Phosphonate Speciation - Challenges and Solutions

Reliable and accurate analysis of inhibitors is vital for decisions on efficiency and cost-effectiveness of scale inhibitor squeeze treatments. Recent developments have resolved issues for residual sulphonated polymer chemistries which were previously difficult to isolate. Attention now is directed to challenges associated with phosphonate based inhibitors, particularly when assay is required from a multi-component produced water sample containing other P based inhibitor species which currently poses a significant challenge. This paper describes the advantages and limitations of techniques used for phosphorus assay including inductively coupled plasma spectroscopy, ion chromatography and wet chemical methods (e.g. Phospho-molybdenum blue, PMB) approaches. Field examples are discussed to emphasize the analytical challenge with cases whereby speciation is readily achieved and others where this is not the case. To overcome the limitations of these methods, novel approaches for analysis of P – containing inhibitors (in the presence of other –containing additives) include time resolved fluorescence spectroscopy (TRF) and mass spectrometry (MS) detection (which also require development) are considered with potential benefits and limitations / interferences highlighted. These are discussed with highlights of TRF development presented. This technique shows significant scope and potential with promising results showing speciation and discrimination of both polymeric and phosphonate based scale inhibitors as well as a phosphate ester based corrosion inhibitor. This paper highlights the concept that for residual scale inhibitor assay, one analytical approach does not fit all environments and applications. However the availability of a range of techniques, some of which are still in development, allows for effective monitoring in complex, multi-component environments. The paper highlights development opportunities for some of the newer approaches such as TRF and MS as well as discussing their limitations in complex produced fluids.