Studies on the UV spectrum of poly(γ-glutamic acid) based on development of a simple quantitative method

A simple and valid ultraviolet (UV) spectrophotometric method for the determination of poly(γ-glutamic acid) is developed. The method is based on the UV absorption spectrum of γ-PGA in aqueous solution, which exhibits a maximum absorption wavelength at 216 nm. The results obtained were comparable to those obtained with the reported high-performance liquid chromatography (HPLC) method according to ICH guidelines. Under the proposed procedure, the calibration graph is linear over the range of 20-200 μg/ml with regression correlation coefficient of 0.9997. Precision (%R.S.D.<1.50) and recovery (%R.>99.29%) are good. The limit of detection (LOD) and limit of quantitation (LOQ) are 0.39 and 1.19 μg/ml, respectively. These results agree well with those of HPLC method. Its spectrum properties studies showed that the spectrum of γ-PGA remarkably changed with an increase in temperature due to γ-PGA was digested into glutamate monomer. In spite of this, the determining procedure could carried out in a wide temperature range (25-50°C). In addition, the method is not influenced by the molecular weight, but the measurement system need to control in pH 3.0-10.0 and ionic strength not more than 0.5M. The proposed method is applied successfully for high-throughput quantification of poly(γ-glutamic acid) in biological samples. The advantages of the UV method are simplicity of operation, rapidity, sensitive, low-cost and high-throughput.