Application of near infrared spectroscopy and multivariate control charts for monitoring biodiesel blends

Multivariate control charts in conjunction with near infrared spectroscopy were developed to verify the quality of biodiesel blends (2% of biodiesel and 98% of diesel). The control charts were built using the net analyte signal method, generating three charts: the NAS chart that corresponds to the analyte of interest (biodiesel in this case), the interference chart that corresponds to the contribution of other compounds in the sample (diesel in this case) and the residual chart that corresponds to nonsystematic variations. For each chart, statistical limits were developed using samples inside the quality specifications. It was possible to identify biodiesel blend samples that were out of specifications relative to biodiesel content, biodiesel contaminated with vegetable oil and diesel contaminated with naphtha.