In-tube solid-phase microextraction-capillary liquid chromatography as a solution for the screening analysis of organophosphorus pesticides in untreated environmental water samples

This paper describes a method for the selective screening of organophosphorus pesticides in water. In-tube solid-phase microextraction (SPME) in an open capillary column coupled to capillary liquid chromatography (LC) with UV detection has been used to effect preconcentration, separation and detection of the analytes in the same assembly. For in-tube SPME two capillary columns of the same length and different internal diameters and coating thicknesses have been tested and compared, a 30 cm x 0.25 mm I.D., 0.25 micro m thickness coating column, and a 30 cm x 0.1 mm I.D., 0.1 micro m of coating thickness column. In both columns the coating was 95% dimethylpolysiloxane (PDMS)-5% diphenylpolysiloxane. The proposed methodology provided limits of detections (LODs) for the tested organophosphorus pesticides in the 0.1-10 micro g/L range, whereas the direct injection of the samples onto the capillary LC system provided LODs in the 50-1000 micro g/L range. The sensitivity of the proposed in-tube SPME-capillary LC method is adequate to monitorize the analyte levels in drinking water. Several triazines, polycyclic aromatic hydrocarbons (PAHs), nonylphenol, organochloride pesticides or polybrominated diphenyl ethers (PBDEs) have been evaluated as possible interferents. The reliability of the described method is demonstrated by analysing different real water samples.     

Analyses of non-steroidal anti-inflammatory drugs by on-line concentration capillary electrochromatography using poly(stearyl methacrylate-divinylbenzene) monolithic columns

This study describes the ability of on-line concentration capillary electrochromatography (CEC) coupled with UV or mass spectrometry (MS) for the determination of nine common non-steroidal anti-inflammatory drugs (NSAIDs) in water samples. A series of poly(stearyl methacrylate-divinylbenzene) (poly(SMA-DVB)) monolithic columns, which were prepared by single step in situ polymerization of divinylbenzene (DVB), stearyl methacrylate (SMA) and vinylbenzenesulfonic acid (VBSA, charged monomer), were developed as separation columns for the first time. The effects of polymerization condition of monolithic columns on analyte separations were examined, and the results indicated that separation performances were markedly improved in monolithic columns prepared with short reaction time (3 h) and low SMA:DVB ratio (40/60 ratio of SMA:DVB). Subsequently, an on-line concentration step of step-gradient elution was combined to this CEC system, and by optimizing the difference in eluent strength between the sample matrix and mobile phase, all NSAIDs detection sensitivity were improved (limit of detection (LOD) was 3.4-10 μg/L for UV, and 0.01-0.19 μg/L for MS). When compared to the best CE and LC reports on NSAIDs analyses so far, this on-line concentration CEC method provided better detection ability within shorter separation time (12 min) when either UV or MS detector was employed. This is the first report for on-line concentration CEC with MS detection applied in trace solute analyses of real samples.     

Temperature effects on separation on zirconia columns: applications to one- and two-dimensional LC separations of phenolic antioxidants

The effects of temperature and mobile phase on LC chromatographic separation of phenolic antioxidants on zirconia-based columns were investigated. Unlike silica-based materials, zirconia columns show excellent thermal stability over a wide range of temperatures and enable high-temperature separations. Enthalpic and entropic contributions to the retention of phenolic compounds on ZR-Carbon and ZR-Carbon C18 columns were determined from retention versus temperature plots in order to elucidate the retention mechanism of sample compounds over the temperature range up to 14 degrees C. High-temperature liquid chromatography on ZR-Carbon columns was used for comprehensive LC x LC two-dimensional separation systems based on the different selectivity of a Zorbax SB micro-column used in the first dimension and a ZR-Carbon column used in the second dimension. Two-dimensional LC x LC systems employing a setup with two alternately operated parallel ZR-Carbon columns in the second dimension were used for the analysis of phenolic antioxidants in beer and wine samples.     

