Simultaneous determination of nitrate and nitrite in vegetables by poly(vinylimidazole-co-ethylene dimethacrylate) monolithic capillary liquid chromatography with UV detection.

Simultaneous determination of nitrate (NO3‾) and nitrite (NO2‾) in vegetables was performed on a poly(1-vinylimidazole-co-ethylene dimethacrylate) (VIM-EDMA) monolithic column by capillary liquid chromatography (LC) with UV detection. Good linearity (0.5-100 µg mL-1 i.e. 12.5 -2500 µg g-1 in vegetables) was obtained with coefficient of determination > 0.996. Limits of detection (signal-to-noise ratio: S/N= 3) were estimated at 0.06 and 0.05 µg mL-1, which corresponded to 1.50 and 1.25 µg g-1 for NO2‾ and NO3‾, respectively, in vegetables. The limits of quantification (S/N= 10) were estimated at 0.17 and 0.16 µg mL-1 (4.25 and 4.00 µg g-1 in vegetables) for NO2‾ and NO3‾, respectively. Although the detection limits were relatively higher than other LC-UV techniques, this proposed method offered satisfactory sensitivity for complying the Acceptable Daily Intake (ADI) levels set by EU to monitor the occurrence of NO2‾ and NO3‾in vegetables. The intra-day/inter-day precision (0.14-3.35%/0.06-6.93%) and accuracy (90.33-103.32%/96.00-101.26%) were also examined for method validation. No obvious carry-over and decline of separation efficiency were observed for more than 200 analyses of real samples. The occurrence of NO2‾ and NO3‾in various vegetable samples was investigated to demonstrate the potential of utilizing the developed polymeric monolith-based capillary LC-UV method for food safety application.

Separation of inorganic anions by capillary ion chromatography with UV detection using poly(vinylimidazole-co-ethylene dimethacrylate) monolithic column.

Poly(1-vinylimidazole-co-ethylene dimethacrylate) (VIM-EDMA) monolithic stationary phase was applied for separation of inorganic anions by capillary ion chromatography (IC). The retention of inorganic anions on the VIM-EDMA column was investigated using various salt solutions as the eluent. Good separation of inorganic anions was obtained on VIM-EDMA monolithic column using NH4Cl as the eluent. Good mechanical stability and low swelling propensity values (0.12 and -0.02 for ACN and MeOH, respectively) were obtained. The column repeatability was also examined by determining the relative standard deviations (RSDs) of retention time and peak area of target anions. Relatively low RSDs (n = 7) of retention time (<2.3%) and peak area (<8.8%) were obtained on the VIM-EDMA column. The utilization of VIM-EDMA column for potential environmental application was also demonstrated by determining the occurrence of inorganic anions in various environmental water samples without sample preparation process.

Preparation and characterization of vinylimidazole-based polymer monolithic stationary phases for reversed-phase and hydrophilic interaction capillary liquid chromatography.

In this study, we applied 1-vinylimidazole (VIM) as the functional monomer to prepare a series of VIM-based monolithic stationary phases for both reversed-phase and hydrophilic interaction capillary liquid chromatography (LC) using various dimethacrylates (EDMA: ethylene dimethacrylate; HDDMA: 1,6-hexanediol dimethacrylate; DDDMA: 1,10-decanediol dimethacrylate) as cross-linkers. With a simple thermally initiated free-radical cross-linking polymerization process, VIM-based monolithic stationary phases have been successfully prepared. The porosity, permeability, and column efficiency of synthesized VIM-based monolithic stationary phases were characterized. With similar total porosity (85-90%), the VIM-HDDMA monoliths showed the lowest permeability among the three sets of VIM-based stationary phases. Various sets of non-polar (alkyl benzenes and polycyclic aromatic hydrocarbons) and polar analytes (phenol derivatives and amphenicol antibiotics) were applied as model compounds to further investigate the retention behavior of the VIM-based monolithic stationary phases for reversed-phase capillary LC analysis using selected VIM-based monolithic columns. While a mixture of organic acids was employed to perform HILIC analysis using the selected VIM-based monolithic columns. The separation selectivity and retention behavior of the VIM-based monolithic stationary phases were compared to those obtained using three previously prepared alkyl methacrylate-based monolithic columns. Strong retention and good resolution of polar analytes (such as phenol derivatives, amphenicol antibiotics, and organic acids) were observed using the selected VIM-based monolithic columns. The strong retention and good resolution might be attributed to the additional hydrogen-bonding between the hydrogen-donating analytes and the hydrogen-accepting imidazolium functionality on the VIM-based stationary phase. The applicability for both reversed-phase and HILIC capillary LC analysis has also been demonstrated using the selected VIM-based monolithic columns.

