High-performance Liquid Chromatography System Research Articles

Factors that Restrict the Cell Permeation of Cyclic Prodrugs of an Opioid Peptide, Part 3: Synthesis of Analogs Designed to have Improved Stability to Oxidative Metabolism

Previously, our laboratory reported that cyclic peptide prodrugs of the opioid peptide H-Tyr-D-Ala-Gly-Phe-D-Leu-OH (DADLE) are metabolized by cytochrome P450 (CYP450) enzymes, which limits their systemic exposure after oral dosing to animals. In an attempt to design more metabolically stable cyclic prodrugs of DADLE, we synthesized analogs of DADLE cyclized with a coumarinic acid linker (CA; CA-DADLE), which contained modifications in the amino acid residues known to be susceptible to CYP450 oxidation. Metabolic stability and metabolite identification studies of CA-DADLE and its analogs were then compared using rat liver microsomes (RLM), guinea pig liver microsomes (GPLM), and human liver microsomes (HLM), as well as recombinant human recombinant cytochrome P450 3A4 (hCYP3A4). Similar to the results observed for CA-DADLE, incubation of its analogs with RLM, GPLM, and HLM resulted in monohydroxylation of an amino acid side chain on these cyclic prodrugs. When CA-DADLE was incubated with hCYP3A4, similar oxidative metabolism of the peptide was observed. In contrast, incubation of the CA-DADLE analogs with hCYP3A4 showed that these amino-acid-modified analogs are not substrates for this CYP450 isozyme. These results suggest that the amino-acid-modified analogs of CA-DADLE prepared in this study could be stable to metabolic oxidation by CYP3A4 expressed in human intestinal mucosal cells.

Identification of Geometrical Isomers and Comparison of Different Isomeric Samples of Astaxanthin

A high-performance liquid chromatographic (HPLC) analysis system for isomeric astaxanthin was developed. The separation system consisted of a C(30) column and an elution system of methanol/MTBE/water/dichloromethane (77:13:8:2, v/v/v/v). Using the combination of HPLC diode array detector and HPLC atmospheric pressure chemical ionization mass spectrometry, 11 geometrical isomers and 4 epoxides of astaxanthin were successfully identified. Referred to crystal, only isomerization with different degrees was found for solvent dissolving and iodine catalysis, while melting of astaxanthin caused isomerization, slight oxidation, and more noticeable polymerization confirmed by gel permeation chromatography. Chemical changes in isomeric samples all caused a decrease in UV content. The vibrational spectra (infrared and Raman) showed that epoxide was the only new functional group generated for melting. Changes of several key bands and formations of new bands were found in iodine catalysis and melting samples because of isomerization. Practical Application: Eleven geometrical isomers and 4 epoxides, which were normally generated for solvent dissolving, iodine catalysis, and melting of astaxanthin, have been identified by C(30) -HPLC-MS technology. Furthermore, different samples were measured by gel permeation chromatography, UV, infrared, and Raman, based on the analysis of messages, the effect of each processing was well understood.

Characterization, concentrations and emission rates of polycyclic aromatic hydrocarbons in the exhaust emissions from in-service vehicles in Damascus

Motor vehicles are significant sources of polycyclic aromatic hydrocarbon (PAH) emissions to the urban atmosphere. Improved understanding of PAH emission profiles in mobile sources is the key to determining the viable approach for reducing PAH emissions from motor vehicles. Very limited data is available on the levels of PAH emissions in the urban atmospheres in Syria and no data are currently available on the level of PAH emissions from different combustion sources in the country. The aim of this study was to determine the profile and concentration of PAH in exhaust emissions of light and heavy-duty vehicles running on the roads of Damascus city. Three different types of vehicles (passenger cars, minivans and buses) were selected along with different age groups. Vapor- and particulate-phase PAH were collected from the vehicular exhausts of six in-service vehicles (with/without catalytic converters). High-performance liquid chromatography system, equipped with UV–Visible and fluorescence detectors, was used for the identification and quantification of PAH compounds in the cleaned extracts of the collected samples. The mean concentration of total PAH emissions (sum of 15 compounds) from all types of studied vehicles ranged between 69.28±1.06μg/m3 for passenger cars equipped with catalytic converters and 2169.41±5.17μg/m3 for old diesel buses without pollution controls. Values of total benzo(a)pyrene equivalent (∑B[a]Peq) ranged between 1.868μg/m3and 37.652μg/m3. The results obtained in this study showed that the use of catalytic converters resulted into cleaner exhaust compositions and emissions with characteristics that are distinct from those obtained in the absence of catalytic converters.

