Automated on-line two-dimensional high-performance liquid chromatography method (2D-HPLC) is proposed to determine Ochratoxin A (OTA) in food samples as an alternative to OTA immunoaffinity column (IAC). An on-line 2D-HPLC system is designed for the analysis of OTA using an affinity-based monolithic column in the first dimension and reversed-phase C18 column in the second dimension. Initially, optimal OTA separation efficiency is determined through traditional HPLC system consisting of a P(HEMAPA) monolithic column coupled with HPLC system. Secondly, after providing optimum conditions, OTA determination was investigated through the 2D-HPLC system. According to results, 2D-HPLC system showed good linearity in the range 0.5 to 20 ng/mL with limit of detection (LOD) and limit of quantification (LOQ) values of 21.2 pg/mL and 64.3 pg/mL, respectively. The P(HEMAPA)-4 monolithic column displayed good recovery of OTA ranging from 104.34% to 107.33%. Relative standard deviations (RSD) varied in the range 0.21% to 1.31% thus indicating the efficiency of P(HEMAPA)-4 monolithic column developed for OTA. (C) 2018 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2018.07.057
Sayi :1569 Sayfa :139-148
A new strong cation exchanger (SCX) monolithic column was synthesized by at-line surface modification of a cryogel prepared by copolymerization of 2-hydroxyethylmethacrylate (HEMA) and glycidyl-methacrylate (GMA). Sodium salt of 3-Mercaptopropane sulfonic acid (3-MPS) was used as the ligand to transform the surface of the monolith into a strong cation exchanger. The obtained material was characterized in terms of elemental analysis, infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET) N-2 adsorption, and used as a stationary phase for strong-cation exchange chromatography of some proteins, such as a-chymotrypsinogen, cytochrome c and lysozyme. Water permeability of the column was calculated according to Darcy's law (2.66 x 10(-13) m(2)). The performance of the monolithic cryogel column was evaluated on the basis of Height Equivalent to a Theoretical Plate (HETP). Retention behavior of the studied proteins was modeled on the basis of Yamamoto model to understand the role of the ion-exchange mechanism in retention behaviors. The considered proteins were successfully separated, and the obtained chromatogram was compared with that obtained with a non-functionalized cryogel column. (c) 2015 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2015.01.075
Sayi :1386 Sayfa :13-21
This study is concerned with the incorporation of surface modified fumed silica nanoparticles (FSNPs) into polymethacrylate based monolithic columns for use in reversed phase chromatography (RPC) of small solutes and proteins. First, FSNPs were modified with 3-(trimethoxysilyl)propylmethacrylate (TMSPM) to yield the "hybrid" methacryloyl fumed silica nanoparticle (MFSNP) monomer. The resulting MFSNP was then mixed with glyceryl monomethacrylate (GMM) and ethylene dimethacrylate (EDMA) in a binary porogenic solvent composed of cyclohexanol and dodecanol, and the in situ copolymerization of MFSNP, GMM and EDMA was performed in a stainless steel column of 4.6 mm i.d. The silanol groups of the hybrid monolith thus obtained were grafted with octadecyl ligands by perfusing the hybrid monolithic column with a solution of 4% w/v of dimethyloctadecylchlorosilane (DODCS) in toluene while the column was maintained at 110 degrees C for 6 h (in a heated HPLC oven). One of the originalities of this study was to demonstrate MFSNP as a novel derivatized "hybrid monomer" in making RPC monolithic columns with surface bound octadecyl ligands. In this respect, the RPC behavior of the monolithic column with "covalently" incorporated FNSPs having surface grafted octadecyl ligands was evaluated with alkylbenzenes, aniline derivatives and phenolic compounds. The results showed that the hybrid poly(GMA-EDMA-MFSNP) having surface bound octadecyl ligands exhibited hydrophobic interactions under reversed phase elution conditions. Furthermore, six standard proteins were baseline separated on the column using a 10 min linear gradient elution at increasing ACN concentration in the mobile phase at a flow rate of 1.0 mL/min using a 10 cm x 4.6 mm i.d. column. The relative standard deviations (RSDs) for the retention times of the tested solutes were lower than 2.1% and 2.4% under isocratic elution and gradient elution conditions, respectively. (C) 2016 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2016.03.083
Sayi :1445 Sayfa :62-67
