A method for measuring potency of narasin extracts using near-IR spectroscopy

We present a method for extracting the active component from granulated narasin samples using chloroform with subsequent quantitation by near-infrared absorption spectroscopy (NIRS). A multiple linear regression (MLR) calibration equation was developed using a set of 41 calibration samples. The potencies obtained using NIR analysis exhibit no larger than an 8% (3.03 mg/g) error when compared to results based on the primary HPLC reference method. We estimate the detection limit using this method to be 400 ppm narasin (20 mg/g potency), and the standard deviation for five independent extractions of the same sample is approximately 24 ppm (approximately 1.2 mg/g potency or approximately 1%). We also present the results from a robustness study based upon a full factorial experimental design in which we varied extraction and measurement parameters. This study indicates that sample mass causes the most variation in the results. Bottle-to-bottle variations in the chloroform used for the extraction also proved significant. Variations in sample batch, number of spectral scans, and the interactions between sample hatch*soneration time, no. Scans*time in NIR, and sample batch*sample mass were borderline significant.