Quantitative determination of DNA adducts using liquid chromatography/electrospray ionization mass spectrometry and liquid chromatography/high-resolution inductively coupled plasma mass spectrometry

The quantitative determination of nucleotides from DNA modified by styrene oxide is described using a combination of inductively coupled plasma high-resolution mass spectrometry (ICP-HRMS) and electrospray ionization mass spectrometry (ESI-MS), both interfaced to reversed-phase high-performance liquid chromatography (HPLC). LC/ICP-MS (resolution > 1500 to discriminate against 15N16O+ and 14N16OH+) was employed to determine quantitatively the content of modified nucleotides in standard solutions based on the signal of phosphorus; phosphoric acid served as an internal standard. By means of the standard addition technique the sensitivity of the LC/ESI-MS approach was subsequently determined. Since a comparison of UV, ICP and ESI-MS data suggested that in ESI-MS the ionization efficiency of the adducts is identical within the error limits, quantitative determination of all adducts is possible. For LC/ESI-MS with single ion monitoring, the detection limit for styrene oxide adducts of nucleotides was determined to be 20 pg absolute or 14 modified in 10(8) unmodified nucleotides in a 5 micrograms DNA sample, which comes close to the best methods available for the detection of chemical modifications in DNA.     

离子排斥色谱用于厌氧消化处理水中脂肪族羧酸的分析（英文）

The analysis of seven aliphatic carboxylic acids(formic,acetic,propionic,iso-butyric,n-butyric,iso-valeric and n-valeric acid) in anaerobic digestion process waters for biogas production was examined by ion-exclusion chromatography with dilute acidic eluents(benzoic acid,perfluorobutyric acid(PFBA) and sulfuric acid) and non-suppressed conductivity/ultraviolet(UV) detection.The columns used were a styrene/divinylbenzene-based strongly acidic cation-exchange resin column(TSKgel SCX) and a polymethacrylate-based weakly acidic cation-exchange resin column(TSKgel Super IC-A/C).Good separation was performed on the TSKgel SCX in shorter retention times.For the TSKgel Super IC-A/C,peak shape of the acids was sharp and symmetrical in spite of longer retention times.In addition,the mutual separation of the acids was good except for iso-and n-butyric acids.The better separation and good detection was achieved by using the two columns(TSKgel SCX and TSKgel Super IC-A/C connected in series),lower concentrations of PFBA and sulfuric acid as eluents,non-suppressed conductivity detection and UV detection at 210 nm.This analysis was applied to anaerobic digestion process waters.The chromatograms with conductivity detection were relatively simpler compared with those of UV detection.The use of two columns with different selectivities for the aliphatic carboxylic acids and the two detection modes was effective for the determination and identification of the analytes in anaerobic digestion process waters containing complex matrices.     

Identification of reaction products of methamphetamine and hydrogen peroxide in hair dye and decolorant treatments by high-performance liquid chromatography/mass spectrometry

The effect of hydrogen peroxide, a main component of hair dye and decolorant treatments, on methamphetamine (MA) was studied. Two analytical methods, thin-layer chromatography (TLC) and high-performance liquid chromatography/mass spectrometry (LC/MS), were used for the separation and identification of MA derivatives. Mixtures of MA solutions and hydrogen peroxide that had been incubated at 39 degrees C for 24 h were shown to contain para-hydroxy MA by TLC and para-, meta- and ortho-hydroxy MAs by LC/MS. In addition, MA N-oxide and N-hydroxy MA were found in MA/hydrogen peroxide mixtures immediately after mixing. Therefore, we concluded that MA changed to MA N-oxide and N-hydroxy MA before changing to para-, meta- and ortho-hydroxy MAs.     

Multidimensional LC x LC analysis of phenolic and flavone natural antioxidants with UV-electrochemical coulometric and MS detection

A comprehensive 2-D LC x LC system was developed for the separation of phenolic and flavone antioxidants, using a PEG-silica column in the first dimension and a C(18) column with porous-shell particles or a monolithic column in the second dimension. Combination of PEG and C18 or C8 stationary phase chemistries provide low selectivity correlations between the first dimension and the second dimension separation systems. This was evidenced by large differences in structural contributions to the retention by -COOH, -OH and other substituents on the basic phenol or flavone structure. Superficially porous columns with fused core particles or monolithic columns improve the resolution and speed of second dimension separation in comparison to a fully porous particle C(18) column. Increased peak capacity and high orthogonality in different 2-D setups was achieved by using gradients with matching profiles running in parallel in the two dimensions over the whole 2-D separation time range. Multi-dimensional set-up combining the LC x LC separation on-line with UV and multi-channel coulometric detection and off-line with MS/MS technique allowed positive peak identification. The Coularray software compensates for the effects of the baseline drift during the gradient elution and is compatible with parallel gradient comprehensive LC x LC technique. Furthermore, it provides significant improvement in the sensitivity and selectivity of detection in comparison to both UV and MS detection. The utility of these systems has been demonstrated in the analysis of beer samples.     

