In the cotton industry the most important parameters for quality of seed cotton (unginned, harvested cotton) are moisture content and impurity level. In Spain, these quality parameters are regulated and cotton producers are awarded incentives. This study was performed to investigate the potential of near infrared (NIR) spectroscopy for determining moisture content and impurity level of seed cotton. A total of 100 cotton samples collected from eight cotton ginners were used. Two spectrometers were employed, one a research level instrument (Foss NIRSystems 6500), the other with a reduced wavelength range more suitable for use at-line (InfraXact Lab). Moisture content was measured using a moisture meter, which is used in cotton industry, and by a drying oven technique. Impurity level was determined by gravimetric analysis. Partial least square regression and classification were performed for moisture and impurity level of cotton, respectively. In sample preparation, the NIRSystems 6500 with a back cover of the sample cell was better in repeatability of spectra than the InfraXact Lab with no back cover. For moisture, the best calibration was developed by using the reference values from the oven drying method and using the first derivative and standard normal variate and detrending as pre-processing of the spectral data, giving a standard error of 0.44% in the range of 5.83–14.96% moisture content. The classification model for the impurity level was developed with a combination of first derivative and multiplicative scatter correction of the spectral data and resulted in an accuracy of 80%. For both moisture and impurity parameters, using the NIRSystems 6500 instrument gave slightly better results than using the InfraXact Lab.

Keywords: cotton, quality control, near infrared spectroscopy, moisture content, impurity levels