Quantification of Overlapped Peaks with Partial Least Squares Regression : Open Tubular Ion Chromatography for Sodium and Ammonium Ions

We propose an approach for the simultaneous determination of multiple component (i.e., Na+ and NH4+) solutions based on open tubular ion chromatography (OTIC) coupled with chemometrics. The sample solutions containing Na+ and NH4+ (0 – 500 μM) were prepared at various concentration ratios. The samples were analyzed by OTIC within the time range of t = 0 – 18.0 min. The partial least squares (PLS) regression method was applied to the acquired chromatograms in order to predict ionic concentrations. The constructed PLS regression models were able to predict Na+ and NH4+ concentrations. The regression vectors of the Na+ and NH4+ prediction models yielded positive peaks at 11.8 min and 13.3 min, respectively. The determination coefficient between predicted and measured cation concentration were respectively 0.9187 for Na+ and 0.9314 for NH4+. The combination of the OTIC and PLS regression methods was useful for the determination of ionic concentrations under unresolved chromatogram peak conditions.