Successive liquid-phase microextraction of acidic and basic analytes.

Practical biological and environmental samples always contain both acidic and basic substances, and the samples are always precious. Thus, separation of analytes with different nature from the same sample was of great significance. Successive liquid phase microextraction (sLPME) of acidic and basic analytes under optimal extraction conditions was therefore proposed for the first time. The concept of sLPME was proved by using three acidic analytes (naproxen, flurbiprofen and diclofenac) and three basic analytes (haloperidol, fluoxetine and sertraline) as model analytes, and using polypropylene glycol with an average molecular weight of 4000 (PPG4000) as SLM. The recoveries of all target analytes by sLPME were similar to that by individual LPME due to good affinity of PPG4000 to both acidic and basic analytes. Under optimal extraction conditions, the recoveries for all analytes by sLPME from urine samples were in the range of 62%-95%. Moreover, combined with LC-MS/MS, such sLPME approach was also evaluated with urine samples. The matrix effect of sLPME-LC-MS/MS at different levels for all analytes ranged from -14.1%-13.2%. The linear ranges with R2 > 0.996 were 5-1000 ng mL-1 for basic analytes, and 20-1000 ng mL-1 for acidic analytes except diclofenac (1-1000 ng mL-1). The repeatability and accuracy at four levels were in the range of 3%-10% and 86%-120%, respectively. The limit of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) were found to be 0.07-0.49 ng mL-1 and 0.25-1.63 ng mL-1, respectively. Finally, the strategy for constructing a sLPME system was further confirmed with urine, plasma and saliva using another two versatile SLM solvents possessing high affinity to both acidic and basic analytes. Successive LPME enabled separation of acidic and basic analytes from the same sample under optimum extraction conditions for all target analytes. Thus, we believe that the sLPME system will become a potent platform for forensic toxicology analysis, food science, environmental analysis and epidemiology study.

Effect of sample matrices on supported liquid membrane: Efficient electromembrane extraction of cathinones from biological samples.

In this work, the effect of sample matrix on electromembrane extraction (EME) was investigated for the first time using cathinones (log P < 1.0) as polar basic model analytes. Ten supported liquid membranes (SLMs) were tested for EME from spiked buffer solutions, urine, and whole blood samples, respectively. For buffer solutions, SLMs containing aromatic solvents provided higher EME recovery than non-aromatic solvents, which confirmed the significance of cation-π interactions for EME of basic substances. Interestingly, when applied to urine and whole blood samples, aromatic SLMs were less efficient, while non-aromatic SLMs containing abundant hydrogen-bond acidity/basicity were efficient. These observations were explained by SLM fouling, and the antifouling property of the SLM was clearly dependent on the nature of the SLM solvent. Accordingly, a binary SLM containing aromatic 1-ethyl-2-nitrobenzene (ENB) and non-aromatic 1-undecanol (1:1 v/v) was developed. This binary SLM was not prone to fouling, and provided high recoveries of cathinones from urine and whole blood. EME based on this SLM was optimized and evaluated in combination with liquid chromatography tandem mass spectrometry (LC-MS/MS), and the linear ranges with R2 ≥ 0.9903 for cathinones in whole blood and urine were 5-200 ng/mL and 1-200 ng/mL, respectively. The LOD and LOQ of cathinones were ranged from 0.12 to 0.54 ng/mL and 0.38-1.78 ng/mL, respectively. The repeatability and accuracy bias at three levels were ≤11% and within 10%, respectively. In addition, the matrix effect ranged from 88% to 118% was also in compliance with guidelines for bioanalytical method validation provided by the European Medicines Agency.