Tetsuo Fuse

A review of a new voltammetric method for determining acids

A new method for determining acids based on the voltammetric reduction of quinone was developed with the objective of providing a sensitive and rapid means for acid assay superior to the conventional titration method. An assessment of this method was made for determining the free fatty acid content in fats and oils, the total acidity of beverages, and the esterase activity to demonstrate its usefulness for a wide range of applications.

Determination of higher fatty acids in oils by high-performance liquid chromatography with electrochemical detection

Abstract A system of high-performance liquid chromatography with electrochemical detection was developed for the separation and determination of higher fatty acids. An octadecylsilica (ODS) column was used as the stationary phase and an ethanol–acetonitrile (10:90) mixture as the mobile phase. The eluate was mixed with a quinone solution which was composed of 6 m M 2-methyl-1,4-naphthoquinone and 76 m M LiClO 4 in ethanol–acetonitrile (10:90) through a mixing coil. Peak height for higher fatty acids measured at −415 mV vs. saturated calomel electrode (SCE) was linear against the amount of acid between 20 and 1200 pmol. Free fatty acids in various oil samples were determined by this method, which was found not only sensitive and reproducible but also a simple means for separating and determining free fatty acids in oils.

Determination of acid values of fats and oils by flow injection analysis with electrochemical detection

A new method using a flow injection system with electrochemical detection was developed to determine acid values of fats and oils. VK3 (2-methyl-1,4-naphthoquinone) solution, i.e., ethanol containing 3 mM VK3 and 38 mM LiClO4, was used as the carrier solution. Flow signals were monitored at -0.33 V vs. Ag/AgCl. For preparation of a sample solution, an oil sample was completely dissolved in VK3 solution, or fatty acids were extracted from the sample into this solution. Aliquots (5 microliters) of the sample solution were injected into the flow injection system. Acid values were determined based on flow signals for 14 samples and the results were found to be consistent with those by potentiometric titration. Relative standard deviation was less than 2%. Samples were processed at the rate of 60 h-1. The stability of fish and cod liver oils was followed by measuring acid values for 8 weeks. This method proved to be a simple and rapid means for acid value determination.

Electrochemical detection in flow injection analysis for determining serum lipase activity

Abstract As a simple and rapid method for serum lipase determination, assessment was made of electrochemical detection in flow injection analysis (FIA), by measuring the voltammetric prepeak accompanied by the reduction of 2-methyl-1, 4-naphthoquinone (vitamin K 3 , VK 3 ) due to the effect of free fatty acids. A sample containing lipase was incubated with olive oil as the substrate at 37 °C for 10 min to bring about the release of fatty acids. The sample solution was prepared by dissolving the oily residue extracted by ether in ethanol solution containing 3 mM VK 3 and 38 mM LiCIO 4 . A 5 μl aliquot of the sample solution was injected into the flow injection (FI) system. The peak height of the flow signal was linear to lipase activity between 10 and 1000 U l −1 and RSD was 1.2% for 70 U l −1 ( n = 5). By this method, as many as 30 samples h −1 can be processed, thus showing this method to be useful and highly efficient.

Electrochemical determination of lipase activity in pharmaceutical preparations

Abstract Flow injection analysis with electrochemical detection was used for lipase assay in pharmaceutical preparations. The method is based on the fact that the current of voltammetric prepeak, accompanied by the reduction of 2-methyl-1,4-naphthoquinone (vitamin K 3 , VK 3 ) due to the effects of fatty acids, is proportional to the acid concentration. A sample solution containing lipase was incubated with olive oil (substrate) at 37°C with stirring for 15 min, and the released fatty acids were extracted by ether. No emulsifying agent was needed in the incubation of the enzyme reaction mixture. An acid test solution prepared by dissolving the extracts in ethanol containing 3 mM VK 3 and 38 mM LiClO 4 (the same composition as the carrier solution) was injected into the flow injection system. The flow signal was linear to the lipase activity ranging from 10 to 1500 U/l for sample solutions obtained from the digestive preparations. By this method, analysis of the fat digestive power of the commercially available preparations could be accomplished with good results, thus showing this method to be practically useful.