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Molecules 2012, 17(6), 7440-7450; doi:10.3390/molecules17067440

NIR Spectroscopic Properties of Aqueous Acids Solutions

1,* , 1
1 School of Distance Education, Universiti Sains Malaysia, 11800 Penang, Malaysia 2 School of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia
* Author to whom correspondence should be addressed.
Received: 30 April 2012 / Revised: 27 May 2012 / Accepted: 7 June 2012 / Published: 15 June 2012
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Acid content is one of the important quality attributes in determining the maturity index of agricultural product, particularly fruits. Despite the fact that much research on the measurement of acidity in fruits through non-destructive spectroscopy analysis at NIR wavelengths between 700 to 1,000 nm has been conducted, the same response towards individual acids is not well known. This paper presents NIR spectroscopy analysis on aqueous citric, tartaric, malic and oxalic solutions through quantitative analysis by selecting a set of wavelengths that can best be used to measure the pH of the solutions. The aquaphotomics study of the acid solutions has generated R2 above 0.9 for the measurement of all acids. The most important wavelengths for pH are located at 918–925 nm and 990–996 nm, while at 975 nm for water.
Keywords: citric acid; malic acid; NIR; oxalic acid; pH; tartaric acid citric acid; malic acid; NIR; oxalic acid; pH; tartaric acid
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Omar, A.F.; Atan, H.; MatJafri, M.Z. NIR Spectroscopic Properties of Aqueous Acids Solutions. Molecules 2012, 17, 7440-7450.

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