Indirect K⁺ Ions Determination from Infrared Spectra of Biological Samples Owing to Their Interactions with Biomolecules

Abstract

Complex-formation between carbohydrates and cations may have important biological implications. Potassium ions and sucrose interactions have been observed by the examination of the spectral patterns obtained by multi-dimensionnal analysis (Principal Component Analysis) applied to infrared spectra of biological samples. Several authors have extensively studied ions-sugars interactions particularly calcium and magnesium-sugar interactions and have shown that these interactions induced shifts and splitting in infrared absorption bands.

We here report to use Principal Component Analysis and Principal Component Regression for the quantitative determination of K⁺ ions in biological solutions by investigating interactions between this cation and sucrose molecules. The spectral pattern that describes the principal component (axis 1), features absorption peaks at 925, 997, 1053, 1112 and 1136 cm-1 that are characteristic of sucrose. The correlation coefficient between axis 1, representative of pure sucrose, and the values of potassium concentrations is 0. 5213. The spectral pattern of the second axis is also associated with the sucrose pattern. The shifts and splittings of the absorption bands that are observed in this second spectral pattern are associated with potassium-sucrose interactions. The correlation coefficient between this second axis (axis 3) and the K⁺ concentration is equal to 0. 2152. Most of the information relative to potassium ions are contained in this axis. These informations appear as interactions between sucrose and the cation. With the first two axes, the correlation coefficient reaches 0. 7365 and this opens the possibility of quantifying K⁺ in biological samples. The other axes improved the correlation coefficient, which reached 0.9945 with the first ten axes. For the predicted concentrations of K⁺, the bias and standard deviation values, 8 × 10-2 and 0.43 respectively, showed that the predicted values are very close to those determined by flame photometry.

Hence, even if K⁺ cation does not have a Mid-infrared spectral fingerprint, interactions between K⁺ and sucrose in raw sugar cane juices allow the indirect quantitative determination of this ion.

Key Words:

• K⁺ determination
• ion-sugar interactions
• Mid-FTIR
• multivariate analysis