High efficiency liquid chromatography on conventional columns and instrumentation by using temperature as a variable. Kinetic plots and experimental verification

Theoretical aspects of temperature in liquid chromatography (LC) have mostly been studied to elucidate changes in retention behavior of small and large molecules in various solvents. That temperature also plays a significant role in chromatographic performance is less known. Kinetic plots are an established tool to predict chromatographic performance in terms of speed and efficiency that can be obtained with a certain particle size at the maximum attainable column pressure. In this paper, temperature effects on mobile phase viscosity and analyte diffusion are incorporated in these plots to prove that superior performances are within experimental reach for conventional LC columns and equipment. Verification of the modified kinetic plots with experimental data points is presented.     

Investigation of particle-based and monolithic columns for cation exchange protein displacement chromatography using poly(diallyl-dimethylammonium chloride) as displacer

The overall topic of the investigation was the separation of basic proteins by cation exchange displacement chromatography. For this purpose two principal column morphologies were compared for the separation of ribonuclease A and alpha-chymotrypsinogen, two proteins found in the bovine pancreas. These were a column packed with porous particles (Macro-Prep S, 10 microm, 1000 A) and a monolithic column (UNO S1). Both columns are strong cation exchangers, carrying -SO3(-)-groups linked to a hydrophilic polymer support. Poly(diallyl-dimethylammonium chloride) (PDADMAC), a linear cationic polyelectrolyte composed of 100-200 quaternary pyrrolidinium rings, was used as displacer. The steric mass action (SMA) model and, in particular, the operating regime and dynamic affinity plots were used to aid method development. To date the SMA model has been applied primarily to simulate non-linear displacement chromatography of proteins using low molar mass displacers. Here, the model is applied to polyelectrolytes with a molar mass below 20000 g mol(-1), which corresponds to a degree of polymerization below 125 and an average contour length of less than 60 nm. The columns were characterized in terms of the adsorption isotherms (affinity, capacity) of the investigated proteins and the displacer.     

Comprehensive two-dimensional liquid chromatography in analysis of Lamiaceae herbs: characterisation and quantification of antioxidant phenolic acids

A fast and effective dynamic sonication assisted ethanol extraction method was developed for extracting phenolic acids from basil, oregano, rosemary, sage, spearmint and thyme of the Lamiaceae family. The results were compared with results obtained by conventional solvent extraction techniques. A comprehensive two-dimensional liquid chromatography (LC x LC) system interfaced to electrospray ionisation time-of-flight (TOF) mass spectrometry was then optimised for analysis and quantification of the herb extracts. The optimised LC x LC system employed a combination of C18 and cyano columns. The relative standard deviations for the retention times were better than 0.05% (rosmarinic acid 0.1%) and those for the peak areas 2-14% (2 mg/l, n=3). Limits of detection were 18-90 ng/ml. The LC x LC-MS method was applied to the quantitative analysis of phenolic acids, and the results were compared with those obtained with conventional LC-MS.     

Fast HPLC with a silica-based monolithic ODS column

Fast high-performance liquid chromatography is becoming routine in laboratories that require high throughput or for combinatorial libraries. Reduced analysis time is commonly achieved by using shorter columns and higher flow rates. Shorter columns require smaller particles in order to maintain efficiency. However, smaller particles increase backpressure, which limits both column length and higher flow rates for typical LC pumps. This disadvantage has been addressed by the emergence of monolithic liquid chromatographic columns (1). Unlike particle-base columns, monolithic columns consist of a continuous rod-shaped porous network with a bimodal pore distribution. In this study, a commercially available 50- x 4.6-mm silica-based octadecyl silane monolithic column (Chromolith SpeedROD RP18e, EM Science, Gibbstown, NJ) was used to separate a seven-component test mixture with a wide range of polarity. The primary goals of this investigation were: (a) to study the chemistry (selectivity) of the new silica-based monolithic columns and (b) to study their run-to-run and column-to-column performance (retention times and peak areas). The selectivity (alpha factor) is a ratio of partition coefficients and, if comparable for a variety of solutes, would mean that methods could be readily transferred between particulate and monolithic columns.     

