Development of ion chromatography methods for the determination of trace anions in ultra pure water from power plants

Spatial variations in the distribution of trace ionic impurities in the water-steam cycle in a thermal power plant based on a multivariate statistical approach

Abstract In this study, a multivariate statistical approach was used to identify the key variables responsible for process water quality in a power plant. The ion species that could cause corrosion in one of the major thermal power plants (TPP) in Serbia were monitored. A suppressed ion chromatographic (IC) method for the determination of the target anions and cations at trace levels was applied. In addition, some metals important for corrosion, i.e., copper and iron, were also analysed by the graphite furnace atomic absorption spectrophotometric (GFAAS) method. The control parameters, i.e., pH, dissolved oxygen and silica, were measured on-line. The analysis of a series of representative samples from the TPP Nikola Tesla, collected in different plant operation modes, was performed. Every day laboratory and on-line analysis provides a large number of data in relation to the quality of water in the water-steam cycle (WSC) which should be evaluated and processed. The goal of this investigation was to apply multivariate statistical techniques and choose the most applicable technique for this case. Factor analysis (FA), especially principal component analysis (PCA) and cluster analysis (CA) were investigated. These methods were applied for the evaluation of the spatial/temporal variations of process water and for the estimation of 13 quality parameters which were monitored at 11 locations in the WSC in different working conditions during a twelve month period. It was concluded that PCA was the most useful method for identifying functional relations between the elements. After data reduction, four main factors controlling the variability were identified. Hierarchical cluster analysis (HCA) was applied for sample differentiation according to the sample location and working mode of the TPP. On the basis of this research, the new design of an optimal monitoring strategy for future analysis was proposed with a reduced number of measured parameters and with reduced frequency of their measurements. Graphical abstract

Fluoride and silver concentrations of silver diammine fluoride solutions for dental use

OBJECTIVE

To determine the short-term stability of free fluoride ion concentrations and acidity (pH values) of three commercially available SDF solutions over time.

METHODS

Three SDF products for caries control were studied: Cariestop-12%, Cariestop-30% and Saforide-38%. Their expected fluoride ion concentrations were 14,200, 35,400 and 44,800 ppm, respectively. The fluoride ion concentrations were determined with an ion-selective electrode. The acidity was determined with a pH electrode. The measurements were performed when open and at 7 and 28 days.

RESULTS

The mean fluoride ion concentrations of the freshly opened bottles were 12,525 ± 450, 13,200 ± 2060 and 55,800 ± 2536 ppm, respectively. The mean pH values were 9.4 ± 0.1, 10.4 ± 0.1 and 10.2 ± 0.2, respectively. No significant change (P > 0.05) in the fluoride ion concentrations or the acidity was detected after 7 or 28 days.

CONCLUSION

The three SDF tested solutions were alkaline. The fluoride ion concentrations of Cariestop-30% and Saforide-38% were considerably different. The fluoride ion concentrations and acidity of the products demonstrated a short-term stability over 28 days.

Determination of inorganic anions in papermaking waters by ion chromatography

A suppressed ion chromatography (IC) method for the determination of inorganic anions in process water from paperboard production was developed and validated. Common inorganic anions (Cl-, NO-3, PO 3-4 and SO2-4) were detected in fresh and process water samples collected from a paperboard production system at 16 characteristic points. It was shown that the use of an IonPac?-AS14 column under isocratic conditions with Na2CO3/NaHCO3 as the eluent and a suppression device proved to be a reliable analytical solution for the separation of the inorganic anions present in papermaking waters. This IC method is quite satisfactory concerning selectivity and sensitivity, and enables the determination of several inorganic anions over a wide concentration range. According to the obtained results, the total amount of analyzed inorganic anions was below 0.1 g/L, i.e., below the critical value which may trigger operational problems in paper production.