I am using fatty acid, alcohol as a reactant and lipase as a biocatalyst for ester production. Is there any other technique for fatty acid detection except titration and HPLC.
Yes you can esterify it and once the sample gets vaporizable you can use GC for their detection and quantification on development of calibration curve. Develop a right method for it. Since fatty acids are long chain compounds you may have to use a solvent like tetrahydrofuran or so for the preparation of solution of the sample in spectrphotometry. Most importantly in both the above methods you require standards in the form of each of the free acids in pure form. However I would prescribe GC preferentially over spectroohotometry.