In order to not only detect known substances, but to achieve comprehensive monitoring, non-target analysis is available for water monitoring. This highly specialised technique allows water samples to be analysed for unknown substances. Consequently, the water supply company can examine its water down to the last detail and react quickly and specifically to possible anomalies.
The measurement of organic, mostly anthropogenic trace substances in raw and drinking water has long been of high relevance. By detecting potentially harmful substances, it is possible to determine whether critical concentrations in raw and drinking water are exceeded and, if so, whether there is a need for action on the part of the water supplier. When known substances are measured in water resources, this is usually done by means of target analysis. A prerequisite for measurement by target analysis is the availability of reference standards with which the substances in the water samples can also be quantified. Only previously specified substances can be measured with this type of analysis.
Although more substances are constantly becoming known, there is still a high proportion of unknown substances in water samples that can also have negative effects on water quality. Non-Target-Screening (NTS) was developed to include these unknown substances in the monitoring of raw and drinking water. Through NTS, unknown substances can be searched for and also identified. In addition, comparisons between different water samples can be made, accounting for both known and unknown substances. NTS usually consists of qualitative evaluations, although work is also being done on (semi)quantitative approaches.
The origins of NTS date back to the 1970s, when the potential of identifying unknown substances was recognized. Especially in recent years, NTS has attracted increased attention in water resources research and applications through advancements in measurement technology and data interpretation. The measurement is conducted by coupling liquid chromatography (HPLC) to a high-resolution mass spectrometer (TOF or Orbitrap technology).
NTS is already being used in water monitoring to identify substances and compare water samples from different sites, process steps or points in time. The advantage of this method is that a large number of substances can be detected with a single measurement, without having to use a separate method for each substance. NTS is not intended to replace classical target analysis, but should be regarded as a complementary method. Additional information is obtained that provides new insights for the quality assessment of water samples. Furthermore, NTS can also provide direction to target analyses by prioritizing specific signals. Non-target measurements already provide high-quality results, as shown by agreement with previous target analyses regarding the pollution of water bodies.
Further developments in the coming years aim to establish NTS as a routine method in water monitoring. This is already supported by several research projects. A key issue is the comparability of results between users. For this purpose, the exchange of non-target data as well as the development of common quality standards is of high relevance. Furthermore, interlaboratory comparability can be increased by method alignment in measurement and data evaluation. As databases play an important role in the identification of substances, the development of open access databases is essential for the generation of reliable non-target data.
Given these current advancements, it is expected that NTS will increasingly prove to be a useful tool for monitoring raw and drinking water in coming years. The method opens up new possibilities to assess water quality and detect changes. Through the cooperation of non-target users, NTS can also be established in interregional water monitoring.
The laboratory at TZW has many years of experience with NTS and has contributed to numerous research projects in this area. Water supply companies are welcome to contact TZW’s experts with their questions.
The topic was presented at the TZW Colloquium 2022 and can be read in the conference proceedings (in German). To order >