## 3 Extraction and Analytical Methods
### Analytical Method  
After the sample pretreatment and the phthalates extraction, they are determined by quali/quantitative analysis using instrumental techniques which, together with the extraction techniques, determine the quality of the detection. The variables that regulate the choice of the appropriate analytical technique depend on the type of analyte and the instrumental sensitivity.  
The most commonly used methods are gas chromatography (GC) and liquid chromatography (LC) coupled to detectors such as mass spectrometer (MS), which allows measuring the mass/charge ratio (m/z) of analytes [34]. Generally, MS detector is selected as the best detector system for these types of analyses; moreover, in the case of water samples, analyses by LC instrument can be performed without extraction or purification systems.  
Gas chromatographic analysis is the most widely used separation technique for PAEs analysis, as phthalates have volatile and thermostable characteristics [52]. Generally, non-polar capillary chromatographic columns (in a thermostatic oven) and helium gas are used.  
Gas chromatography coupled with MS has many advantages, such as a short analysis time, high resolution, and sensitivity [34]. With the MS detector, each PAE can be ionised by electronic impact (EI) and detected by full scan, single ion monitoring (SIM), selected ion storage (SIS), MS tandem (MS/MS), or multiple reaction monitoring (MRM), improving its sensitivity [34; 52].  
High-pressure liquid chromatography is a technique that allows the separation of two or more compounds present in a solvent, exploiting the affinity equilibrium between a mobile phase, in which phthalates are dissolved (mixture of liquid-pressurised solvents usually consisting of acetonitrile and water) and a stationary phase (absorbent material, typically granular silica or polymer) is placed inside the chromatographic column [53; 56].  
Phthalates can be analysed using liquid chromatography coupled to mass spectrometry (LC-MS) with electrospray (ESI), or atmospheric pressure chemical (APCI), and ionisation in positive mode [34; 52].  
Detectors such as diode array detector (DAD) are also used in the literature or UV coupled with LC, which have the advantage of being economic techniques with good performance where dissolved analytes can be recovered; however, these have slightly lower sensitivity than GC methods [57].  
Notably, when comparing GC and LC results in PAEs analyses, the latter showed a lower sensitivity for major phthalates [34; 52], while HPLC, and more recently, ultra HPLC (UHPLC) were more adequate for the analyses of PAEs' degradation products and for PAEs' isomeric mixtures (e.g., DiNP, DiDP) [52].  
In fact, low detection limits in water samples for the following analytical techniques have been reported: LC-MS analysis of ten mono-alkyl phthalate esters (MPEs) of 0.19-3.9 ng/L; GC-MS analysis of five PAEs: 1.62-16.3 ng/L; and LC-UV analysis of three PAEs: 10-20 ng/L [52].  
Among the mass spectrometry instrumentation combined with either the LC or GC system (quadrupole, triple quadrupole, ion trap, and magnetic sector), the triple quadrupole is the most frequently used for strength, sensitivity, and stability [52]. In addition, more recently quadruple hybrid systems associated with TOF and Orbitrap, and the latter in particular has excellent resolution, mass accuracy, sensitivity, and selectivity for phthalates [58; 59].  
Although less used, other chromatographic techniques replacing LC or GC for PAEs analysis are micellar electrokinetic capillary chromatography (MEKC), Fourier transform infrared spectroscopy (FTIR) and colourimetric analysis. Similarly, non-chromatographic methods are also less used than GC and LC and rely on recent molecular imprinting technologies and immunoassay-based techniques. The advantage of these techniques is that they have a lower maintenance cost and fewer blank contamination problems than LC and GC. However, these techniques are still in development [34; 52; 57].