Multiresidue determination of quinolones regulated by the European Union in bovine and porcine plasma. Application of chromatographic and capillary electrophoretic methodologies

This paper presents the multiresidue determination of the series of quinolones regulated by the European Union (marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, oxolinic acid and flumequine) in bovine and porcine plasma using capillary electrophoresis and liquid chromatography with ultraviolet detection (CE‐UV, LC‐UV), liquid chromatography–mass spectrometry and –tandem mass spectrometry (LC‐MS, LC‐MS/MS) methods. These procedures involve a sample preparation by solid‐phase extraction for clean‐up and preconcentration of the analytes before their injection into the separation system. All methods give satisfactory results in terms of linearity, precision, accuracy and limits of quantification. The suitability of the methods to determine quinolones was evaluated by determining the concentration of enrofloxacin and ciprofloxacin in real samples from pig plasma and cow plasma. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimization of a liquid chromatography method based on simultaneous electrospray ionization mass spectrometric and ultraviolet photodiode array detection for analysis of flavonoid glycosides

Different reversed-phase liquid chromatography (LC) columns of conventional dimensions were coupled to an ultraviolet photodiode array detector (UV-DAD) and a magnetic sector-type spectrometer, equipped with an electrospray ionization (ESI) source, by a laboratory-made flow splitter. A mixture of three flavonoid-O-glycosides was employed to examine the effects of the solvent composition, the flow rate, the stationary phase, the pH and the organic acid added, on the chromatographic separation, the UV-DAD detection, the ESI process and the entire LC system with ESI-MS and UV-DAD detection. In the positive ion mode, methanol containing 1% acetic acid was by far the most sensitive in ESI-MS analysis, whereas an acetonitrile/water mobile phase containing 0.5% formic acid was proved to give the best sensitivity in LC/ESI-MS/UV-DAD analysis. In the negative ion mode, the highest sensitivity was obtained with a mobile phase containing 0.1% formic acid, while addition of bases decreased the sensititvity. The optimal flow rate was higher in negative ESI (20-50 micro L/min) than in positive ESI (5 micro L/min), and the percentage of organic phase had an influence on the sensitivity of ESI-MS detection. With regard to the selection of a suitable C(18) reversed-phase LC column, a column which is well end-capped is to be preferred, because residual silanol groups appear to impair the separation of flavonoid glycosides. The optimized LC/ESI-MS/UV-DAD method was applied to a commercial Crataegus extract, which is used in phytomedicine to treat cardiovascular problems and is known to be rich in flavonoids. It is demonstrated how UV spectra and first-order ESI mass spectra allow a fast characterization of flavonoids, even if reference compounds are not available or at hand.     

Coupling of Ultrafast LC with Mass Spectrometry by DESI

Recently we reported a desorption electrospray ionization (DESI) interface to combine liquid chromatography (LC) with mass spectrometry (MS) using a new LC eluent splitting strategy through a tiny orifice on LC capillary tube [J. Am. Soc. Mass Spectrom. 25, 286 (2014)]. The interface introduces negligible dead volume and back pressure, thereby allowing “near real-time” MS detection, fast LC elution, and online MS-directed purification. This study further evaluates the LC/DESI-MS performance with focus of using ultra-fast LC. Using a monolithic C₁₈ column, metabolites in urine can be separated within 1.6 min and can be online collected for subsequent structure elucidation (e.g., by NMR, UV, IR) in a recovery yield up to 99%. Using a spray solvent with alkaline pH, negative ions could be directly generated for acidic analytes (e.g., ibuprofen) in acidic LC eluent by DESI, offering a novel protocol to realize “wrong-way around” ionization for LC/MS analysis. In addition, DESI-MS is found to be compatible with ultra-performance liquid chromatography (UPLC) for the first time.      

