Shu-g Lin

Determination of phenylurea herbicides in aqueous samples using partitioned dispersive liquid–liquid microextraction

Partitioned dispersive liquid-liquid microextraction (PDLLME), using THF as the dispersive solvent and dichloromethane as the extraction solvent, was utilized to isolate and concentrate phenylurea herbicides (PUHs) from aqueous samples. In PDLLME, a dispersive solvent should be able to partition in the organic extractant droplets to effectively extract the polar organic compounds from aqueous samples. The mixture of the water-immiscible extractant and the partitioned dispersive solvent was obtained by centrifugation, dried under low pressure, reconstituted in methanol-water mixture (1:1), and injected into a HPLC system for the determination of PUHs. The enrichment factors of the PUHs ranged from 68 to 126 under the optimal conditions. The linear range was 0.5-100 ng ml(-1) for each analyte, the relative standard deviations of PUHs were in the range of 1.5-5.9% (n=5), and the detection limits (signal-to-noise ratio of 3) ranged from 0.10 to 0.28 ng ml(-1) for the herbicides. The range of intraday precision (n=5) for PUHs at the levels of 0.5, 5, and 50 ng ml(-1) were 3.0-5.9%, 1.8-3.3%, and 2.2-3.6%, respectively. The range of interday precision (n=5) at 0.5, 5, and 50 ng ml(-1) were 0.4-1.8%, 1.2-2.4%, and 0.9-2.3%, respectively. The recoveries of PUHs from three spiked river water samples, at a level of 10 ng ml(-1), were 91.2-104.1%. Due to its rapidity, ease of operation, and high recovery, PDLLME can be utilized to isolate and concentrate organic environmental contaminants such as PUHs from aqueous samples.

Microfluidic chip-based liquid chromatography coupled to mass spectrometry for determination of small molecules in bioanalytical applications.

The development and integration of microfabricated liquid chromatography (LC) microchips have increased dramatically in the last decade due to the needs of enhanced sensitivity and rapid analysis as well as the rising concern on reducing environmental impacts of chemicals used in various types of chemical and biochemical analyses. Recent development of microfluidic chip‐based LC mass spectrometry (chip‐based LC‐MS) has played an important role in proteomic research for high throughput analysis. To date, the use of chip‐based LC‐MS for determination of small molecules, such as biomarkers, active pharmaceutical ingredients (APIs), and drugs of abuse and their metabolites, in clinical and pharmaceutical applications has not been thoroughly investigated. This mini‐review summarizes the utilization of commercial chip‐based LC‐MS systems for determination of small molecules in bioanalytical applications, including drug metabolites and disease/tumor‐associated biomarkers in clinical samples as well as adsorption, distribution, metabolism, and excretion studies of APIs in drug discovery and development. The different types of commercial chip‐based interfaces for LC‐MS analysis are discussed first and followed by applications of chip‐based LC‐MS on biological samples as well as the comparison with other LC‐MS techniques.

Orthogonal array optimization of ultrasound-assisted emulsification-microextraction for the determination of chlorinated phenoxyacetic acids in river water.

