Analyzing for quat salts has been an age-old challenge. Some methods work for specific situations such as colorimetry with methyl orange for tetrabutylammonium in water. Decomposition of tetrabutylammonium in the injector port of a gas chromatograph followed by detection of tributylamine has been tried but found to suffer from low reproducibility.
This month we want to highlight a newly patented method that not only analyzes a variety of quat ammonium cations, it does so using a crude sample with no pre-purification.
The invention described in Cooks; R., Jjunju; F., Li; A., Roqan; I. (Purdue Research Foundation) US Patent 11,300,555, 12-Apr-2022 provides a method for analyzing a crude oil sample by mass spectrometry in an unmodified form from which the sample was obtained. The invention provides for rapid and efficient monitoring of quaternary ammonium corrosion inhibitors in the crude oil in transmission pipelines using a bench mass spectrometer that can be deployed in the field under ambient conditions.
According to the invention a drop of crude oil containing quaternary ammonium salts is placed on filter paper and then a “discontinuous atmospheric pressure interface” (DAPI) is used with the bench-top or miniature mass spectrometer to perform the analysis.
Quaternary ammonium cations present in crude oil samples that were successfully analyzed by this method include tetrabutylammonium, tetraoctylammonium, tetrahexylammonium, tetradodecylammonium, hexadecyltrimethylammonium, benzylhexadecyldimethylammonium and alkyldimethylbenzyl ammonium.
Historically, we have not seen MS used for the analysis of quats. We assumed that this might be due to the low volatility of quat salts for applications such as GC-MS. This patent clearly demonstrates a practical system using MS to analyze quat salts in a crude non-treated oil sample.
When your company needs help in choosing a quaternary ammonium salt to achieve low-cost high-performance green chemistry using PTC, now contact Marc Halpern of PTC Organics to explore collaboration through consulting.