A simple solvent collection technique for a dispersive liquid–liquid microextraction of parabens from aqueous samples using low‐density organic solvent

A simple technique for the collection of an extraction solvent lighter than water after dispersive liquid-liquid microextraction combined with high-performance liquid chromatography with ultraviolet detection was developed for the determination of four paraben preservatives in aqueous samples. After the extraction procedure, low-density organic solvent together with some little aqueous phase was separated by using a disposable glass Pasteur pipette. Next, the flow of the aqueous phase was stopped by successive dipping the capillary tip of the pipette into anhydrous Na(2)SO(4). The upper organic layer was then removed simply with a microsyringe and injected into the high-performance liquid chromatography system. Experimental parameters that affect the extraction efficiency were investigated and optimized. Under optimal extraction conditions, the extraction recoveries ranged from 25 to 86%. Good linearity with coefficients with the square of correlation coefficients ranging from 0.9984 to 0.9998 was observed in the concentration range of 0.001-0.5 μg/mL. The relative standard deviations ranged from 4.1 to 9.3% (n = 5) for all compounds. The limits of detection ranged from 0.021 to 0.046 ng/mL. The method was successfully applied for the determination of parabens in tap water and fruit juice samples and good recoveries (61-108%) were achieved for spiked samples.

Apertured impedance microchips: Surface modification and evaluation using high performance liquid chromatography

Abstract The present study evaluates the performance and potential utility of apertured impedance microchips (AIMs). The electronics-based, dielectric constant detection devices feature a novel layered architecture with aluminum metal/silicon-oxide/silicon layers, where the top metal layer has apertures and the middle oxide layer has wells. This layered yet open geometry enables molecules to have access to detection of electric fields induced by a voltage applied between the top metal/bottom silicon electrode layers. Our design rationale surmised that the AIM device's large footprint area and thin nanoscale oxide layer should enable impedance detection of molecules with high sensitivity in a variety of solvents. The present study confirms this hypothesis and explores the effects that simple surface modifications have on the device's response. Specifically, the affinity between various analytes and the device's surface is evaluated when: (a) the aluminum top electrode is hydrated and rendered hydrophilic by immersing the microchip in boiling water, and (b) the silicon substrate is stripped of oxide and rendered hydrophobic (hydrogen-terminated) by hydrofluoric acid (HF) wet etching. Both types of devices were incorporated into a high performance liquid chromatography (HPLC) system already equipped with an ultra-violet–visible (UV–vis) detector. A range of analytes was injected using both normal and reverse phase modes; and the signals generated by each microchip device and UV–vis detector were recorded simultaneously and compared. The microchip devices’ responses were found to vary for analytes according to the surface modification used. The second surface modification method of exposing bare silicon surface showed greater sensitivity than the first method for all the analytes. Both types of devices were remarkably sensitive to organic salts tested, i.e., their sensitivity was significantly greater than that of the UV–vis detector. To demonstrate the novel dielectric constant capability of AIM, as a case study, the HF-treated device was used to detect enantiomers of a synthesized chiral molecule separated by a chiral column using an insulating eluent, namely hexanes/isopropanol.