Orthogonal array design (OAD) was utilized for the first time to optimize the experimental conditions of ultrasound-assisted emulsification-microextraction (USAEME) for determining chlorinated phenoxyacetic acids (CPAs) in river water samples. The use of ultrasound facilitates the mass transfer of CPAs from an aqueous phase into a water-immiscible organic extraction solvent (dichloromethane, DCM) without adding dispersive solvent to form numerous microdroplets. The water-immiscible extractant was collected by centrifugation, dried under low pressure, reconstituted in methanol-water mixture (1:1), and injected into a HPLC system for the determination of CPAs. The linear range was 2-1000 ng mL(-1) (2, 5, 10, 50, 200, 500 and 1000 ng mL(-1)) for each analyte and the relative standard deviations of CPAs among the seven different concentrations were in the range of 1.5-17.0% (n=3). The detection limits (signal-to-noise ratio of 3) of CPAs ranged from 0.67 to 1.50 ng mL(-1). The ranges of intra-day precision (n=3) for CPAs at the levels of 5 and 200 ng mL(-1) were 3.6-11.9% and 5.3-9.5%, respectively. The range of inter-day precision (n=3) at 5 and 200 ng mL(-1) were 1.4-7.7% and 8.5-12.2%, respectively. The applicability of USAEME for environmental analysis was demonstrated by determining CPAs in river water. The recoveries of CPAs from five-spiked river water samples at 10 and 200 ng mL(-1) were 96.3-112.5% and 94.8-109.4%, respectively. The maximum contaminant level (MCL) of 2,4-D in drinking water and the tolerance of residues in food for p-CPA are 70 and 200 microg L(-1), respectively, according to the US EPA regulations. These contaminant levels fall in the linear range investigated in this study. In addition, this USAEME method provided detection limits lower than their contaminant levels, which made USAEME an effective sample preparation method for determining organic environmental contaminants, such as CPAs, in river water samples with little consumption of organic solvent.

Determination of chloramphenicol, thiamphenicol and florfenicol in milk and honey using modified QuEChERS extraction coupled with polymeric monolith-based capillary liquid chromatography tandem mass spectrometry.

A poly(lauryl methacrylate-co-methacrylic acid-co-ethylene glycol dimethacrylate) [LMA-MAA-EDMA] monolithic column was used to simultaneously determine amphenicol antibiotics (chloramphenicol/CAP, thiamphenicol/TAP, and florfenicol/FF) in milk and honey samples by capillary liquid chromatography tandem mass spectrometry (LC-MS/MS). QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was optimized for sample pretreatment. Good linearity (0.1-15 ng g(-1)) and extraction recoveries (95.8-100.2% and 95.6-99.3% for milk and honey samples, respectively; n=3) with minor matrix effect (≦ 5% ion suppression) were obtained. Limits of detection were estimated at 0.02-0.045 ng g(-1). Good intra-day/inter-day precision (0.2-9.1%/0.3-8.7%) and accuracy (90.5-110.0%/93.4-109.3%) were achieved. With more than 200 analyses of real samples, no noticeable carry-over and deterioration of separation efficiency were observed using the monolithic column. The applicability of the developed QuEChERS-capillary LC-MS/MS method was demonstrated by determining the occurrence of CAP, TAP, and FF in various milk and honey samples.

Quantitative determination of 8-isoprostaglandin F2α in human urine using microfluidic chip-based nano-liquid chromatography with on-chip sample enrichment and tandem mass spectrometry

Urinary 8-isoprostaglandin F(2α) (8-isoPGF(2α)) has been reported as an important biomarker to indicate the oxidative stress status in vivo. In order to quantitatively determine the low contents of 8-isoPGF(2α) (in sub- to low ng mL(-1) range) in physiological fluids, a sensitive detection method has become an important issue. In this study, we employed a microfluidic chip-based nano liquid chromatography (chip-nanoLC) with on-chip sample enrichment coupled to triple quadrupole mass spectrometer (QqQ-MS) for the quantitative determination of 8-isoPGF(2α) in human urine. This chip-nanoLC unit integrates a microfluidic switch, a chip column design having a pre-column (enrichment column) for sample enrichment prior to an analytical column for separation, as well as a nanospray emitter on a single polyimide chip. The introduction of enrichment column offers the advantages of online sample pre-concentration and reducing matrix influence on MS detection to improve sensitivity. In this study, the chip-nanoLC consisting of Zorbax 300A SB-C18 columns and Agilent QqQ Mass spectrometer were used for determining 8-isoPGF(2α) in human urine. Gradient elution was employed for effective LC separation and multiple reaction monitoring (MRM) was utilized for the quantitative determination of 8-isoPGF(2α) (m/z 353→193). We employed liquid-liquid extraction (LLE)/solid-phase extraction (SPE) for extracting analyte and reducing matrix effect from urine sample prior to chip-nanoLC/QqQ-MS analysis for determining urinary 8-isoPGF(2α). Good recoveries were found to be in the range of 83.0-85.3%. The linear range was 0.01-2 ng mL(-1) for urinary 8-isoPGF(2α). In addition, the proposed method showed good precision and accuracy for 8-isoPGF(2α) spiked synthetic urine samples. Intra-day and inter-day precisions were 1.8-5.0% and 4.3-5.8%, respectively. The method accuracy for intra-day and inter-day assays ranged from 99.3 to 99.9% and 99.4 to 99.7%, respectively. Due to its rapidity, enhanced sensitivity, and high recovery, this chip-nanoLC/QqQ-MS system was successfully utilized to determine the physiological biomarkers such as 8-isoPGF(2α) in human urine for clinical diagnosis.

