When Size Matters—Near Infrared Reflection Spectroscopy of Nanostructured Materials

Abstract

This article evaluates the applicability of near infrared (NIR) reflection spectroscopy for the physico-chemical and morphological characterisation of matter on a scale smaller than 1 micrometre (normally between 1 and 100 nanometres). The investigated materials comprise porous and non-porous silica particles, carbon based materials such as C 60 fullerenes, nano-crystalline diamond (NCD) and dendrimers, all of them having diameters and/or pore sizes in the nanometre range, respectively. In case of the silica packings and differently derivatised C 60 fullerenes, absorbance signals could be clearly assigned to corresponding surface modifications. Identification or classification of the material can be achieved successfully by principal component analysis. Nano crystalline diamond surfaces, whether H-or O-terminated, could be differentiated by a computed partial least squares (PLS) regression model with around 80% precision. Generations 0-7 of poly(amidoamine) (PAMAM) dendrimers with functionalised surface amine groups are characterised in respect of particle diameter and molecular weight. The established PLS models showed a standard error of prediction of only 0.43 nm and 12.30 kDa, respectively. NIR spectroscopy has developed as a flexible analytical method that can be utilized for fast, reliable and highly reproducible screening of matter even in the nanometer range.

Celebrating the 20th Anniversary of NIR Spectroscopy at the University of Innsbruck, Austria: Contributions to material-, bio-, medicinal plant and food analysis

“…Compared to the reference method, which enables the determination of the individual parameters with a relative standard deviation between 6 and 28%, the NIR method shows RSD% between only 0.010 and 13.7%, which means a fundamental improvement in precision. 9,10…”

Online Process Control of a Pharmaceutical Intermediate in a Fluidized-Bed Drier Environment Using Near-Infrared Spectroscopy

“…Near-infrared spectroscopy (NIRS) has become a popular process control tool with a broad range of applications for precise material characterization. This fast and noninvasive technique reveals a high content of information by exciting overtone and combination vibrations in the irradiated substance, allowing for the assessment of physical and chemical sample characteristics at the same time. − Multivariate data evaluation methods , can be used to investigate the relation of spectral data from different wavelength regions in one context to extract the highest degree of information . With an appropriate sampling system, the sample compositions can be determined nondestructively directly in the production area during manufacturing − with various in-, at-, or online configurations. , The diverse applications so far cover the primary production of pharmaceutical substances (reaction monitoring of crystallization and distillation processes and identification of polymorph forms) as well as secondary production (final drug machining including milling, granulation, drying, blending, compression, and coating). − …”