ABSTRACT
Since near-infrared spectroscopy (NIRS) is used in gas, liquid, and solid samples, reference standards need to come in all three forms. In addition, the nature of NIRS is that it is mainly used for complex samples (food, textiles, medicines, detergent mixes). As a consequence, it is used in both transmission and reflection modes. The majority of Standard Reference Materials (SRMs) are based on diffuse reflection and “normal” and diffuse transmission. An aspect of standards that are used in regulatory environment is that an expiration date has to be established for all standards (Standard Reference Materials or SRMs). Some standards may be very stable and durable, while others may break down chemically or from ambient UV radiation, may get contaminated or scratched during repeated use. This is why standards need to be recertified from time to time, preferably at intervals scientifically established by the end user or by intervals recommended by the manufacturer.