Preparation and evaluation of poly(alkyl methacrylate-co-methacrylic acid-co-ethylene dimethacrylate) monolithic columns for separating polar small molecules by capillary liquid chromatography

In this study, methacrylic acid (MAA) was incorporated with alkyl methacrylates to increase the hydrophilicity of the synthesized ethylene dimethacrylate-based (EDMA-based) monoliths for separating polar small molecules by capillary LC analysis. Different alkyl methacrylate-MAA ratios were investigated to prepare a series of 30% alkyl methacrylate-MAA-EDMA monoliths in fused-silica capillaries (250-μm i.d.). The porosity, permeability, and column efficiency of the synthesized MAA-incorporated monolithic columns were characterized. A mixture of phenol derivatives is employed to evaluate the applicability of using the prepared monolithic columns for separating small molecules. Fast separation of six phenol derivatives was achieved in 5 min with gradient elution using the selected poly(lauryl methacrylate-co-MAA-co-EDMA) monolithic column. In addition, the effect of acetonitrile content in mobile phase on retention factor and plate height as well as the plate height-flow velocity curves were also investigated to further examine the performance of the selected poly(lauryl methacrylate-co-MAA-co-EDMA) monolithic column. Moreover, the applicability of prepared polymer-based monolithic column for potential food safety applications was also demonstrated by analyzing five aflatoxins and three phenicol antibiotics using the selected poly(lauryl methacrylate-co-MAA-co-EDMA) monolithic column.

Microfluidic chip-based liquid chromatography coupled to mass spectrometry for determination of small molecules in bioanalytical applications: An update: Liquid Phase Separations

Many microfluidic chip‐based LC‐MS systems have been utilized for high‐throughput analysis in various fields of bioanalytical applications such as proteomic, glycomic, pharmaceutical, and clinical research. This review is an update of a previous review article (Electrophoresis 2012, 33, 635–643) to mainly cover the most recent advancements in chip‐based LC‐MS for determining small molecules in bioanalysis. First, the different types of microfluidic chip devices for chip‐based LC‐MS analysis will be discussed. Following the discussion of the recent developments in the chip‐based instrumentation, the applications of chip‐based LC‐MS for determining small molecules, such as glycans, pharmaceutical drugs, drugs of abuse, drug metabolites, and biomarkers in various biological sample matrixes will also be included in this review.

Microfluidic chip-based nano-liquid chromatography tandem mass spectrometry for quantification of aflatoxins in peanut products