Quantification of 7-aminoflunitrazepam in human urine by polymeric monolith-based capillary liquid chromatography coupled to tandem mass spectrometry.

Using a simple liquid-liquid extraction (LLE) procedure for sample pretreatment, 7-Aminoflunitrazepam (7-aminoFM2), a major metabolite of flunitrazepam (FM2), was determined in urine samples by polymeric monolith-based capillary liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The linearity was found in the range of 0.1-50ngmL-1 with a method detection limit (signal-to-noise ratio of 3) estimated at 0.05ngmL-1. Using the proposed method, good precision and recovery were also found in spiked urine samples at the levels of 0.5, 5.0, and 50ngmL-1 (intra-day/inter-day precision: 0.6-1.8% / 0.1-0.8%; post-spiked/pre-spiked recovery: 95.4-102.9% / 96.3-102.5%). In addition, acceptable relative differences (-24.2 - 0.8%) were observed by analyzing clinical urine samples using this monolith-based capillary LC-MS/MS method compared with the results obtained by the routine GC-MC method. Using the monolithic column, no noticeable deterioration of separation efficiency or carry-over was observed for more than 200 injections of urine samples. The applicability of the developed monolith-based capillary LC-MS/MS method was demonstrated by quantifying 7-aminoFM2 in various clinical urine samples. Based on these experimental results, the proposed LLE-monolith-based capillary LC-MS/MS method shows the potential for routine determination of drug metabolites in human urine for clinical and forensic applications.

Determination of sulfonamides in animal tissues by modified QuEChERS and liquid chromatography tandem mass spectrometry.

In this study, the salting-out solvent extraction and dispersive solid-phase extraction (dSPE) clean-up steps in QuEChERS (quick, easy, cheap, effective, rugged, and safe) method were optimized to reduce matrix effect and efficiently extract target sulfonamides from a variety of edible animal tissues. The extracted sulfonamides were then analyzed using liquid chromatography tandem mass spectrometry (LC-MS/MS). Good extraction recoveries (74.0-100.3% in five different sources of animal tissues; n=3) with acceptable matrix effect (<10%, except for liver samples) were obtained using the proposed method. For the first time, a commercial ND-lipids cartridge was used to remove hydrophobic matrix components from fat-rich animal tissues in the clean-up step of QuEChERS. In addition, good linearity (0.125-12.5ngg-1) was observed using matrix-matched calibration (in beef). Limits of detection (LODs) were estimated at 0.01-0.03ngg-1 in beef, pork, and chicken samples. For beef tripe and pig liver samples, the LODs were in the range of 0.02-0.04ngg-1. Good intra-day/inter-day precision (1.0-10.5%/0.4-8.0%) and accuracy (95.2-107.2%/97.8-102.1%) were also achieved using the modified QuEChERS for sample pretreatment. The applicability of the modified QuEChERS-LC-MS/MS method was demonstrated by determining the occurrence of target sulfonamides in various edible animal tissues for potential food safety analysis.

Chromatographic selectivity of poly(alkyl methacrylate-co-divinylbenzene) monolithic columns for polar aromatic compounds by pressure-driven capillary liquid chromatography.

