Characterization of Alginates by Nuclear Magnetic Resonance (NMR) and Vibrational Spectroscopy (IR, NIR, Raman) in Combination with Chemometrics
This chapter describes three different spectroscopic methods for structural characterization of the commercial important hydrocolloid alginate extracted from brown seaweed. The “golden” reference method for characterization of the alginate structure is 1H liquid-state NMR of depolymerized alginate polymers using a stepwise hydrolysis. Having implemented this method, predictive and rapid non-destructive methods using vibrational spectroscopy and chemometrics can be developed. These methods can predict the M/G-ratio of the intact alginate powder with at least the same precision and accuracy as the reference method in a fraction of the time that is required to measure the alginate using the reference method. The chapter also demonstrates how solid-state 13C CP/MAS NMR can be used to determine the M/G ratio on the intact sample by the use of multivariate chemometrics and how this method shares the characteristics of the solid-state non-destructive IR method rather than its liquid-state counterpart.
Key words13C CP/MAS NMR spectroscopy Chemometrics 1H NMR spectroscopy Infrared spectroscopy IR Multivariate curve resolution MCR Partial hydrolysis Partial least squares regression PLSR Sodium alginate
The work has been supported by a grant to Tina Salomonsen for an Industrial Ph.D. and by a grant from the strategic research council to the MicroPAT project under the InSPIRe (Danish Industry-Science Partnership for Innovation and Research in Food Science) consortium. The Faculty of Science and The Ministry of Science and Technology is acknowledged for a grant to the NMR metabolomics infrastructure.
- 2.ASTM (2012) Active standard ASTM F2259, p 5Google Scholar
- 5.Salomonsen T, Jensen HM, Larsen FH et al (2009) The quantitative impact of water suppression on NMR spectra for compositional analysis of alginates. In: Guðjónsdóttir M, Belton P, Webb G (eds) Magnetic resonance in food science. Royal Society of Chemistry, London, pp 12–19. doi: 10.1039/9781847559494-00012
- 18.Nørgaard L, Saudland A, Wagner J et al (2000) Interval partial least squares regression (i PLS): a comparative chemometric study with an example from the near infrared spectroscopy. Appl Spectrosc 54:413–419. doi: 10.1366/0003702001949500
- 20.Engelsen SB, Savorani F, Rasmussen MA (2013) Chemometric exploration of quantitative NMR data. eMagRes 2:267–278. doi: 10.1002/9780470034590.emrstm1304
- 21.Martens H, Nielsen JP, Engelsen SB (2003) Light scattering and light absorbance separated by extended multiplicative signal correction. Application to near-infrared transmission analysis of powder mixtures. Anal Chem 75:394–404. doi: 10.1021/ac020194w