Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) is a biocide used in various industrial applications. In the oil and gas sector, THPS is often used to control the growth of bacteria, algae, and fungi in water-based systems such as drilling fluids, completion fluids, and water injection systems. Microbial growth in these systems can lead to various operational issues, including corrosion, fouling, and degradation of fluids. Proper THPS analysis is necessary for optimal dosing and process control.
THPS is effective in controlling microbial activity by disrupting the cellular structures of microorganisms. It is particularly useful in situations where other biocides may be less effective or where there are concerns about environmental impact. Alternative biocides like MEA-triazine or MBO release formaldehyde at neutral pH. Quaternary ammonium compounds are persistent in the environment. THPS is less environmentally persistent while being more stable towards degradation that releases formaldehyde.
The THPS molecule contains two THP+ ions bound with one sulfate. In the presence of a strong base like sodium hydroxide, THP+ will degrade, releasing formaldehyde and tris(hydroxymethyl)phosphine:
Starting with 400 grams of THPS, complete degradation will produce slightly less than 60 grams of formaldehyde. Formaldehyde is easy to measure using colorimetry—or at least it is in clean water that contains no other aldehydes or ketones. In a real-world sample, especially one from an oil & gas application, there will be interfering species. Although the colorimetric method has a strong preference for formaldehyde, high levels of acetaldehyde, for example, can give a false positive.
More importantly, if the sample is colored or dirty, measuring the color change becomes difficult. Filtration or precipitation can eliminate dirty, but a dissolved material that colors the sample will prevent colorimetry from working.
OndaVia’s Quantitative Raman Spectroscopy based on the OPAL-105 platform is an alternative approach that relies upon the colorimetric method with an alternative read-out technique. This method is not affected by turbidity or by sample color. An internal standard is provided for every sample, no blanks or references need to be measured and records. And it offers superior accuracy and detection limits than colorimetric methods. Our ppb-level formaldehyde kit has a 2.5-ppb method detection limit—15-ppb THPS. Our ppm-level kit can read up to 140-ppm THPS without dilution.