In this study, divinylbenzene (DVB) was used as the cross-linker to prepare alkyl methacrylate (AlMA) monoliths for incorporating π-π interactions between the aromatic analytes and AlMA-DVB monolithic stationary phases in capillary LC analysis. Various AlMA/DVB ratios were investigated to prepare a series of 30% AlMA-DVB monolithic stationary phases in fused-silica capillaries (250-µm i.d.). The physical properties (such as porosity, permeability, and column efficiency) of the synthesized AlMA-DVB monolithic columns were investigated for characterization. Isocratic elution of phenol derivatives was first employed to evaluate the suitability of the prepared AlMA-DVB columns for small molecule separation. The run-to-run (0.16-1.20%, RSD; n = 3) and column-to-column (0.26-2.95%, RSD; n = 3) repeatabilities on retention times were also examined using the selected AlMA-DVB monolithic columns. The π-π interactions between the aromatic ring and the DVB-based stationary phase offered better recognition on polar analytes with aromatic moieties, which resulted in better separation resolution of aromatic analytes on the AlMA-DVB monolithic columns. In order to demonstrate the capability of potential environmental and/or food safety applications, eight phenylurea herbicides with single benzene ring and seven sulfonamide antibiotics with polyaromatic moieties were analyzed using the selected AlMA-DVB monolithic columns.

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.

Polymer monolith microextraction using poly(butyl methacrylate-co-1,6-hexanediol ethoxylate diacrylate) monolithic sorbent for determination of phenylurea herbicides in water samples.

In this study, recently developed 1,6-hexanediol ethoxylate diacrylate (HEDA)-based polymeric monoliths were utilized as sorbents for efficient extraction of phenylurea herbicides (PUHs) from water samples. The HEDA-based monolithic sorbents were prepared in a fused silica capillary (0.7mm i.d., 4.5-cm long) for polymer monolith microextraction (PMME). The experimental parameters of PMME microextraction including sample loading speed, pH of sample solution, composition of elution solvent, and addition of salt were optimized to efficiently extract PUHs from environmental water samples. The extracted PUHs were determined using ultra-high performance liquid chromatography (UHPLC) with UV-photodiode array detection. The extraction recoveries for PUHs-spiked water samples were 91.1-108.1% with relative standard deviations lower than 5%. The linearity range was 0.025-25ngmL(-1) for each PUH and the detection limits of PUHs were estimated at 0.006-0.019ng mL(-1). In addition, good intra-day/inter-day precision (0.1-8.7%/0.2-8.9%) and accuracy (92.0-108.0%/96.5-105.2%) of the proposed method were obtained. The extraction capacity of the monolith-filled capillary was also determined to be approximately 1µg. Moreover, each monolith-filled capillary could be reused up to 8 times without carry-over. According to the European Union regulations, the allowed permissible limit of any single herbicide in drinking water is 0.1ng mL(-1). This permissible level fell in the linear range examined in this study. In addition, the proposed method provided detection limits lower than the allowed permissible level, which demonstrated the feasibility of utilizing the HEDA-based monolithic sorbent to perform PMME for determining contaminants, such as PUHs, in environmental application.

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.

Beyond dispersive liquid-liquid microextraction.

Dispersive liquid-liquid microextraction (DLLME) and other dispersion liquid-phase microextraction (LPME) methods have been developed since the first DLLME method was reported in 2006. DLLME is simple, rapid, and affords high enrichment factor, this is due to the large contact surface area of the extraction solvent. DLLME is a method suitable for the extraction in many different water samples, but it requires using chlorinated solvents. In recent years, interest in DLLME or dispersion LPME has been focused on the use of low-toxicity solvents and more conveniently practical procedures. This review examines some of the most interesting developments in the past few years. In the first section, DLLME methods are separated in two categories: DLLME with low-density extraction solvent and DLLME with high-density extraction solvent. Besides these methods, many novel special devices for collecting low-density extraction solvent are also mentioned. In addition, various dispersion techniques with LPME, including manual shaking, air-assisted LPME (aspirating and injecting the extraction mixture by syringe), ultrasound-assisted emulsification, vortex-assisted emulsification, surfactant-assisted emulsification, and microwave-assisted emulsification are described. Besides the above methods, combinations of DLLME with other extraction techniques (solid-phase extraction, stir bar sorptive extraction, molecularly imprinted matrix solid-phase dispersion and supercritical fluid extraction) are introduced. The combination of nanotechnique with DLLME is also introduced. Furthermore, this review illustrates the application of DLLME or dispersion LPME methods to separate and preconcentrate various organic analytes, inorganic analytes, and samples.