Hyphenation of infrared spectroscopy to liquid chromatography for qualitative and quantitative polymer analysis: degradation of poly(bisphenol A)carbonate

Hyphenation of infrared spectroscopy (IR) to liquid chromatography (LC) has been applied to study chemical changes in poly(bisphenol A)carbonate (PC) as a result of degradation. Especially coupling of LC to FTIR through solvent elimination is a sensitive approach to identify changes in functionality observed in the LC chromatograms as has been demonstrated by coupling of liquid chromatography under critical conditions (LCCC) to IR. Furthermore, an example is shown in which two-dimensional liquid chromatography, i.e. LCCCxSEC, was coupled to IR by means of a flow cell. This resulted in data sets containing most probably valuable data, but extracting relevant information from these large data sets is not straightforward at all. Therefore, multivariate data analysis (MVDA) of SEC-FTIR data was used to extract relevant data from large data sets. This approach revealed chemical differences due to degradation that could not be detected by other means. Spectral features could be identified that allowed to quantitatively predict the degradation of poly(bisphenol A)carbonate as a function of degradation conditions.     

Toxicological screening by liquid chromatography

Toxicological screening commonly requires analysis of biological specimens by a variety of colorimetric, immunological and chromatographic techniques. Gas chromatography and thin-layer chromatography are useful for simultaneous identification of multiple drug classes, but both methods require sample pretreatment. Recently, liquid chromatography has been applied to untreated urine and serum. A series of columns are utilized for sample purification, as well as efficient separation of drugs. Multiple wavelength UV detection provides sufficient data for qualitative identification of drugs and their metabolites.     

Development and optimization of a system for comprehensive two-dimensional liquid chromatography with UV and mass spectrometric detection for the separation of complex samples by multi-step gradient elution

Comprehensive two-dimensional liquid chromatography (LC x LC) is a powerful tool for the separation of complex biological samples. This technique offers the advantage of simplified automation and greater reproducibility in a shorter analysis time than off-line two-dimensional separation systems. In the present study, an LC x LC system is developed enabling simultaneous UV and MS detection, and which can be easily converted to a conventional reversed-phase LC-UV/MS system. In LC x LC, a 60-min reversed-phase LC separation with a linear solvent gradient in the first dimension is coupled to a second-dimension separation on a mixed-mode cation-exchange/reversed-phase column with a modulation time of 60s. The isocratic separation in the second-dimension column is optimized by the use of a multi-step gradient where the organic and the ionic modifier are varied independently. Intraday (n=3) and interday (n=4) variability of the retention times were evaluated with the complete system and found to be 0.5% and 0.7%, respectively. Good linearity was observed in calibration curves for three different compounds varying in polarity.     

Microcolumn liquid chromatography of the enantiomers of organophosphorus pesticides with thermionic and ultraviolet detection

Microcolumn liquid chromatography (micro-LC) of some chiral organophosphorus pesticides has been studied using Chiralcel OD columns and simultaneous ultraviolet (UV) and phosphorus selective detection, the latter by means of a micro-UV cell coupled on-line to a thermionic detector (TID). Micro-LC showed a ca. 5-fold improved separation impedance, a ca. 1.8-fold increased column permeability, and greater inertness compared with conventional LC. By using the TID, organophosphorus pesticides could be satisfactorily determined at trace levels, the detection limit being 4 pg/s of phosphorus. The response of the micro-LC-TID system is linear in the range of 0.05–20 ng (r = 0.9994).     

A novel approach for sensitivity enhancement in atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry of chlorophylls

Differences in the ionisation efficiency of chlorophylls and their phaeophytin counterparts result in lower sensitivity for atmospheric pressure chemical ionisation mass spectrometric detection of the former. Improvement in the sensitivity of detection of chlorophyll of around an order of magnitude at a concentration of 1 x 10(-6)mol L(-1) has been achieved using post-column addition of methanoic acid during analysis by liquid chromatography/mass spectrometry (LC/MS). The method gives linear response and is a simple strategy to improve sensitivity both for LC/MS and LC/MS/MS without loss of information relating to the precise nature of the tetrapyrrole distributions. Detection levels achieved exceed those obtained by absorbance detection.