Non-target screening

Suspect screening and non-target screening explained

A broad, generic screening method detects a multitude of chemical substances simultaneously and at low concentrations. This results in a long list of thousands of unknown substances (also called ‘features’) for each sample. Within these features, we look for the harmful and/or relevant substances. Using suspect screening, also known as library screening, the results are compared with a ‘suspect’ list of substances that are thought to be present in the sample, such as substances of very high concern and their metabolites, PFAS or substances associated with certain industrial processes.

Non-target screening looks at the remaining, unidentified substances and makes it possible to search for trends and differences between samples. Suspect and non-target screening can also be used to examine historical data, to retrospectively detect substances in the raw data of samples measured in the past.

Suspect and non-target screening can identify a wider spectrum of chemical substances.

By contrast with target screening, the identity of a substance found with suspect and non-target screening cannot always be confirmed with 100% certainty. The level of uncertainty in identification is explained using five confidence levels (Schymanski et al. 2014). Fullidentification can only be achieved when a reference standard for the substance in question is measured using the same system.

By contrast with target screening, suspect and non-target screening cannot always establish the identity of the substance found with the same level of certainty.

The level of uncertainty of the identification affects possible follow-up steps such as the determination of concentrations, predictions of hazards and risks for humans and the environment. Semi-quantification is often used to nevertheless provide an estimate of the concentration of the (un)known substance.

The results of suspect and non-target screening can be used for a range of follow-up steps such as risk assessment and monitoring trends and seasonal effects.

Continuous development

We are constantly expanding and optimising our suspect and non-target screening methods to better identify and eventually quantify more substances. There is a major focus on measuring highly polar substances, which are mobile and therefore highly relevant for drinking water because they can easily enter groundwater and are difficult to remove in water treatment plants. We have developed a method that nevertheless makes it possible to analyse these difficult-to-detect substances. The transformation products (breakdown products) formed in water treatment plants also pose a challenge to water quality. We developed a method to monitor them better with the help of suspect and non-target screening. We are also engaged in fundamental research into the improved prioritisation of unknown substances that may be harmful for humans and the environment.