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

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.

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.

Preparation and evaluation of 1,6-hexanediol ethoxylate diacrylate-based alkyl methacrylate monolithic capillary column for separating small molecules.

Due to the high porosity, good thermal stability, and good physical stability at high pressure, polymer monoliths have been successfully utilized as the stationary phases for capillary liquid chromatography (LC) analysis. In this study, we introduced 1,6-hexanediol ethoxylate diacrylate (HEDA) as a cross-linker to prepare alkyl methacrylate monoliths for efficient separation of polar small molecules. HEDA provided additional dipole-dipole interactions between the monolithic stationary phases and polar analytes. For comparison, ethylene dimethacrylate and 1,6-hexanediol dimethacrylate were also utilized as cross-linkers to prepare alkyl methacrylate monoliths. A series of alkyl methacrylate polymeric monoliths were synthesized in fused-silica capillaries using the three different cross-linkers. The porosity, permeability and column efficiency of the synthesized alkyl methacrylate monoliths were characterized. A mixture of phenol derivatives was employed to evaluate the applicability of the prepared monolithic columns for separating small molecules using capillary LC. The HEDA-based alkyl methacrylate monoliths offered the most efficient chromatographic separation for phenol derivatives. Moreover, the capability of applying the novel HEDA-based alkyl methacrylate monolithic columns for potential environmental analysis was demonstrated by separating eight phenylurea herbicides.

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.

Determination of endocrine-disrupting phenols in water samples by a new manual shaking-enhanced, ultrasound-assisted emulsification microextraction method.

Manual shaking-enhanced, ultrasound-assisted emulsification microextraction (MS-USAEME) combined with ultraperformance liquid chromatography (UPLC) with UV detection has been developed for the determination of five endocrine-disrupting phenols (EDPs) in seawater samples and detergent samples: 4-tert-butylphenol (4-t-BP), 4-cumylphenol (4-CP), 4-tert-octylphenol (4-t-OP), 2,4-di-tert-butylphenol (2,4-di-t-BP) and 4-nonylphenol (4-NP). Optimum conditions were found to be: 25 µL 1-bromohexadecane as extraction solvent, 5 mL of aqueous sample and 1 g of NaCl to control the ionic strength; manual shaking for 10 s; ultrasonication for 1 min; centrifugation for 3 min at 5000 rpm (speed). For MS-USAEME, manual shaking for 10 s is essential for effective extraction when the ultrasonic extraction time is as brief as 1 min. The small volume of aqueous sample enhances the effect of manual shaking significantly. For seawater samples, the limit of detection (LOD) was 0.5-2.8 ng mL(-1), the limit of quantification (LOQ) was 1.8-9.3 ng mL(-1) with the relative standard deviation (RSD) in the range 4.2-10.3%. For detergent samples, the LOD was 0.4-2.4 ng mL(-1), LOQ was 1.6-8.2 ng mL(-1) and RSD 4.7-10.0%. The relative recovery was 96-109% for seawater samples and 81-106% for the detergent 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.

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 (CCß) 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/CCß 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.

Nanoparticle-assisted MALDI-TOF MS combined with seed-layer surface preparation for quantification of small molecules.