A rapid and simple LC-MS/MS method was developed and optimized for screening and confirmation of triphenylmethane dyes including malachite green (MG), leucomalachite green (LMG), crystal violet (CV), leucocrystal violet (LCV) and brilliant green (BG) in fish muscle with skin. Leucocrystal violet D6 (LCV-D6) and leucomalachite green-D5 (LMG D5) was used as internal standards. Sample preparation is a simple procedure based on solid-liquid extraction with acetonitrile containing 1% acetic acid, followed by centrifugation and evaporation of the supernatant. The residue was dissolved in acetonitrile with 0.1% acetic acid and centrifuged prior to LC-MS/MS analysis. Chromatographic separation of analytes was performed on an Inertsil ODS-4 C18 column with ammonium acetate buffer in acetonitrile gradient. The mass detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via electrospray ionization (ESI+). The developed method was validated according to the criteria set in Commission Decision 2002/657/EC. The decision limit (CC alpha) was 0.43, 0.24, 0.33, 0.28 and 0.17 mu g kg(-1) for MG, LMG, CV, LCV and BG respectively. The detection capability (CC beta) values obtained were 0.56, 0.31, 0.43, 0.37 and 0.22 mu g kg(-1), respectively. The precision of the method, expressed as relative standard deviation (RSD) values for the within-day and inter-day laboratory reproducibility, for MG, LMG, CV, LCV and BG at the four levels of fortification (0.3, 0.5, 1, and 2 mu g kg(-1)), was less than 16 and 19% respectively. Accuracy of the method was confirmed by successful participation of a proficiency test organized by FAPAS. The method has been used for the analysis of 208 fish samples of which seven samples were found to be non-compliant containing low residues of LMG and LCV. (C) 2014 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2014.04.091
Sayi :1349 Sayfa :37-43
A simple and rapid method using liquid chromatography coupled to diode array detection (LC-DAD) was developed for the determination of acrylamide in potato-based foods at low levels. The method entails extraction of acrylamide with methanol, purification with Carrez I and 11 solutions, evaporation and solvent change to water, and cleanup with a Oasis HLB solid-phase extraction (SPE) cartridge. The final extract was analyzed by LC-DAD for quantification and by liquid chromatography coupled to mass spectrometry (LC-MS) for confirmation. The chromatographic separations were performed on a hydrophilic and a hydrophobic interaction columns having good retention of acrylamide under 100% aqueous flow conditions (k' 3.67 and 2.54, respectively). The limit of quantitation was estimated to be 4.0 mu g/kg based on the signal-to-noise ratio of 3 recorded at 226 nm. Recoveries of acrylamide from potato chips samples spiked at levels of 250, 500 and 1000 (n = 4 for each level) mu g/kg ranged between 92.8 and 96.2% with relative standard deviations of less than 5%. The results of this study revealed that a conventional LC instrument coupled to DAD can also be used accurately and precisely, as an alternative to tandem LC-MS methods for the determination of acrylamide in potato-based foods. (c) 2004 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2004.10.094
Sayi :1088 issue :1-2 Sayfa :193-199
Estimation of uncertainty of measurement is a crucial issue to achieve accurate measurement results. When the target has adverse environmental and health effects, accuracy of the results become more important. POPs are the pollutants that have toxic effects and unfortunately, there is a lack of information about uncertainty of the method for determining POPs in air samples. In this work, uncertainty calculations were carried out for PCBs, OCPs, and PAHs in air samples analyzed by using GC-MS and GC-ECD. The main dominant sources for combined uncertainty were calibration curve, recovery and repeatability. The relative uncertainties were found to be in the range of 23-52% for PCBs, 24-59% for OCPs and 23-90% for PAHs. (C) 2013 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2013.12.005
Sayi :1325 Sayfa :40-48
A generic sample preparation method for the determination of acrylamide in foods was developed. The method entails extraction with methanol, purification with Carrez I and II solutions, evaporation and solvent change to water, and cleanup with Oasis HLB solid-phase extraction (SPE) cartridge. The final extract was analyzed by liquid chromatography-mass spectrometry (LC-MS) for quantitation. The chromatographic separation was performed on ODS-3 column using the isocratic mixture of 0.01 mM acetic acid in 0.2% aqueous solution of formic acid at a flow rate of 0.6 ml/min at 25 degrees C. The recoveries of acrylamide from potato chips, biscuits and coffee ranged between 92.8 and 101.5% with relative standard deviations of 4.1% or less. The limit of detection (LOD) and the limit of quantitation (LOQ) were 2 ng/g and 6 ng/g in the basis of signal to noise ratios of 3: 1 and 9: 1, respectively. (c) 2006 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2006.01.084
Sayi :1120 issue :1-2 Sayfa :194-198