Development of a two-dimensional high-performance liquid chromatography system coupled with on-line reduction as a new efficient analytical method of 3-nitrobenzanthrone, a potential human carcinogen

3-Nitrobenzanthrone (3-NBA) is an extremely strong mutagen and carcinogen in rats inducing squamous cell carcinoma and adenocarcinoma. We developed a new sensitive analytical method, a two-dimensional HPLC system coupled with on-line reduction, to quantify non-fluorescent 3-NBA as fluorescent 3-aminobenzanthrone (3-ABA). The two-dimensional HPLC system consisted of reversed-phase HPLC and normal-phase HPLC, which were connected with a switch valve. 3-NBA was purified by reversed-phase HPLC and reduced to 3-ABA with a catalyst column, packed with alumina coated with platinum, in ethanol. An alcoholic solvent is necessary for reduction of 3-NBA, but 3-ABA is not fluorescent in the alcoholic solvent. Therefore, 3-ABA was separated from alcohol and impurities by normal-phase HPLC and detected with a fluorescence detector. Extracts from surface soil, airborne particles, classified airborne particles, and incinerator dust were applied to the two-dimensional HPLC system after clean-up with a silica gel column. 3-NBA, detected as 3-ABA, in the extracts was found as a single peak on the chromatograms without any interfering peaks. 3-NBA was detected in 4 incinerator dust samples (n=5). When classified airborne particles, that is, those <1.1, 1.1–2.0, 2.0–3.3, 3.3–7.0, and >7.0μm in size, were applied to the two-dimensional HPLC system after purified using a silica gel column, 3-NBA was detected in those particles with particle sizes <1.1 and 1.1–2.0μm and the particle-size distribution ratios were 84% and 16%, respectively. This is the first report on the particle-size distribution of 3-NBA in airborne particles and the detection of 3-NBA in incinerator dust.

Pesticide Residues in Tobacco Leaves from the Kushtia District in Bangladesh

In this study, tobacco leaf samples (n=26) were collected from different areas in Kushtia to determine the presence of residues of cypermethrin, diazinon, heptachlor, methoxychlor dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethan (DDD) and dichlorodiphenyldichloroethylene (DDE). The analysis was conducted by a High Performance Liquid Chromatography (HPLC) system that was equipped with a photodiode array detector. Both cypermethrin and diazinon were detected in tobacco samples from six districts, namely, Mirzapur, Shahebnagar, Kodalipara, Pragpur, Farakpur and Taragunia. The highest concentration of cypermethrin was found in Kodalipara (2.00ppm) while the highest concentration of diazinon was detected in a sample from Pragpur (0.15ppm). The pesticide DDT was only detected in the sample from Pragpur at 4.00ppm. This is the first study in Bangladesh that reports pesticide residue concentrations in tobacco leaf samples.

Sample handling and contamination encountered when coupling offline normal phase high performance liquid chromatography fraction collection of petroleum samples to Fourier transform ion cyclotron resonance mass spectrometry

Normal phase high performance liquid chromatography (HPLC) is used to separate a gas oil petroleum sample, and the fractions are collected offline and analyzed on a high resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS). The separation prior to MS analysis dilutes the sample significantly; therefore the fractions need to be prepared properly to achieve the best signal possible. The methods used to prepare the HPLC fractions for MS analysis are described, with emphasis placed on increasing the concentration of analyte species. The dilution effect also means that contamination in the MS spectra needs to be minimized. The contamination from molecular sieves, plastics, soap, etc. and interferences encountered during the offline fraction collection process are described and eliminated. A previously unreported MS contamination of iron formate clusters with a 0.8 mass defect in positive mode electrospray is also described. This interference resulted from the stainless steel tubing in the HPLC system. Contamination resulting from what has tentatively been assigned as palmitoylglycerol and stearoylglycerol was also observed; these compounds have not previously been reported as contaminant peaks.

