Towards a water-wise world Annual report 2014

TPA is detected most often, but at levels far below the maximum standard 

Detecting quaternary ammonium compounds in water

25 June 2014BTO

KWR researches at 21 sites whether quaternary ammonium compounds (quats) are present in the water used to produce drinking water. To this end, within the water sector’s joint research programme (BTO), a new analytical method, which can detect quat concentrations at levels far below permitted standards, has been developed and implemented. During the monitoring, one quat is present most often: tetrapropylammonium (TPA), but always in quantities that pose no threat to drinking water quality. Periodic monitoring with the new method will help prevent the presence of TPA from becoming a problem in the future.

Quats are industrial chemical compounds used in households, industry, farming and medical practice. In 2010, the National Institute for Public Health and the Environment (RIVM) judged that quats in surface water could have an effect on drinking water production, and that it was important to research how often, and in what quantities, these compounds occur in surface water. At that time, the water sector did not have any good analytical methods for the various types of quats. So KWR has developed an analytical method for the water companies, which is able to monitor 27 of the most relevant quats in the water used to produce drinking water.

An analytical method to monitor 27 of the most relevant quats

Chromatography and QTOF mass spectrometer

The new analytical method uses 2 kinds of chromatography to separate the different compounds in the water samples: reversed phase for hydrophobic quats, and HILIC for hydrophilic quats like paraquat and diquat. A high-resolution QTOF mass spectrometer is then used to detect and identify the quats. Researcher Dennis Vughs says that “with the QTOF one can measure the relevant compounds, such as quats, in very low concentrations; also, during the analysis, one can screen for ‘unknown’ compounds. The new method of detecting and identifying quats delivers easily-reproducible results, and detects the compounds in concentrations far below 0.1 microgram/l, which is the maximum permitted under the drinking water standards.”

Monitoring for TPA

The monitoring encountered one quat most often: tetrapropylammonium (TPA). TPA appears in 11 of the 21 sites, as well as in drinking water samples – but always in concentrations far below the permitted level. TPA therefore does not currently constitute a threat to drinking water quality. Periodical monitoring with the new methods can prevent this compound from becoming a problem later on, because timely measures will be able to be taken if quantities begin to increase.

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