Fumed silica nanoparticles (FSNPs), were incorporated for the first time into a polymethacrylate monolithic column containing glyceryl monomethacrylate (GMM) and ethylene dimethacrylate (EDMA) in order to develop a new monolithic column for hydrophilic interaction high performance liquid chromatography (HILIC). When compared to poly(GMM-EDMA) monolithic column without FSNPs, the same monolithic column with incorporated FSNPs yielded important effects on HILIC separations. The effects of monomers and FSNPs content of the polymerization mixture on the performance of the monolithic column were examined in details, and the optimized stationary phase was investigated over a wide range of mobile phase composition with polar acidic, weakly basic and neutral analytes including hydroxy benzoic acids, nucleotides, nucleosides, dimethylformamide, formamide and thiourea. The retention of these analytes was mainly controlled by hydrophilic interactions with the FSNPs and electrostatic repulsion from the negatively charged silica surface in the case of hydroxy benzoic acids and nucleotides. The electrostatic repulsion was minimized by decreasing the pH of the aqueous component of the mobile phase, which in turn enhanced the retention of acidic solutes. Nucleotides were best separated using step gradient elution at decreasing pH as well as ACN concentration in the mobile phase. Improved peak shape and faster analysis of nucleosides were attained by a fast linear gradient elution with a shallow decrease in the ACN content of the ACN-rich mobile phase. The run-to-run and column-to-column reproducibility were satisfactory. The percent relative standard deviations (%RSDs) for the retention times of tested solutes were lower than 2.5% under isocratic conditions and lower than 3.5 under gradient conditions. (C) 2016 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2016.03.075
Sayi :1445 Sayfa :55-61
New cation exchanger monolithic stationary phases were prepared by immobilization of three different calixarene derivatives (i.e. tetracarboxylate calixarene, CLX-COO, tetrasulfonate calixarene, CLX-SO3, and tetraphosphonate calixarene, CLX-PO4) onto a monolithic cryogel support (i.e. poly(2-hydroksyethylmethacrilate-co-glycidyl methacrylate, P) and investigated with respect to preparative protein chromatography. The obtained monoliths were characterized through various techniques such as FTIR spectroscopy, isoelectric point measurements, titrimetric analyses, and mercury intrusion porosimetry. Protein retention was investigated using some model proteins (i.e. lysozyme, cytochrome c, and alpha-chymotrypsinogen A, human serum albumin, and myoglobin), and the role of modifier (i.e. NaCI) concentration and pH was thoroughly analyzed under isocratic and gradient elution conditions. Overloading experiments were also conducted to study dynamic adsorption capacity and the obtained values were found to be ranging between 3 and 8 mg/mL depending on the type of calixarene molecule. Hence, higher or comparable protein adsorption capacities were seen to be applicable on calixarene-immobilized cryogels when compared to any other functionalized cryogels in the literature. Combined with the favorable properties of these monoliths, with respect to mass transport of large molecules, these results qualify calixarene functionalized monolithic cryogels as promising stationary phases for protein preparative purification. (C) 2018 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2018.05.026
Sayi :1558 Sayfa :59-68
Atropine and obidoxime in a parenteral injection device are determined by simple HPLC method simultaneously without any pretreatment at 228 nm. The relative standard deviations (R.S.D.) were below 1.6% for the compounds. The correlation coefficient was greater than 0.999 for both compounds in the calibration range. The recoveries at 5 mg/L concentration averaged as 95% for atropine and 102% for obidoxime. The uncertainty of the measurements for atropine and obidoxime was 2.8% and 2.4%, respectively. (C) 2004 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2004.09.048
Sayi :1057 issue :1-2 Sayfa :237-239
Compared to other sub-techniques of field flow fractionation (FFF), cyclical electrical field flow fractionation (CyE1FFF) is a relatively new method with many opportunities remaining for improvement. One of the most important limitations of this method is the separation of particles smaller than 100 nm. For such small particles, the diffusion rate becomes very high, resulting in severe reductions in the CyEIFFF separation efficiency. To address this limitation, we modified the electrical circuitry of the EIFFF system. In all earlier EIFFF reports, electrical power sources have been directly connected to the E1FFF channel electrodes, and no alteration has been made in the electrical circuitry of the system. In this work, by using discrete electrical components, such as resistors and diodes, we improved the effective electric field in the system to allow high resolution separations. By modifying the electrical circuitry of the EIFFF system, high resolution separations of 15 and 40 nm gold nanoparticles were achieved. The effects of applying different frequencies, amplitudes and voltage shapes have been investigated and analyzed through experiments. (C)2014 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2014.08.097
Sayı :1365 Sayfa :164-172