In-situ metathesis reaction combined with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction method for the determination of phenylurea pesticides in water samples

A novel microextraction technique, named in-situ metathesis reaction, combined with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction was developed for the determination of five phenylurea pesticides (i.e., diuron, diflubenzuron, teflubenzuron, flufenoxuron, and chlorfluazuron) in environmental water samples. In the developed method, 360μL LiNTf2 aqueous solution (0.162g/mL) was added to the sample solution containing a small amount of [C6MIM]Cl (0.034g) to form a water-immiscible ionic liquid, [C6MIM]NTf2, as extraction solution. The mixed solutions were placed in an ultrasonic water bath at 150W for 4min and centrifuged at 3500rpm for 10min to achieve phase separation. After centrifugation, fine droplets of the extractant phase settled to the bottom of the centrifuge tube and were directly injected into the high-performance liquid chromatography system for analysis. The quantity of [C6MIM]Cl, the molar ratio of [C6MIM]Cl and LiNTf2, ionic strength, ultrasound time, and centrifugation time, were optimized using a Plackett–Burman design. Significant factors obtained were optimized by employing a central composite design. The optimized technique provides good repeatability (RSD 2.4 to 3.5%), linearity (0.5μg/L to 500μg/L), low LODs (0.06μg/L to 0.08μg/L) and great enrichment factor (244 to 268). The developed method can be applied in routine analysis for the determining of phenylurea pesticides in environmental samples.

Performance of chromatographic systems to model soil–water sorption

A systematic approach for evaluating the goodness of chromatographic systems to model the sorption of neutral organic compounds by soil from water is presented in this work. It is based on the examination of the three sources of error that determine the overall variance obtained when soil–water partition coefficients are correlated against chromatographic retention factors: the variance of the soil–water sorption data, the variance of the chromatographic data, and the variance attributed to the dissimilarity between the two systems. These contributions of variance are easily predicted through the characterization of the systems by the solvation parameter model. According to this method, several chromatographic systems besides the reference octanol–water partition system have been selected to test their performance in the emulation of soil–water sorption. The results from the experimental correlations agree with the predicted variances. The high-performance liquid chromatography system based on an immobilized artificial membrane and the micellar electrokinetic chromatography systems of sodium dodecylsulfate and sodium taurocholate provide the most precise correlation models. They have shown to predict well soil–water sorption coefficients of several tested herbicides. Octanol–water partitions and high-performance liquid chromatography measurements using C18 columns are less suited for the estimation of soil–water partition coefficients.

Influence of temperature on peak shape and solvent compatibility: Implications for two‐dimensional liquid chromatography

Solvent compatibility is a limiting factor for the success of two-dimensional liquid chromatography (2-D LC). In the second dimension, solvent effects can result in overpressures as well as in peak broadening or even distortion. A peak shape study was performed on a one-dimensional high-performance liquid chromatography (HPLC) system to simulate the impact of peak distorting solvent effects on a reversed-phase second dimension separation operated at high temperatures. This study includes changes in injection volume, solute concentration, column inner diameter, eluent composition and oven temperature. Special attention was given to the influence of high temperatures on the solvent effects. High-temperature HPLC (HT-HPLC) is known to enhance second dimension separations in terms of speed, selectivity and solvent compatibility. The ability to minimise the viscosity contrast between the mobile phases of both dimensions makes HT-HPLC a promising tool to avoid viscosity mismatch effects like (pre-)viscous fingering. In case of our study, viscosity mismatch effects could not be observed. However, our results clearly show that the enhancement in solvent compatibility provided by the application of high temperatures does not include the elimination of solvent strength effects. The additional peak broadening and distortion caused by this effect is a potential error source for data processing in 2-D LC.

A Fast HPLC Method for Determination of Vitamin E Acetate in Dietary Supplements Using Monolithic Column

