Micro near infrared spectroscopy (MicroNIRS) based on on-line enrichment: Determination of trace copper in water using glycidyl methacrylate-based monolithic material

A micro near infrared spectroscopy (MicroNIRS) technique based on monolithic column enrichment has been developed to detect low concentration metallic ions in water. Glycidyl methacrylate–ethylene dimethacrylate–iminodiacetic acid (GMA–EDMA–IDA) monolithic material was synthesized to construct an enrichment device, which can enrich metallic ions more efficiently than chelating resin materials such as D401. Cu2+ solutions passed through the enrichment device and concentrated on the surface of the material, and then diffuse reflection NIR (DRNIR) spectra were measured by touching the NIR probe on the surface. The spectra were pretreated with multiplicative scatter correction (MSC) and the MSC-pretreated spectra showed high linear correlation to the Cu2+ concentrations in spectral regions of 900–1350 nm, 1420–1480 nm and 1970–2050 nm for all concentration ranges. PLS models built with leave-one-out cross-validation also yielded good features. The mean relative error (MRE) of prediction was 10.0% in the 0.0001–0.0010 μg mL−1 range. The concentration has low to ppb-level, but the MRE was not more than 10%, which was acceptable for trace analysis. The results revealed that the MicroNIRS technique enhanced the sensitivity of NIRS dramatically and widened the NIRS technique to micro and trace analysis field.