A hybrid monolith exhibiting almost retention independent separation performance in hydrophilic interaction chromatography (HILIC) was obtained by one-pot photoinitiated thiol-methacrylate polymerization. Polyhedral oligomeric silsesquioxane containing methacrylate units (POSS-MA) was used as the main monomer and crosslinking agent, together with a hydrophilic ligand with two carboxyl groups, mercaptosuccinic acid (MSA) as the thiol agent and chromatographic ligand. The isocratic separation of nucleosides, nucleotides and organic acids on MSA attached-poly(POSS-MA) monolith was investigated in HILIC mode. The van-Deemter plots for obtained for nucleosides, nucleotides and benzoic acids clearly showed that there were two regions in each graph with two different slopes in the studied range of linear flow rate (i.e. 0.2-4.3 mm/s). The slope of plate height-linear, velocity curve was so small in the low linear velocity region between 0.2-2.1 mm/s while the slope in high linear velocity region between 2.1-4.3 mm/s was so higher with respect to the first region. The van-Deemter plots sketched for all analyte grous used in HILIC mode obeyed this tendency Almost "retention independent plate height behavior" was demonstrated in HILIC, using nucleotides, nucleotides or benzoic acids as the analytes in the linear velocity range of 0.2-2.1 mm/s. This behavior was explained by the porous structure of the synthesized monolith facilitating the convective transport of analytes. The variation of plate height was not retention-independent within high linear velocity range (>3.2 mm/s) when nucleosides were separated in HILIC mode. (C) 2017 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2017.04.044
Sayı :1502 Sayfa :14-23
An improved analytical method which offers rapid, accurate determination and identification of 22 amino acids in a variety of matrices, e.g. baby foods, juices, honey is reported. The amino acids were extracted from the matrixes using acidified water. Simultaneous determination of 22 underivatized amino acids was carried out by a liquid chromatography-mass spectrometry (LC/MS). A narrow-bore column allowed rapid screening and quantitative analysis by positive LC/atmospheric pressure chemical ionization (APCI) MS with only acidified mobile phase. Retention times of the 22 amino acids were in the range of ca. 0.9-7.5 min. Sample preparation without clean-up followed by fast chromatographic analysis allowed the analysis to be completed in < 25 min. (c) 2006 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2006.09.039
Sayi :1135 issue :2 Sayfa :179-185
Poly(3-chloro-2-hydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(HPMA-Cl-co-EDMA) capillary monolith was proposed as a reactive starting material with tailoring flexibility for the preparation of monolithic stationary phases. The reactive capillary monolith was synthesized by free radical copolymerization of 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl) and ethylene dimethacrylate (EDMA). The mean pore size, the specific surface area and the permeability of poly(HPMA-Cl-co-EDMA) monoliths were controlled by adjusting porogen/monomer volume ratio, porogen composition and polymerization temperature. The porogen/monomer volume ratio was found as the most effective factor controlling the porous properties of poly(HPMA-Cl-co-EDMA) monolith. Triethanolamine (TEA-OH) functionalized polymethacrylate monoliths were prepared by using the reactive chloropropyl group of poly(HPMA-Cl-co-EDMA) monolith via one-pot and simple post-functionalization process. Poly(HPMA-Cl-co-EDMA) monolith reacted with TEA-OH was evaluated as a stationary phase in nano-hydrophilic interaction chromatography (nano-HILIC). Nucleotides, nucleosides and benzoic acid derivatives were satisfactorily separated with the plate heights up to 20 mu m. TEA-OH attached-poly(HPMA-Cl-co-EDIVIA) monolith showed a reproducible and stable retention behaviour in nano-HILIC runs. However, a decrease in the column performance (i.e. an increase in the plate height) was observed with the increasing retention factor. Hence "retention-dependent column efficiency" behaviour was shown for HILIC mode using the chromatographic data collected with the polymer based monolith synthesized. (C) 2015 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2015.04.005
Sayi :1396 Sayfa :86-97
