Menthol-Based Deep Eutectic Solvent Dispersive Liquid–Liquid Microextraction: A Simple and Quick Approach for the Analysis of Phthalic Acid Esters from Water and Beverage Samples

Abstract

In this work, a natural deep eutectic solvent (NADES) composed of l-menthol:acetic acid 1:1 (molar ratio) was applied for the first time as the extraction solvent for the dispersive liquid–liquid microextraction (DLLME) of a group of 9 phthalic acid esters (i.e., dipropyl phthalate, DPP; butyl benzyl phthalate, BBP; dibutyl phthalate, DBP; diisopentyl phthalate, DIPP; di-n-pentyl phthalate, DNPP; dicyclohexyl phthalate, DCHP; di­(2-ethylhexyl) phthalate, DEHP; diisononyl phthalate, DINP; and diisodecyl phthalate, DIDP) from different water samples (i.e., tap and mineral water) and an apple juice beverage. Dihexyl phthalate (DHP) and di-n-octyl phthalate (DNOP) were used as internal standards. After addition of the DES, agitation, and centrifugation, the NADES droplet was collected, dissolved in the mobile phase, and injected in a high-performance liquid chromatograph coupled to a UV detector. Relative recovery percentages were in the range 71–120% with relative standard deviation values ≤20%, while the limits of quantification of the method were in the range 3.6–22 μg/L for tap water, 3.8–20 μg/L for mineral water, and 4.0–23 μg/L for an apple juice drink. Infrared spectroscopy and differential scanning calorimetry analysis of the DES drop after the DLLME procedure revealed the absence of the DES after the extraction and the existence of an l-menthol-rich phase as a result of an important transfer of acetic acid to the aqueous phase. However, the use of l-menthol alone, which required the previous thermal solubilization of l-menthol, was not able to quantitatively extract some of the target analytes. The extraction carried out after the thermal solubilization of l-menthol and the addition of an acid like HCl suggested that the extraction capacity of the DES is caused by a “transient network” originated by the acidity of the medium, independently of the nature of the acid. The optimized NADES-DLLME procedure was extremely simple, quick, and also environmentally friendly, as a result of the biodegradability and relatively low toxicity of both components of the DES.

Quality assessment of environmental water by a simple and fast non-ionic hydrophobic natural deep eutectic solvent-based extraction procedure combined with liquid chromatography tandem mass spectrometry for the determination of plastic migrants

“…The main aspects of the developed method performance were compared with those in which alternative solvents were employed for the extraction of plastic migrants from water matrices (Table 3 ). In this regard, the LOQ values obtained in the present work are much lower than those obtained in previous works in which the evaluation of PAEs and/or DEHA in water samples was carried out using DESs [ 50 ] or ILs [ 51 – 55 ]. Only the approaches developed by Mogaddam et al [ 56 ] and Mirzajani et al [ 57 ], in which polyethylene-packed injection solutions and mineral water were analysed, respectively, obtained LOQs in the same order.…”

“…The use of adequate surrogates or instrumental internal standards that guarantee the reliability of the obtained data should be considered. In this sense, the use of isotopically deuterated compounds is preferred since the application of other PAEs, which although are not included into the target selected compounds, have been demonstrated to be in the evaluated samples [ 59 – 61 ] as occur in the works of Ortega-Zamora et al [ 50 ] and Mogaddam et al [ 56 ], which could pose serious doubts on the reliability of the obtained results. This practice is especially questionable when, in addition, the selected surrogates are also classified as toxic substances and priority pollutants with prevalence in the environment [ 3 , 5 – 7 ].…”

“…This work constitutes a very simple method that does not entail any modification of the initial conditions of the samples, including pH or temperature, in contrast to others such as that of Ortega-Zamora et al [ 50 ], Mogaddam et al [ 56 ], or Mirzajani et al [ 57 ]. Moreover, the high water stability of the thymol:menthol HNADES employed [ 18 ] in contrast to other DES previously applied for the evaluation of aqueous matrices has been demonstrated [ 50 ].…”

Deep Eutectic Solvents Application in Food Analysis

“…As a consequence, Shishov et al [6] proposed a new term for these unstable HDESs in aqueous phase: "quasi-hydrophobic DES", since it would not be appropriate to consider them as HDESs. In most of the works collected in this review, a study has not been carried out to verify if the extraction is due to a HDES or to one of its components as consequence of the leaching of the other one, as it was verified, for example, in the study carried out by Ortega-Zamora et al [96]. That is why in this section both the HDESs and the quasi-hydrophobic DESs that have been used for the analysis of food samples, have been grouped and are shown in Table 2.…”

“…Currently, studies on the synthesis and application of HDESs for the extraction of a great variety of analytes from food matrices have expanded rapidly, which has led to an increase in the number of articles published in recent years. As can be seen in Table 2, several HDESs have been used for the extraction of both organic (phthalic acid esters [18,96,99], dyes [97,104,110,117], PAHs [17,85], sterols [98], pesticides [100,105,112,122,124,126,127], herbicides [102], insecticides [125], preservatives [101], pigments [86], antibiotics [87,103,108,114], fluorescent whitening agents [106], vitamins [107], mycotoxins [16], bisphenols [115], perfluoroalkyl substances [120] and terpenes [121]) and inorganic compounds (Co, Cd, Ni, As, V and Pb [109,111,113,116,118,119,123]) from aqueous phases (water [96,113,118,124], soft drinks…”