Here we describe the way the process works most:
1. Sampling and preparation
First, a water sample is taken from the well or drinking water.The sample is often filtered to remove solid particles and sometimes concentrated to bring the detectable substances to higher concentrations.
In some cases, a pre-concentration or extraction step may be needed to isolate the compounds of interest. This can be done, for example, using liquid-liquid extraction or solid-phase extraction (SPE).
2. Liquid chromatography (LC)
The prepared water sample is introduced into the LC system.Liquid chromatography separates the components in the water sample according to their chemical properties, such as polarity and solubility. This is done by moving the sample through a column filled with a stationary phase (often a fine-grained silica or other material).
As the sample moves through the column, the different substances will separate at different rates depending on their interaction with the stationary phase and the mobile phase (the liquid flowing through the column).
The separation ensures that the components leave the column at different times, providing a clear separation of the substances in the sample.
3. Mass spectrometry (MS)
After the substances are separated, they enter the mass spectrometer.Here, the molecules are ionised, usually by a technique such as electrospray ionisation (ESI) or chemical ionisation (CI), converting them into charged particles (ions).
The ions are then measured according to their mass-to-charge ratio (m/z) in the mass spectrometer.
The mass analysis provides information on the molecular composition of the substances and can help identify unknown compounds in the sample.
The mass spectrometer generates a spectrum in which the peaks represent the different ions, and the intensity of the peaks provides information about the amount of each substance present.
4. Data analysis
The data coming from the mass spectrometer is analysed by software to identify which substances are present in the water sample, based on their specific mass and charge properties.Comparisons are often made with known reference data or spectrums to confirm the presence of specific pollutants.
5. Results and reporting
The results are analysed and reported. The concentrations of various substances found in drinking water can be determined, and the results can be compared with legal or health standards for drinking water quality.
Applications of LC/MS in drinking water analysis:
- Pesticides and herbicides: Analysis of residues of agricultural chemicals that may enter drinking water through discharges or runoff.
- Pharmaceuticals and hormones: Since many pharmaceuticals and hormones degrade poorly, they can be found in trace amounts in water.
- Industrial chemicals: This may include solvents, heavy metals, or other substances that may enter the environment through industrial activities.
- Micropollutants: These are often new or difficult to detect substances that may be in small amounts in water.
Essentially, the LC/MS helps find substances, which are otherwise difficult to detect, in low concentrations. It is therefore a very valuable technique in ensuring the safety of drinking water.
