Overview analysis of unknown substances, known in English as “Non-Target Screening” (NTS), is about being able to detect substances that are not already known or suspected to be present in the sample. This capability is particularly important in problem-solving and investigations of, for example, emissions. When ordering an overview analysis from a routine laboratory, this often means that only a predetermined number of compounds are detected, since this makes the analysis and quantification significantly easier to perform. However, if there are other, even very similar substances in the sample that are not included among these, they will not be detected.
In overview analyses of unknown substances, a somewhat different approach is used, looking more for types of substances, for example substances within a certain boiling point, size or polarity range. Quantification also has to be performed differently, since there are no standards/reference substances available to purchase and calibrate against. Instead, something called semi-quantitative determination is often used, which means that one or more reference substances are used to determine response factors, which are then applied to the unknown substances that are detected.
There are mainly two analytical techniques used for overview analyses of unknown substances: gas chromatography with mass spectrometric detection (GC-MS) and liquid chromatography with high-resolution mass spectrometric detection (LC-HRMS). For more information about the techniques, click on the link for the respective abbreviation. Industridoktorn has access to both of these analytical techniques and can analyse samples from, for example, air, water, organic solvents and solid materials, as well as process liquids and mixtures of various kinds. Field sampling can be performed both manually using discrete samplers and by automated robots with sampling and logging of sensor data.
In our laboratory, we can accept products for analysis or set up simulations of different processes or parts of processes where, for example, unknown by-products or contaminants can be analysed.
A third technique, primarily used in the field, is various types of general sensors, such as a flame ionisation detector (FID) or photoionisation detector (PID), which detect hydrocarbons, NPD, which detects nitrogen-containing compounds, or some type of VOC sensor. These provide a relatively predictable signal for the substances detected and can therefore be used to obtain a rough determination of concentration, but they provide no information that can be used to identify which substances were detected. When performing overview analysis of unknown substances, such sensors therefore need to be combined with sampling and analysis in which the substances can be separated and identified, such as the GC-MS or LC-HRMS techniques described above.