Despite the advantages of simplicity and high-throughput detection that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has over other methods, quantitative analysis of low-molecular-weight analyte is hampered by interference from matrix-derived background noise and signal fluctuation due to the inhomogeneous MALDI sample surface. Taking advantage of improved sample homogeneity through matrix-conjugated magnetic nanoparticles (matrix@MNP) and the seed-layer method, we report a new strategy for the rapid identification and quantification of drugs in urine samples, using morphine and 7-aminoflunitrazepam (7-aminoFM2) as model compounds. To our knowledge, this is the first attempt using the seed-layer method for small molecule analysis. By applying the proposed seed-layer method, which was specifically optimized for the 2,5-dihydroxybenzoic acid@MNP (DHB@MNP) matrix, homogeneous sample crystallization examined by microscopy analysis was obtained that generated reproducible MALDI signals (RSD<10.0%). For urine sample analysis, simple liquid-liquid extraction as a sample pretreatment step effectively reduced the ion suppression effect caused by the endogenous components in urine; good recoveries (82-90%) were obtained with a small ion suppression effect (<14% of signal decrease). This newly developed method demonstrated good quantitation linearity over a range of 50-2000 ng mL(-1) (R(2)>0.996) with reduced signal variation (RSD<10.0%). The detection limit is 30 ng mL(-1) with good precision (intra-day, 2.0-9.3%; inter-day, 5.0-10.0%) and accuracy (intra-day, 95.0-106.0%; inter-day, 103.0-115.5%). The nanoparticle-assisted MALDI-TOF MS combined with seed-layer surface preparation provides a rapid, efficient and accurate platform for the quantification of small molecules in urine samples.

Application of liquid-liquid-liquid microextraction and high-performance liquid chromatography for the determination of alkylphenols and bisphenol-A in water.

A method termed liquid-liquid-liquid microextraction (LLLME) was utilized to extract 4-t-butylphenol, 4-t-octylphenol, 4-n-nonylphenol, and bisphenol-A from water. The extracted target analytes were separated and quantified by high-performance liquid chromatography using a fluorescence detector. In LLLME, the donor phase (i.e. water sample) was made weakly acidic by adding monobasic potassium phosphate (KH(2) PO(4)); the organic phase adopted was 4-chlorotoluene; the acceptor phase (i.e. enriched extract) was 0.2 M tetraethylammonium hydroxide dissolved in ethylene glycol. This study solves a problem associated with the surface activity of long-chain alkylphenolate ions, permitting LLLME to extract long-chain alkylphenols. Experimental conditions such as acceptor phase composition, organic phase identity, acceptor phase volume, sample agitation, extraction time, and salt addition were optimized. The relative standard deviation (RSD, 2.0-5.8%), coefficient of determination (r(2) 0.9977-0.9999), and detection limit (0.017-0.0048 ng/mL) of the proposed method were achieved under the selected optimized conditions. The method was successfully applied to analyses of lake and tap water samples, and the relative recoveries of target analytes from the spiked lake and tap water samples were 92.8-106.3 and 93.6-105.6%, respectively. The results obtained with the proposed method confirm this microextraction technique to be reliable for the monitoring of alkylphenols and bisphenol-A in water samples.

Determination of phenoxyacetic acids and chlorophenols in aqueous samples by dynamic liquid-liquid-liquid microextraction with ion-pair liquid chromatography.

Dynamic liquid-liquid-liquid microextraction coupled with ion-pair liquid chromatography (IP-LC) and photodiode array detection was developed and used for the extraction and analysis of chlorinated phenoxyacetic acids (CPAs) and chlorophenols (CPs) from water samples. An organic extraction solvent mixture was chosen to simultaneously and effectively extract both CPAs and CPs from aqueous samples. The method detection limit (MDL) ranged from 0.06 to 0.45 µg L(-1) with good reproducibility. The relative standard deviations were in the range of 2.6-6.5% at lower spiked concentrations and 3.0-4.6% at higher concentrations. Good linearity of analytes was achieved in the range of 0.5-500 µg L(-1). The acceptable relative recoveries (82.9-112.4%) for environmental waters revealed the presence of negligible matrix effects in the case of real samples. The applicability of this newly developed method was illustrated by determinations of CPAs and CPs in environmental water samples.