Aflatoxins (AFs), a group of mycotoxins, are generally produced by fungi Aspergillus species. The naturally occurring AFs including AFB1, AFB2, AFG1, and AFG2 have been clarified as group 1 human carcinogen by International Agency for Research on Cancer. Developing a sensitive analytical method has become an important issue to accurately quantify trace amount of AFs in foodstuffs. In this study, we employed a microfluidic chip-based nano LC (chip-nanoLC) coupled to triple quadrupole mass spectrometer (QqQ-MS) system for the quantitative determination of AFs in peanuts and related products. Gradient elution and multiple reaction monitoring were utilized for chromatographic separation and MS measurements. Solvent extraction followed by immunoaffinity solid-phase extraction was employed to isolate analytes and reduce matrix effect from sample prior to chip-nanoLC/QqQ-MS analysis. Good recoveries were found to be in the range of 90.8%-100.4%. The linear range was 0.048-16 ng g(-1) for AFB1, AFB2, AFG1, AFG2 and AFM1. Limits of detection were estimated as 0.004-0.008 ng g(-1). Good intra-day/inter-day precision (2.3%-9.5%/2.3%-6.6%) and accuracy (96.1%-105.7%/95.5%-104.9%) were obtained. The applicability of this newly developed chip-nanoLC/QqQ-MS method was demonstrated by determining the AFs in various peanut products purchased from local markets.

Recent developments in microfluidic chip-based separation devices coupled to MS for bioanalysis.

In recent years, the development of microfluidic chip separation devices coupled to MS has dramatically increased for high-throughput bioanalysis. In this review, advances in different types of microfluidic chip separation devices, such as electrophoresis- and LC-based microchips, as well as 2D design of microfluidic chip-based separation devices will be discussed. In addition, the utilization of chip-based separation devices coupled to MS for analyzing peptides/proteins, glycans, drug metabolites and biomarkers for various bioanalytical applications will be evaluated.

Quantitative determination of perchlorate in bottled water and tea with online solid phase extraction high-performance liquid chromatography coupled to tandem mass spectrometry.

Due to the similarity in ionic radius, perchlorate has been reported to inhibit the iodide intake in the thyroid gland, which may lead to low heart rate, weight gain, and fatigue. In recent years, the presence of perchlorate in drinking water, surface water, soil, and food supplies in the United States has raised a great concern on establishing the maximum residue limit (MRL) for perchlorate to reduce its possible adverse influence on human health. US EPA currently puts perchlorate on the final third Contamination Candidate List (CCL3) and suggests a health reference level at 4.9 μg L⁻¹. The MRL of perchlorate was therefore set at 5.0 μg L⁻¹ by the authors for method validation. In this study, large volume injection (up to 1-mL) and online solid phase extraction (SPE) were utilized for pre-concentrating perchlorate ions and removing unretained matrix components prior to reversed-phase HPLC analysis using ESI-tandem MS under the negative mode. After eluting perchlorate from online SPE, 0.1% formic acid solution was utilized for isocratic HPLC analysis without any organic solvent. Multiple reaction monitoring (MRM) and the internal standard, Cl₁₈O₄⁻, were utilized for quantitatively determining perchlorate in bottled water and bottled tea samples. Two linear ranges, 0.05-0.50 μg L⁻¹ and 0.50-10.00 μg L⁻¹, were established to better estimate the residual amounts of perchlorate in bottled water samples with a method detection limit (MDL, signal-to-noise ratio of 3) of 0.01 μg L⁻¹. The linear range was 1.50-10.00 μg L⁻¹ for bottled tea samples with a MDL of 0.5 μg L⁻¹. In addition, the proposed method was further validated based on the EU Commission Decision 2002/657/EC, including within-laboratory reproducibility, decision limit (CCα), and detection capability (CCβ) for bottled water and bottled tea samples. The intra-day/inter-day precision and accuracy as well as within-laboratory reproducibility were determined by calculating the relative standard deviation (RSD) at three spiked levels (0.5 MRL, 1 MRL, 1.5 MRL). The within-laboratory reproducibility (n=18) for both bottled water and bottled tea samples, spiked at MRL (5.0 μg L⁻¹) of ClO₄⁻, was less than 10%. The values of CCα/CCβ were reported as 5.43/5.74 μg L⁻¹ and 5.03/5.75 μg L⁻¹ for bottled water and bottled tea samples, respectively.