# Recent Applications of Deep Eutectic Solvents in Environmental Analysis
## Recent Applications of DESs in Environmental Analysis
### Analysis of Inorganic Compounds in Environmental Samples
 } & \multirow{2}{*}{ \begin{tabular}{c} **Extraction** \\ **Procedure** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **Analytical** \\ **Technique** \\ \end{tabular}  } & \multirow{2}{*}{**Recovery**} & \multirow{2}{*}{**LODs**} & \multirow{2}{*}{**Comments**} & \multirow{2}{*}{**Reference**} \\  & & & & & & & - Different HBDs were & \\  & & & & & & & tested to form Binary & \\  & & & & & & DESs and TDESs. & & - A maximum mass & \\  & & & & & & & - & solubility of 0.13 g/g at \\ (-) & & & & & & & 40\({}^{+}\) C was achieved. & & - A selectivity study of \\  & & & & & & & NH\({}_{3}\) to CO\({}_{2}\) was carried & \\  & & & & & & & out. & \\ \hline \hline \multirow{9}{*}{ \begin{tabular}{c} **NH\({}_{3}\)** gas \\ (-) \\ \end{tabular}  } & \multirow{9}{*}{NH\({}_{3}\)} & \multirow{9}{*}{ChC:Lroseronicglycerol (1:5.5; 10 g)} & \multirow{9}{*}{CLE} & \multirow{9}{*}{Gracurimetry} & \multirow{9}{*}{-} & \multirow{9}{*}{-} & \multirow{9}{*}{-} & \multirow{9  
With this aim, both NaDESs [29; 30; 31; 32; 37; 40] or non-NaDESs [27; 28; 32; 33; 34; 36; 38; 39; 41] have been used for the analysis of inorganic species in environmental samples. Regarding their aqueous compatibility, most cases imply the use of hydrophilic DESs [28; 32; 33; 34; 35; 36; 38; 39; 40; 41] even though some examples of quasi-HDESs [33] and HDESs [27] can be found in the literature. As it is shown in Table 2, ChCl constitutes the most used HBA [28; 29; 31; 32; 34; 35; 36; 37; 38; 39; 40; 41], although other quaternary salts such as trihexyl(tetradacyl)phosphonium chloride (THT-DPC) [27] or TBAC [33], as well as N,N\({}^{\prime}\)-dimethyl urea (DMU) [32], or betaine [30] have also been employed. With respect to the HBDs, different alcohols [30; 32; 34; 35; 36; 38; 39; 41] and organic acids [27; 28; 31; 32; 37], as well as urea [29; 40], sugars [32], and fatty acids [33] have been used. DESs were mainly used as extraction solvents and without any doubt, LLME approaches [27; 30; 31; 33; 34; 35; 38; 39; 41] stand out, but other extraction techniques were applied based on solid-liquid extraction (SLE) [32; 37], m-u-dSPE [29; 40], and gas-liquid extraction (GLE) [36]. In the case of LLME techniques, the emulsification LLME (ELLME) based on the use of an aprotic solvent as emulsifier to achieve phase separation was the mainly used extraction method [30; 31; 34; 35; 38; 39; 41], although some works in which a disperser has been applied can be also found in the literature [33]. In these cases, one of the main challenges is the collection of the drop after the extraction and as previously mentioned,  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline Sample & \multirow{2}{*}{Analytes} & DES & \multirow{2}{*}{Extraction Procedure} & \multirow{2}{*}{Analytical Technique} & \multirow{2}{*}{Recovery \%} & \multirow{2}{*}{LODs} & \multirow{2}{*}{Comments} & \multirow{2}{*}{Reference} \\ (Amount) & & & & & & & & & \\ \hline \multicolumn{10}{c}{- Soil samples were received (0.2 g)} \\ River tap, & \multirow{2}{*}{Cd(II)} & \multirow{2}{*}{ChClurea (1:2.5;200 \(\mu\)L)} & \multirow{2}{*}{m-u-dSPE} & \multirow{2}{*}{FAAS} & \multirow{2}{*}{95–105} & \multirow{2}{*}{0.1–0.4 g/L} & \multirow{2}{*}{also evaluated in combination with DES.} \\ well, and sea & & & & & & & -1 M HNO was used as \\ water (60 mL) & & & & & & & & \\  & & & & & & & & (600 \(\mu\)L). \\  & & & & & & & & - A Selectivity study was \\  & & & & & & & & & carried out using potential interfering ions. \\  & &  
among the proposed solutions was the solidification of the organic droplets to promote the obtention of the analytes-enriched extract. However, this alternative cannot be useful when a DES with a very low freezing point is used. Thus, the solidification of the aqueous phase could be a tedious task, but at the same time, it could be a great solution to this issue [27].