**5. List of abbreviations**

204 Chromatography – The Most Versatile Method of Chemical Analysis

their metabolites in environmental samples [47, 55].

environments.

the same run.

**4. Conclusion** 

allows the molecule to "wrap" itself around that cation [64]. Thus, sodium acetate [60, 74], ammonium acetate [89, 142] or different acids [53] are commonly added to the samples or to the mobile phase to increase the MS response of NPEOs and AEOs and to stabilize the generation of [M+Na]+, [M+NH4]+ or [M+H]+ ions, among others. Additionally, this ability to form different adducts can be used to obtain multiple confirmation points in full-scan mode [40]. Another advantage of MS compared to other detectors is that several types of surfactants can be analyzed within a single run (e.g., NPEOs and AEOs can be separated, using an adequate gradient, and later analyzed under PI [53, 64]). Most recent methodologies allow simultaneous determination of anionic and non-ionic surfactants and

Today, mass spectrometry is often combined with ultra-performance liquid chromatography (UPLC), which uses sub-2-µm column particles that provide enhanced separation, faster analysis, and improved sensitivity over HPLC, boosting laboratory efficiency by saving time and decreasing solvent consumption. Most researchers have started to benefit from this combination, although there are still a few examples on its use for analysis of surfactants. So far, UPLC-Q-ToF-MS has been used for structural elucidation of SPC isomers [139] and for environmental screening of several anionic and non-ionic surfactants in wastewater [138]. UPLC-MS-MS [44] has allowed achieving fast analysis (less than 10 min per sample) of NPEO metabolites and AEOs at trace levels in aquatic

The assessment of the behavior and final fate of synthetic surfactants in the environment is a crucial matter due to the huge volumes of these chemicals that are discharged into aquatic and terrestrial ecosystems. A significant number of analytical protocols have been developed over the last decades aimed to the individual or simultaneous extraction, isolation and determination of different types of surfactants in environmental samples. Nowadays, the most widely used sample preparation protocols are based on SPE, directly derived from column chromatography. However, the trend is to research on new techniques, such as SPME or SBSE, aimed to reduce, or even eliminate, solvent consumption, as well as saving money by using reusable fibers and bars rather than disposable cartridges. Regarding the separation, identification and quantification of surfactants, HPLC-MS and, to a lesser extent due to the non volatility of most analytes, GC-MS, are the main tools currently employed as they allow for determination of every single homologue, ethoxymer and/or isomer from surfactant mixtures in different environmental matrices (solids, water and biota). Most recently, different classes of time-of-flight and triple quadrupole mass spectrometers have started to be combined with UPLC, which provides enhanced separation, faster analysis, higher confidence, and lower detection limits than more conventional HPLC-MS or HPLC-MS-MS approaches, as well as improves identification of unknown surfactant metabolites and other non target compounds within AA, Acetic acid; ASE, Accelerated solvent extraction; ACN, Acetonitrile; AEOs, Alcohol polyethoxylates; AES, Alkyl ethoxysulfates; AS, Alkyl sulfates; ATACs, Alkyltrimethylammonium chlorides; AP, Alkylphenol; APEOs, Alkylphenol polyethoxylates; APEC, Alkylphenol polyethoxycarboxylate; AMAC, Ammonium acetate; APCI, Atmospheric pressure ionization; BACs, Benzalkonium chlorides; BSTFA, N,Obis(trimethylsilyl)trifluoro acetamide; CWAX/TR, Carbowax/template resin; CI, Chemical ionization; DTDMAC, Dehydrogenated tallow dimethyl ammonium chloride; DADMAC, Dialkyldimethylammonium chlorides; DCM, Dichloromethane; DLLME, Dispersive liquidliquid microextraction; EI, Electron impact ionization; ESI, Electrospray ionization; EO, Ethylene oxide; CESIO, European Committee of Organic Surfactants and their Intermediates; FID, Flame-ionization detectors; FIA, Flow-injection analysis; FL, Fluorescence detectors; FA, Formic acid; GC, Gas chromatography; GBC, Graphitized black carbon; HPLC, High-performance liquid chromatography; HLB, Hydrophilic-lipophilic balance; LOD, Limit of detection; LOQ, Limit of quantification; LAS, Linear alkylbenzene sulfonates; LC, Liquid chromatography; LLE, Liquid-liquid extraction; MS, Mass spectrometry; MSPD, Matrix solid-phase dispersion; MeOH, Methanol; MLD, Method limit detection; MAE, Microwave-assisted extraction; NC, Naphthyl chloride; NI, Negative ionization; NP, Nonylphenol; NPEOs, Nonylphenol polyethoxylates; NPECs, Nonylphenol polyethoxycarboxylates; OP, Octylphenol; OPEOs, Octylphenol polyethoxylates; PA, Polyacrylate; PEGs, Polyethylenglycols; SDB, Polystyrene-divinylbezene; PDMS/DVB, Polydimethylsiloxane/divinylbenzene; PI, Positive ionization; PT, Potentiometric titrametration; PFE, Pressurized fluid extraction; PLE, Pressurized liquid extraction; Q-ToF, Quadrupole time-of-flight; QACs, Quaternary ammonium-based compounds; SIM, Selected ion monitoring; SDS, Sodium dodecyl sulphate; SLE, Solid-liquid extraction; SPE, Solid phase extraction; SPME, Solid phase microextraction; SBSE, Stir-bar sorptive extraction; SAX, Strong anionic-exchange; SCX, Strong cationic-exchange; SPCs, Sulfophenyl carboxylic acids; SFE, Supercritical fluid extraction; MS-MS, Tandem mass spectrometry; ToF, Time-offlight; UPLC, Ultra performance liquid chromatography; UV, Ultraviolet detectors; WWTPs, Wastewater treatment plants.
