This paper compares two ion-chromatography (IC) methods for the analysis of phosphate-based scale inhibitors in oil field brines. Both methods use an anion-exchange column with a nitric acid mobile phase for component separation, followed by mixing with a post-column reagent (PCR). In one method the PCR is an acidic ferric salt solution; the iron-scale inhibitor interaction allows UV detection. The second method uses a PCR containing a strongly fluorescent aluminum-morin complex; elution of a scale inhibitor is detected by a decrease of fluorescence due to the inhibitor complexing some of the aluminum.

These IC methods work only in fresh water, but most salt interferences (especially chloride) may be eliminated by pretreatment through a disposable cartridge containing a resin impregnated with silver. By including a concentrator column, some scale inhibitors can be quantified even at sub ppm levels in saline water.

These IC methods can be used for product quality control and to determine composition changes in scale inhibitors because of process effects such as thermal degradation or selective adsorption/desorption.

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