A simple and fast high-performance liquid chromatography (HPLC) method with rapid separation on monolithic column has been developed for quantitative determination of vitamin E acetate in dietary supplements. Commercial samples of dietary supplements were extracted with 100 % methanol with the help of ultrasound bath. A 20-μL sample volume of the filtered solution was directly injected into the HPLC system. Separation of ballast matrix, vitamin E acetate, and internal standard cholecalciferol was performed on the monolithic column Chromolith Performance RP-18e column (100 × 4.6 mm) with mobile phase methanol/water (98:2, v/v) at a flow rate of 2.0 mL min−1 and at temperature 30 °C. The detector was set at 290 nm. Under the optimum chromatographic conditions, standard calibration curve was measured with good linearity—correlation coefficient for vitamin E acetate (r = 0.9992; n = 6) between the peak areas and concentrations of vitamin E acetate. Accuracy of the method defined as a mean recovery was in the range 96.4–103.6 % for all dietary supplements. The intraday method precision was satisfactory and relative standard deviation of sample analysis including preparation and determination of different dietary supplements was in the range 1.1–3.6 %. The developed method has shown high sample throughput during sample preparation process and short time (3.5 min) of analysis.

Combined Therapy With Thioridazine Decreases Plasma Levels of Quetiapine in Taiwanese Schizophrenic Patients

In this study, the authors studied the effect of thioridazine (TDZ) on the pharmacokinetic profile of quetiapine (QTP) in Taiwanese patients with schizophrenia. Sixteen subjects with schizophrenia were recruited for this study. The authors pretreated 8 patients with TDZ 50 mg daily continuously given until the end of the study. QTP was administered to all the participants, and their doses were escalated to 300 mg once daily over a 7-day period and maintained for another week. On day 15, blood samples were collected at 12 time points within an 8-hour interval. The authors assayed the plasma levels of QTP with a high-performance liquid chromatography system coupled with ultraviolet detector. Significantly decreased plasma levels of QTP after oral administration were observed in patients comedicated with TDZ compared with the QTP monotherapy group at 1.5, 2, and 2.5 hours, and the P values were 0.046, 0.001, and 0.005, respectively. The Cmax of QTP was significantly lower in the group comedicated with TDZ (776.9 ± 175.2 versus 1452.3 ± 707.5 ng/mL; P = 0.002). The oral clearance of QTP was significantly higher in the combined group than in the monothreapy group (123.3 ± 66.8 versus 60.3 ± 28.5 L/h; P = 0.03). Other pharmacokinetic parameters were not significantly different. The coadministration of TDZ significantly decreased plasma QTP level and significantly increased the oral clearance of QTP. Although TDZ is switched to QTP, choosing larger doses of QTP for titration may be necessary to avoid the emergence of psychotic symptoms among schizophrenic patients.

A Proteomic Approach To Investigate the Distribution and Abundance of Surface and InternalFasciola hepaticaProteins during the Chronic Stage of Natural Liver Fluke Infection in Cattle

Fasciola hepatica, a trematode helminth, causes an economically important disease (fasciolosis) in ruminants worldwide. Proteomic analysis of the parasite provides valuable information to understand the relationship between the parasite and its host. Previous studies have identified various parasite proteins, some of which are considered as vaccine candidates or important drug targets. However, the approximate distribution and abundance of the proteins on the surface and within internal parts of the liver fluke are unknown. In this study, two fractions including surface protein fraction (representing surface part of the parasite, near subplasma membrane of the tegument and above the basal membrane of the tegument) and internal protein fraction (representing internal part of the parasite, mainly deeper sides of the tegument including subbasal membrane and other further internal elements of the parasite) were obtained. Components of these two fractions were investigated by an advanced proteomics approach using a high-definition mass spectrometer with nano electrospray ionization source coupled to a high-performance liquid chromatography system (nanoUPLC-ESI-qTOF-MS). FABP1 was found highly abundant in the SPF fraction. Potentially novel F. hepatica proteins showing homology with AKT interacting protein (Xenopus tropicalis), sterol O-acyltransferase 2 (Homo sapiens), and integrin beta 7 (Mus musculus) were identified with high quantities in only the surface fraction of the parasite and may be possible candidates for future control strategies.

