Abstract
Abstract Single drop microextraction has become a widespread liquid/liquid microextraction technique owing to its simplicity, high preconcentration factor and low consumption of organic solvents in the extraction due to direct introduction of the very low volume of extract into the analytical system. Crucial features ensuring excellent repeatability of single drop microextraction include: solvent volume, solvent type, sample agitation, salts addition, and pH. The influence of sample quality on the microdrop volume and agitation type was studied. Effect of the sample matrix, such as water, acid content samples (orange juice), sample containing alcohol (plum brandy) and protein content sample (milk), on the microdrop hold-up was also investigated. For water analysis, several organic solvents such as chloroform, dichloromethane, tetrachloromethane, tetrachloroethane and chlorobenzene were tested; last three mentioned were suitable for SDME experiments. For milk samples analysis, chlorobenzene microdrop was found to be optimal; advantage of salt addition has been reported. For orange samples, 1:10 dilution was suggested with stable microdrop volumes (toluene) of up to 6 µL for lower stirring rates (100 rpm and 250 rpm). For alcohol-content samples, the change of alcohol percentage of real-life samples had to be considered. A strong influence of the matrix quality on the microdrop stability has been proven.
Highlights
Actual trends in analytes extraction from various food or environmental samples follow green che mistry philosophy taking into account simplification and miniaturisation, especially minimisation of the volume of necessary organic solvents which are potentially harmful and unwanted in large scale in analytical procedures (Hrouzková, 2017)
The ease of dislodgment of the microdrop hanging from the tip of the microsyringe needle during the extraction process limits the use of extended extraction times, high stirring rates, sample temperature and the type of sample matrix (Jain and Verma, 2011)
Samples Orange juice (100 %), plum distillate (40 % alc.), and milk (0.5 % of fat) were purchased from local shops. These samples were diluted with deionised water and used for the extraction as follows: Orange juice was diluted in the ratio 1:2 (v/v) and 1:10 (v/v), alcohol samples were each diluted to 20 % alc., and milk was diluted in the ratio 1:10 (v/v)
Summary
Actual trends in analytes extraction from various food or environmental samples follow green che mistry philosophy taking into account simplification and miniaturisation, especially minimisation of the volume of necessary organic solvents which are potentially harmful and unwanted in large scale in analytical procedures (Hrouzková, 2017). For the liquid-liquid extraction, a set of techniques called liquid-phase microextraction (LPME) has underwent a dramatic increase in a variety of approaches (Andraščíková et al, 2015) using only microliters of solvent to preconcentrate analytes from various samples rather than hundreds of millilitres needed in traditional LLE (Sarafraz-Yazdi and Amiri, 2010) One of these techniques, single-drop microextraction (SDME) (Liu and Dasgupta, 1995) has drawn much interest. Development of an analytical method using SDME requires optimisation of a high number of variables and parameters affecting the extraction step It has been shown in our previously published review (Zichová et al, 2018b) that parameters such as the type of investigated analytes, quality of the extraction solvent, type of microsyringe, sample volume, physical properties such as temperature, ion strength and pH of the sample affect the efficiency of the extraction procedure. A few comprehensive information on the influence of the liquid sample matrix on the stability
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