Direct Determination of Rosmarinic Acid in Lamiaceae Herbs Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Chemometrics

For the determination of rosmarinic acid (RA) directly in pulverized plant material, a method is developed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) without any physicochemical pretreatment of samples. The RA content of 11 samples of eight different Lamiaceae herbs, as determined by high performance liquid chromatography (HPLC), varied between 86 +/- 1 mg/g (in lemon balm) and 12.0 +/- 0.8 mg/g (in hyssop) of dried plant material. The 11 samples and 50 other additional samples, which were prepared by mixing initial samples with KBr, were measured using DRIFTS. The second derivative of the spectral region 1344-806 cm(-1) was used and the corresponding data were analyzed using partial least squares (PLS) regression. The correlation between infrared spectral analysis and HPLC measurements shows that the DRIFTS method is sufficiently accurate, simple, and rapid. The RA content of the 11 Lamiaceae samples determined by DRIFTS ranged from 81 +/- 4 mg/g (in lemon balm) to 12 +/- 3 mg/g (in hyssop) of dried plant material.