Application Of Dispersive Liquid-liquid Microextraction For Analysis Of Complex Foods

In recent years, more favour has been focused on miniaturized sample preparationtechnique. Under this circumstance, dispersive liquid-liquid microextraction (DLLME) as anew liquid-phase microextraction (LPME) technique has come into being. It has beenincreasingly applied for the extraction of both inorganic and organic analytes from differentmatrices due to its simplicity, low cost and solvent consumption, and high enrichmentefficiency. However, due to the poor selection of DLLME, the interferences from matrixco-extractives often occur, which limits further application of DLLME for analysis of traceanalytes in complex foods. This work describes the development of three novel samplepreparation methods based on DLLME for analysis of complex foods. The research results aresummarized as follows.1. A DLLME method coupled with high performance liquid chromatography wasdeveloped for analysis of α-tocopherol in pigmented wheat samples. The DLLME parametersincluding the type and volume of extractants, the volume of disperser and the addition of saltwere examined. The method was successfully applied to42samples of14types of pigmentedwheat, and the results showed the content of α-tocopherol exhibited a significantly negativecorrelation with the pigment content measured by a spectrophotometer. This method wasbased on reducing the four steps in the national standardized method (extraction, washing,drying and concentrating via rotary evaporation) to two main steps, extraction andcentrifugation, which shortened the extraction time from4h to40min. Additionally, thequantity of required organic solvent was decreased from200mL to80μL for one extraction.The DLLME was accurate, high efficient, low organic solvent-consuming and low-cost. Thedeveloped approach shows great potential for analysis of micronutrients in food.2. Two novel sample extraction methods for analysis of bisphenol A (BPA) in edible oilswere developed by using liquid-liquid extraction followed by dispersive liquid-liquidmicroextraction (LLE-DLLME) and reversed-phase dispersive liquid-liquid microextraction(RP-DLLME). In LLE-DLLME mode, with1-octanol as extractant, the DLLME procedurewas accomplished by use of a disposable polyethylene pipet with narrow and long neck,which enabled the easy collection of1-octanol phase after the microextraction. In RP-DLLME mode, the DLLME extractant was100μL of0.2M sodium hydroxide solution(80%methanol, v/v) rather than the high toxic halogenated hydrocarbons that have been usedmostly in classic DLLME. The aqueous extractant successfully extracted BPA from oil matrix,being compatible with RP-HPLC mobile phase. RP-DLLME showed a superior characteristicover LLE-DLLME and other previously reported procedures because of its easy operation,short extraction time, high sensitivity, low organic solvent consumption and waste generation.This procedure could be used for analysis of phenolic compounds in oil or fatty samples.3. A new method combined dispersive solid-phase extraction (DSPE) and ionicliquid-based dispersive liquid-liquid microextraction (IL-DLLME) was developed for analysisof phthalic acid esters in edible oils. Sample treatment involved initial liquid-liquidpartitioning with acetonitrile, then DSPE cleanup with primary secondary amine as sorbent.Preconcentration of the analytes was performed by IL-DLLME using the cleaned-up extractas disperser solvent and1-hexyl-3-methylimidazolium hexafluorophosphate as extractionsolvent. Under the optimal conditions, the procedure could achieve good clean-up andpreconcentration effec, and had good linearity, precision and accuracy. This was successfullyused for analysis of the analytes in28edible oils. The combination of DSPE and IL-DLLMEwould provide a new way for analysis of trace analytes in complex food.