Thermal lens spectrometric determination of ammonium in water samples based on indophenol formation with sodium salicylate
For the first time, a thermal lens spectrometric (TLS) detection was applied for the determination of ammonium based on indophenol blue reaction. The blue–coloured indophenol was detected following excitation by a krypton laser at 647 nm. The achieved limit of detection (LOD) and limit of quantification (LOQ) were 8 ng/mL and 25 ng/mL, respectively. This represents an improvement of 20 times when compared to the spectrophotometric detection. The results obtained by TLS were benchmarked by ammonium determination using the ion exchange chromatography (IC). It was demonstrated that for the analysed samples the developed TLS method offers slightly lower LOD in comparison to IC (LOD = 12 ng/mL). The ammonium levels in all water samples determined by TLS were in good agreement with the concentrations determined by IC. A sample throughput of 12 samples per hour was provided by TLS, which is about three times higher when compared to the IC.
Keywords: ammonium detection, thermal lens spectrometry, ion chromatography, water analysis, indophenol formation, sodium salicylate