## 3 Analytical Instrumentation  
### Chromatography in Water Analysis  
Monitoring environmental contaminants have grown rapidly and significantly in recent years, becoming a crucial analytical science area, developing new and innovative analytical techniques to identify and quantify pollutants in trace concentrations in the environment. Despite which sample preparation methods used for water sample enrichment, additional steps, including chromatography for separation and further quantification, can increase the data's quality. Therefore, the interest in developing high performance, robust, and sensitive chromatographic methods has also increased. Consequently, new stationary phases, columns, and instruments have appeared, intending to simultaneously shorten the analysis time and obtain greater resolutions and sensitivities [78]. Currently, chromatography is considered to be the most used and versatile technique due to several factors: (i) the availability of very sensitive detection methods for all categories of chromatographic techniques; (ii) the relative speed of chromatographic separations; (iii) ease of use when compared to other analytical methods; and, (iv) the possibility of developing precise and trueness analytical methods. The quantitative chromatographic analysis is used in all analytical chemistry areas, being essential in environmental sciences, namely in the monitoring of organic compounds in water matrices. Besides, the various organic parameters that are defined in the national and European legislation on the quality of water [28; 29; 164; 165], pesticides, polycyclic aromatic hydrocarbons (PAHs), trihalomethanes, and alkyl halides, among others, are determined while using chromatographic techniques, as gas chromatography and liquid chromatography. These two techniques are also the techniques of choice in PhACs analysis. The development of analytical methodologies for determining pharmaceuticals in environmental matrices, mainly in water, has boomed in the past years. In this context, the analytical challenges, primarily in quantitative analysis, had focused not only on the development of novel sample preparation methods (or new materials), but also on fast chromatographic methods, most of them being coupled to mass spectrometry (MS) [96; 166; 167]. Although gas chromatography has a high resolving power and it has been applied in the determination of PhACs, they are mostly polar and not very volatile or thermally unstable, which makes its direct determination by GC impossible, which implies the use of a derivatization step. Therefore, liquid chromatography (LC) has become the selected tech nique, as it allows the determination of PhACs from different therapeutic classes and with different physical-chemical properties after sample preparation techniques [168; 97; 169]. The main advantages of LC include the separation of a wide variety of compounds present in different samples, regardless of volatility, thermal stability, and polarity, in a few minutes, with high resolution, efficiency, and repeatability. Literature shows the determination of PhACs in water samples by LC coupled with different detection techniques, such as ultraviolet and diode detectors [149; 150] or fluorescence [20; 60; 110]. However, liquid chromatography coupled with mass spectrometry (MS) is the most used. The coupling of liquid chromatography with the mass spectrometer combines the advantages of chromatography (high selectivity and separation efficiency) with mass spectrometry (structural information, molar mass, and increased selectivity and detectability) [49]. HPLC has undergone some considerable improvements, especially in terms of innovative stationary phases and instrumentation. Short narrow-bore columns that are packed with fully porous sub-2 \(\upmu\)m particles together with instruments exhibiting reduced extra-column volumes and able to withstand pressures up to 1000-1300 bar. This type of chromatography is known as ultra-high performance liquid chromatography (UHPLC) or ultra-performance liquid chromatography (UPLC).