Selective extraction and determination of vitamin B12 in urine by ionic liquid-based aqueous two-phase system prior to high-performance liquid chromatography

A rapid and simple extraction technique based on aqueous two-phase system (ATPS) was developed for separation and enrichment of vitamin B12 in urine samples. The proposed ATPS-based method involves the application of the hydrophilic ionic liquid (IL) 1-hexyl-3-methylimidazolium chloride and K2HPO4. After the extraction procedure, the vitamin B12-enriched IL upper phase was directly injected into the high performance liquid chromatography (HPLC) system for analysis. All variables influencing the IL-based ATPS approach (e.g., the composition of ATPS, pH and temperature values) were evaluated. The average extraction efficiency was 97% under optimum conditions. Only 5.0mL of sample and a single hydrolysis/deproteinization/extraction step were required, followed by direct injection of the IL-rich upper phase into HPLC system for vitamin B12 determination. A detection limit of 0.09μgmL−1, a relative standard deviation (RSD) of 4.50% (n=10) and a linear range of 0.40–8.00μgmL−1 were obtained. The proposed green analytical procedure was satisfactorily applied to the analysis of samples with highly complex matrices, such as urine. Finally, the IL-ATPS technique could be considered as an efficient tool for the water-soluble vitamin B12 extraction.

Simultaneous quantification of metronidazole, tinidazole, ornidazole and morinidazole in human saliva

The aim of this study was to develop a rapid and sensitive method for the simultaneous quantification of metronidazole (MEZ), tinidazole (TNZ), ornidazole (ONZ) and morinidazole (MNZ) in human saliva. A reversed-phase high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detection at 318nm was carried out on a C18 column, using a mixture of potassium dihydrogen phosphate buffer, acetonitrile, and methanol (55:15:30, v/v/v) as a mobile phase with a flow rate of 1.0ml/min. The saliva samples (100μl) were firstly deproteinized by precipitation with methanol (400μl), after which they were centrifuged and the supernatants were directly injected into the HPLC system. This method produced linear responses in the concentration ranges of 25.2–5040.0, 23.9–4790.0, 25.4–5080.0, 25.0–5000.0ng/ml with detection limits of 6.0, 17.6, 10.0 and 11.3ng/ml for MEZ, TNZ, ONZ and MNZ (S/N=3), respectively. The methods were validated in terms of intra- and inter-batch precision (within 7.3% and 9.1%, respectively), accuracy, linearity, recovery and stability. The study proved that HPLC is both sensitive and selective for the simultaneous quantification of MEZ, TNZ, ONZ and MNZ in human saliva using a single mobile phase.

Mechanism of radiation-induced reactions in aqueous solution of coumarin-3-carboxylic acid: Effects of concentration, gas and additive on fluorescent product yield

The radiation-induced reactions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated in aqueous solutions by pulse radiolysis with a 35 MeV electron beam, final product analysis following 60Co γ-irradiations and deterministic model simulations. Pulse radiolysis revealed that C3CA reacted with both hydroxyl radicals (•OH) and hydrated electrons (e− aq) with near diffusion-controlled rate constants of 6.8 × 109 and 2.1 × 1010 M−1 s−1, respectively. The reactivity of C3CA towards O2• − was not confirmed by pulse radiolysis. Production of the fluorescent molecule, 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), was confirmed by final product analysis with a fluorescence spectrometer coupled to a high performance liquid chromatography (HPLC) system. Production yields of 7OH-C3CA following 60Co γ-irradiations depended on the irradiation conditions and ranged from 0.025 to 0.18 (100 eV) −1. Yield varied with saturating gas, additive and C3CA concentration, implying the presence of at least two pathways capable of providing 7OH-C3CA as a stable product following the scavenging reaction of C3CA with •OH, including a peroxidation/elimination sequence and a disproportionation pathway. A reaction mechanism for the two pathways was proposed and incorporated into a deterministic simulation, showing that the mechanism can explain experimentally measured 7OH-C3CA yields with a constant conversion factor of 4.7% from •OH scavenging to 7OH-C3CA production, unless t-BuOH was added.

