaction rate of alcohol and Ce(IV). Objective: We found that thiosulfate catalytically enhanced reaction of alcohols (such as, methanol, ethanol, and propanol) and Ce(IV). Utilizing this effect, we developed a new method for the determination of alcohols. Results: In the presence of thiosulfate, an increase in fluorescence intensity was detected by injecting alcohol at concentrations of several millimolar, whereas it was not observed even at the concentration of 10% v/v (2 M for ethanol) in the absence of thiosulfate. The optimum detection conditions were determined to be 4.0 mM Ce(IV) sulfate and 0.50 mM thiosulfate, and the detection limit (S/N = 3) of ethanol under these conditions was 1 mM. In the calibration curves, changes in the slope were observed when the alcohol concentrations were approximately 10–25 mM. Using a thiosulfate solution containing ethanol as the reaction solution, a calibration curve without any change in slope was obtained, although the concentration of ethanol at the detection limit increased. The alcohols in the liquor and fuel were successfully analyzed using the proposed detection method as a postcolumn reaction. Conclusion: This new alcohol detection method using a versatile fluorescence detector can be applied to the postcolumn reaction of HPLC omitting need of time-consuming pretreatment processes.

Existing problems and ways of their solution in the analysis of amino acid composition

For obtain accurate aminoacids analysis results for peptide samples it is need to pay attention for method of analysis and method of sample preparation. Now some samplpreparation methods are known: acid and basic hydrolysis. In this article the comparison of two methods of aminoacids analysis were observed: pre-column or post-column derivatization. Analysis of lysine in lysine sulphate was studied, results were compared with control samples. For pre-column derivatization o-phthalic anhydride was used, and for post-column derivatization ninhydrin reagent was used. In experimental part advantages of post-column derivatization was shown and more accurate results were obtained. Chromatographic separation, derivatization and detection were carried out on aminoacids analisators Hitachi (Japan) и Sykam (Germany). Samplepreparation methods were observed on valine and threonine analysis using postcolumn derivatization with ninhydrin reagent. The effect of pH adjustment after acid hydrolysis was studied. Basic solution addition best results in comparison with sample evaporation and reconstitution were shown. For final sample analysis optimal methods of analysis and samplepreparation were chosen. Results were compared with results of European Accredited Laboratory.

Analysis of Theanine in Tea (Camellia sinensis) Dietary Ingredients and Supplements by High-Performance Liquid Chromatography with Postcolumn Derivatization: Single-Laboratory Validation, First Action 2016.10

An HPLC method with postcolumn derivatization was developed and validated for the determination of theanine content in tea dietary ingredients and supplements. A variety of common commercially available supplement forms such as powders, liquid tinctures, tablets, softgels, and gelcaps, as well as three National Institute of Standards and Technology Camellia sinensis Standard Reference Materials were investigated in the study. A simple extraction procedure using citrate buffer at pH 2.2 allowed for the analysis of theanine without additional cleanup or concentration steps, even at low ppm levels. Theanine was separated from other naturally occurring amino acids using a cation-exchange column and detected using a UV-Vis detector after derivatization with ninhydrin reagent. A single-laboratory validation demonstrated that specificity, accuracy, precision, and other method performance parameters have met the requirements set for theanine analysis by the AOAC Stakeholder Panel on Dietary Supplements.

Aflatoxins in Brazilian Peanut Confection

The study's objectives were to evaluate a method for the determination of aflatoxins (AFs) in the Brazilian peanut confection “Paçoca” and to apply the method in investigating AF concentrations in Paçoca marketed in São Paulo State throughout 2013. Results of another survey conducted between 1994 and 2002 with another method were also reported. The current method consists of immunoaffinity column cleanup, LC with postcolumn derivatization for AF fluorescence enhancement, and fluorescence determination for the toxins. The mean recovery and mean RSDr values were 88.6 and 7.9%, respectively. The LODs for aflatoxin B1, aflatoxin B2, aflatoxin G1, and aflatoxin G2 were 0.04, 0.01, 0.02, and 0.01 ng/g; and the LOQs were 0.15, 0.04, 0.07, and 0.04 ng/g, respectively. Results of the two survey studies indicate that the contamination of AFs in Paçoca remains a public health problem. In the 2013 survey, 71 of 100 samples (71%) had AFs contamination ranging from 0.3 to 41.8 ng/g, with 12 samples (12%) containing >20 ng/g of the toxins, whereas in the 1994–2002 survey, 73 of 150 samples (51%) had AFs contamination ranging from 9 to 1439 ng/g with 65 samples (45%) containing levels >20 ng/g.