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.

Electromembrane extraction of barbiturates using tributyl phosphate as an efficient supported liquid membrane.

In this fundamental work, tributyl phosphate (TBP) with zero hydrogen-bond acidity was for the first time discovered as an efficient supported liquid membrane (SLM) for EMEof acidic drugs (barbiturates) due to its high polarity-polarizability. This discovery indicated that strong dipole-dipole interaction induced by high polarity-polarizability played an important role for efficient EME of acidic drugs. In addition, three barbiturates were successfully extracted for the first time from human whole blood and urine samples by EME with recoveries up to 90%. Interestingly, efficient EME of barbiturates from biological samples required much lower extraction voltage than that from buffer samples. This was due to the significant contribution from LPME during the EME process, when EME was conducted from the samples with just partially ionized analytes. EME combined with HPLC-UV and LC-MS were validated using whole blood and urine, respectively. In all cases, the linearity (R2) was >0.99 within the reported linear range. Repeatability at three concentrations was satisfactory (<12%), and the limits of detection (LOD, S/N = 3) were in the ranges of 0.44-4.30 ng mL-1 and 0.14-0.69 µg mL-1 for EME-LC-MS and EME-HPLC-UV, respectively. Finally, the validated methods were successfully applied for the identification and quantification of barbiturates in whole blood and urine samples for a forensic case, indicating that EME could be used in routine toxicological analysis. Thus, we believe that EME has great potential as a green, efficient and alternative sample preparation method not only in the field of analytical chemistry but also in the fields of forensic science and clinical medicine.

Electromembrane extraction of chlorprothixene, haloperidol and risperidone from whole blood and urine.

Separation of antipsychotic drugs from whole blood and urine is of great importance for clinic and forensic laboratories. In this work, chlorprothixene, haloperidol and risperidone representing the first and second generations of antipsychotic drugs were studied. Among them, chlorprothixene and risperidone were investigated for the first time by electromembrane extraction (EME). After the screening, 2-nitrophenyl octyl ether (NPOE) was used as the supported liquid membrane (SLM). The EME performance for spiked water (pH 2), whole blood and urine was tested and optimized individually. Using NPOE and 60 V, efficient EME was achieved from urine and whole blood with trifluoroacetic acid as the acceptor solution. The equilibrium time required for EME was dependent on the sample matrices. The steady-state of EME was reached in 30 min and 20 min for whole blood and urine, respectively. At steady-state, the EME recoveries of the targets from different sample matrices were satisfactory, and were in the range of 74%-100%. The proposed EME approach combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was evaluated using whole blood and urine. The obtained linearity was 1-200 ng mL-1, and the coefficient of determination (R2) was ≥ 0.9853 for haloperidol and ≥ 0.9936 for chlorprothixene and risperidone. The limit of detection (LOD) and accuracy for all the targets ranged from 0.2-0.6 ng mL-1 and 102%-110%, respectively, and the repeatability at low (1 ng mL-1), medium (10 ng mL-1) and high (200 ng mL-1) concentration was ≤ 12% (RSD). Finally, the validated approach was successfully used to determine chlorprothixene, risperidone and haloperidol in whole blood and urine from rats, which were treated with chlorprothixene, risperidone and haloperidol at low therapeutic dose, respectively.

Liquid-Phase Microextraction or Electromembrane Extraction?

Isolation of substances by liquid-phase microextraction (LPME) or electromembrane extraction (EME) is becoming more and more important in analytical chemistry. However, the understanding of the mass transfer in LPME and EME is limited, especially for highly concentrated samples. In this work, the mass transfer in LPME and EME from aqueous samples (0.5-200 mg L-1) was studied in terms of recovery, equilibrium time, flux, and mass transfer capacity. In both EME and LPME, high recoveries were achieved at low analyte concentration, and the recoveries decreased at high analyte concentration. For EME, the loss in recovery was partly compensated by increasing the extraction voltage (from 50 to 200 V), while the LPME recovery at high analyte concentration was improved by increasing the extraction time (from 30 to 180 min). EME was superior in terms of equilibrium time and flux, while LPME provided much higher mass transfer capacity especially for highly concentrated samples. Moreover, the recovery was much more sensitive to high analyte concentrations in EME than in LPME, and the EME recovery decreased significantly above 50 mg L-1, indicating that LPME could be used to isolate analytes in a wider concentration range than EME. We believe that this fundamental study will be of great importance for the selection of a suitable membrane-based microextraction technique.

Determination of Barbiturates in Biological Specimens by Flat Membrane-Based Liquid-Phase Microextraction and Liquid Chromatography-Mass Spectrometry.

The wide abuse of barbiturates has aroused extensive public concern. Therefore, the determination of such drugs is becoming essential in therapeutic drug monitoring and forensic science. Herein, a simple, efficient, and inexpensive sample preparation technique, namely, flat membrane-based liquid-phase microextraction (FM-LPME) followed by liquid chromatography-mass spectrometry (LC-MS), was used to determine barbiturates in biological specimens. Factors that may influence the efficiency including organic extraction solvent, pH, and composition of donor and acceptor phases, extraction time, and salt addition to the sample (donor phase) were investigated and optimized. Under the optimized extraction conditions, the linear ranges of the proposed FM-LPME/LC-MS method (with correlation coefficient factors ≥ 0.99) were 7.5-750 ng mL-1 for whole blood, 5.0-500 ng mL-1 for urine, and 25-2500 ng g-1 for liver. Repeatability between 5.0 and 13.7% was obtained and the limit of detection (LOD) values ranged from 1.5 to 3.1 ng mL-1, from 0.6 to 3.6 ng mL-1, and from 5.2 to 10.0 ng g-1 for whole blood, urine, and liver samples, respectively. This method was successfully applied for the analysis of barbiturates in blood and liver from rats treated with these drugs, and excellent sample cleanup was achieved.