Single drop microextraction (SDME) nowadays earns an increasing attention by scientists due to its simplicity, low cost and the need for only common laboratory equipment. This microextraction technique combines sample cleanup and pre-concentration of analytes in one step. Furthermore, a significant reduction in the amount of organic solvents needed comparing to standard LLE techniques places SDME into the position of environmental friendly extraction techniques. SDME is a straightforward technique in which a micro-drop of solvent is suspended from the tip of a conventional micro-syringe and then it is in a direct contact with a sample solution in which it is immiscible or it could be suspended in the headspace above the sample. The paper overviews developments of the state-of-the-art SDME techniques for the extraction of harmful organic compound and pollutants from environmental, food and biological matrices. Key extraction parameters essential for SDME performance were described and discussed.

Single drop microextraction technique uses microamounts of organic solvents. Simplicity, low cost, low environmental impact, compatibility with chromatographic systems as well as its applicability to different matrices are main advantages of single drop microextraction. This technique has become frequently used for the extraction of a broad scope of compounds for numerous analytical applications. This review provides an overview of the existing single drop microextraction modes of realisation and the main scope is devoted to the optimization of parameters influencing the efficiency. The state of the art is discussed on the basis of examples selected from representative application areas. Extraction parameters for toxic organic compounds extraction and microdrop stability were evaluated.

With the increasing consumption of coffee beverages, an increased amount of food waste—spent coffee grounds (SCG)—is generated and disposed into landfills or combusted in incinerators. SCG are characterized as a highly polluting substance with partial toxicity due to the presence of caffeine, tannins, and polyphenols. It also contains 15% of oil on average, and its potential for biodiesel production is thus considerable. The aim of the presented work is to evaluate the possibility and technical potential of biodiesel production from the SCG oil (SCGO) by esterification and transesterification reaction. According to the characterization of the studied SCGO, this stream must be adjusted and purified to be utilized in the existing biodiesel production plant. Fatty acids (FA) represent 85.85% of the SCGO, with two dominant FAs—linoleic and palmitic acids. The necessity of removal and disposal of unsaponifiable matter, which accounts for 15% of the SCGO content, must be highlighted when producing biodiesel from the SCG. The objective of this research was the comparison of different biodiesel production processes, where a two-step transesterification process has been identified as the most successful method for biodiesel production from the SCGO with the highest ester content of 89.62% and the lowest content of unsaponifiable and unidentified matter in the final product. The novelty of the analyses is a characterization of the d unsaponifiable matter present in the SCGO, and the article highlights the importance of progression to be considered when evaluating the technical potential of the SCG biodiesel production integrated into a biorefinery. Nevertheless, the SCG biodiesel can contribute to fulfilling the mandatory share of advanced biofuel in the fuel energy mix given by national legislation and contribution to the circular economy approach of biorefineries.

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.