Through the filtration process, contaminants dissolved in the water are collected, and subsequently, gas chromatography (GC) and liquid chromatography (LC) analyses are performed. These are two physical separation methods that will reveal the contaminants present in urban rainwater and their abundance.

Here’s a more detailed description of the process:

1. Collection of Rainwater Samples: Rainwater samples are collected in the Basque Country and Girona. These samples are obtained directly from the rain and stored in clean and sterile containers to prevent any contamination during the collection process.
2. Filtration: The rainwater samples are filtered to separate the contaminants dissolved in the water.
3. Gas Chromatography (GC) Analysis: In this step, the filtered samples are subjected to gas chromatography analysis. Gas chromatography is a technique that separates different components of a mixture based on their chemical properties and affinity for a chromatographic column and carrier gas. This allows for the identification and quantification of volatile compounds present in the sample.
4. Liquid Chromatography (LC) Analysis: The samples are also subjected to liquid chromatography analysis, which is another separation technique used for compounds that are less volatile or soluble in water. Liquid chromatography is based on the separation of components in a liquid phase that flows through a chromatographic column. This enables the identification and quantification of a wide range of compounds dissolved in the sample.
5. Identification of Contaminants: By comparing the retention times and spectra obtained from GC and LC analyses with known patterns of different contaminants, it is possible to identify the types of compounds present in the rainwater samples.
6. Quantification of Abundance: The results from GC and LC analyses also provide information about the concentration or abundance of each contaminant present in the rainwater samples.
7. Data Interpretation: Once contaminants have been identified and quantified, researchers can analyze the results to assess the quality of rainwater in the studied regions. This can help understand the presence and levels of pollution, identify potential sources of contaminants, and evaluate potential impacts on the environment and public health.

Overall, this process of sample collection, filtration, and gas and liquid chromatography analysis provides a detailed insight into the contaminants present in rainwater in the Basque Country and Girona, as well as their relative abundance.