Comparison of standard- and nano-flow liquid chromatography platforms for MRM-based quantitation of putative plasma biomarker proteins

The analytical performance of a standard-flow ultra-high-performance liquid chromatography (UHPLC) and a nano-flow high-performance liquid chromatography (HPLC) system, interfaced to the same state-of-the-art triple-quadrupole mass spectrometer, were compared for the multiple reaction monitoring (MRM)-mass spectrometry (MS)-based quantitation of a panel of 48 high-to-moderate-abundance cardiovascular disease-related plasma proteins. After optimization of the MRM transitions for sensitivity and testing for chemical interference, the optimum sensitivity, loading capacity, gradient, and retention-time reproducibilities were determined. We previously demonstrated the increased robustness of the standard-flow platform, but we expected that the standard-flow platform would have an overall lower sensitivity. This study was designed to determine if this decreased sensitivity could be compensated for by increased sample loading. Significantly fewer interferences with the MRM transitions were found for the standard-flow platform than for the nano-flow platform (2 out of 103 transitions compared with 42 out of 103 transitions, respectively), which demonstrates the importance of interference-testing when nano-flow systems are used. Using only interference-free transitions, 36 replicate LC/MRM-MS analyses resulted in equal signal reproducibilities between the two platforms (9.3 % coefficient of variation (CV) for 88 peptide targets), with superior retention-time precision for the standard-flow platform (0.13 vs. 6.1 % CV). Surprisingly, for 41 of the 81 proteotypic peptides in the final assay, the standard-flow platform was more sensitive while for 9 of 81 the nano-flow platform was more sensitive. For these 81 peptides, there was a good correlation between the two sets of results (R(2) = 0.98, slope = 0.97). Overall, the standard-flow platform had superior performance metrics for most peptides, and is a good choice if sufficient sample is available.

Elevated lactate dehydrogenase activity and increased cardiovascular mortality in the arsenic-endemic areas of southwestern Taiwan

Arsenic ingestion has been linked to increasing global prevalence of and mortality from cardiovascular disease (CVD); arsenic can be removed from drinking water to reduce related health effects. Lactate dehydrogenase (LDH) is used for the evaluation of acute arsenic toxicity in vivo and in vitro, but it is not validated for the evaluation of long-term, chronic arsenic exposure. The present study examined the long-term effect of chronic arsenic exposure on CVD and serum LDH levels, after consideration of arsenic metabolism capacity. A total of 380 subjects from an arseniasis-endemic area and 303 from a non-endemic area of southwestern Taiwan were recruited in 2002. Various urinary arsenic species were analyzed using high-performance liquid chromatography (HPLC) and hydride generation systems. Fasting serum was used for quantitative determination of the total LDH activity. A significant dose–response relationship was observed between arsenic exposure and LDH elevation, independent of urinary arsenic profiles (P<0.001). Furthermore, abnormal LDH elevation was associated with CVD mortality after adjustment for Framingham risk scores for 10-year CVD and arsenic exposure (hazard ratio, 3.98; 95% confidence interval, 1.07–14.81). LDH was elevated in subjects with arsenic exposure in a dose-dependent manner. LDH is a marker of arsenic toxicity associated with CVD mortality. Results of this study have important implications for use in ascertaining long-term arsenic exposure risk of CVD.

Identification of isomers and determination of octenylsuccinate in modified starch by HPLC and mass spectrometry

A high performance liquid chromatographic (HPLC) analysis of octenylsuccinic anhydride (OSA) reagent and its bound and un-reacted forms in modified starch was developed. The HPLC system consisted of a C(18) column, an elution system of acetonitrile and water containing 0.1% TFA (45:55, v/v), and a diode array detector (DAD). Using the combination of HPLC-DAD and HPLC-APCI (atmospheric pressure chemical ionisation)-MS (mass spectrometry), four main and two minor peaks were identified as 1-OS acid, cis-2-OS acid, trans-2-OS acid, 1-OSA, cis-2-OSA and trans-2-OSA, respectively. Both free and bound OS content in modified starch were successfully determined by HPLC, and direct measurement of composition of OS was achieved.