An exhaustive GC-MS acquisition study was performed, for the simultaneous analysis of natural and synthetic steroids and cholic acids (in order to insert them into the last tierce of our multiresidue analysis system), such as androsterone, beta-estradiol, transdehydroandro-sterone. transdehyroandrosterone, mestranol, dihydrotestosterone, ethinylestradiol, testosterone, norethisterone, estriol, 4-androstene-3,17-dione, gestodene, levonorgestrel, etonogestrel, coprostanol, progesterone, cholesterol, medroxyprogesterone-acetate, lithocholic acid, stigmasterol, cholic acid, chenodeoxycholic acid, beta-sitosterol, ursodeoxycholic acid, 3-hydroxy-7-ketocholic acid and dehydrocholic acid, in total 26 compounds. As novelties to the field, for the trimethylsilyl (TMS) oxime ether/ester derivatives of steroids and cholic acids, at first, a tandem mass spectrometric (MS/MS), multiple reaction monitoring (MRM) type acquisition method has been developed in a single run; also for the first time, the three acquisition techniques, the full scan (FS), the selective ion monitoring (SIM), in our case the multiple ion monitoring (MIM) and the currently optimized MRM methods, have been compared; all three, in parallel, under strictly the same derivatization/instrumental conditions, both in matrix free solutions and municipal wastewater from two Hungarian wastewater treatment plants (WWTPs). Critical evaluation of the three acquisition protocols was collated on their analytical performances and validated under the same conditions. The data of six point calibration curves for FS, MIM and MRM methods, showed that both R(2) (0.9995, 0.9858, 0.9975) and RSD (5.3, 5.8, 5.0), for two parallel derivatizations, each injected three times, proved to be independent of the acquisition processes. Whereas, for the method limit of quantification (LOQ) and the instrument limit of quantification (ILQ) values showed considerable differences. LOQ data, were decreasing in the FS, MIM, MRM line (expressed in ng/L), for all steroids and cholic acids. The same trend was determined in terms of the ILQ values. The practical utility of the optimized acquisition techniques was confirmed by the quantitation of the steroids and cholic acids contents of wastewater samples. Results confirmed the importance of the MRM acquisition method, even in comparison to the MIM one: with particular interest in selected cases: avoiding the extreme overestimation of the beta-estradiol (156-1325%) and that of the ethinylestradiol (582-831%) concentrations in the wastewater samples. (C) 2011 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2011.09.006
Sayi :1218 issue :45 Sayfa :8264-8272
This paper reports the extension of our multiresidue analysis (MA) procedure with 18 natural and synthetic steroids; permitting the identification and quantification, in total of 81 pollutants from one solution, by a single injection, as their trimethylsilyl (TMS)-oxime ether/ester derivatives, by gas chromatography-mass spectrometry (GC-MS), within 31 min. As a novelty to the field, basic researches, such as fragmentation pattern analysis and derivatization optimization studies were performed for androsterone, transdehydroandrosterone, transandrosterone, mestranol, dihydrotestosterone, ethinylestradiol, testosterone, norethisterone, estriol, 4-androstene-3,17-dione, gestodene, levonorgestrel, etonogestrel, coprostanol, progesterone, cholesterol, medroxy-progesterone-acetate, stigmasterol and beta-sitosterol. Results confirmed that (i) the TMS oxime-ether derivatives of the keto steroids provide from 1.40 times (gestodene) up to 4.25 times (norethisterone) higher responses compared to their TMS-ether ones, and (ii) the distribution of syn/anti oximes is characteristic to the ketosteroid species examined. Based on our optimized mass fragmentation, solid phase extraction (SPE) and derivatization studies separations have been performed in the total ion current (TIC) mode, identification and quantification of compounds have been carried out on the basis of their selective fragment ions. Responses, obtained with derivatized standards proved to be linear (hydroxysteroids), or have been calculated from calibration curves (ketosteroids) in the range of 1.88-750 ng/L levels. Limit of quantitation (LOQ) values varied between 1.88 ng/L and 37.5 ng/L concentrations. The most important practical messages of this work are the high androsterone (0.744-4.28 mu g/L), transandrosterone (0.138-4.00 mu g/L). coprostanol (2.11-302 mu g/L), cholesterol (0.308-41 mu g/L), stigmasterol (1.21-8.40 mu g/L)and beta-sitosterol (1.12-11.0 mu g/L) contents of influent wastewaters. beta-Estradiol (100 ng/L) and estriol (54 ng/L) were found in one influent sample, only. Reproducibilities, characterized with the relative standard deviation percentages (RSD%) of measurements, varied between 1.73 RSD% (beta-estradiol) and 5.4 RSD% (stigmasterol), with an average of 4.82 RSD%. (C) 2011 Elsevier B.V. All rights reserved.
DOI : 10.1016/j.chroma.2011.01.051
Sayi :1218 issue :14 Sayfa :1878-1890
The chromatographic separation of simple ions by a polymer gel in water was modelled as a liquid—liquid partition process. The model consists of two “homogeneous” phases, a mobile phase of pure eluent and a stationary (gel) phase of a structureless concentrated polymer solution with a few electric charges fixed within it. Thermodynamic considerations and a simplifying approximation yielded a simple description of single-salt systems, which accounted for the chromatographic behaviour of simple ions at low and high concentrations in a systematic fashion. The intoduced notion of “intrinsic distribution coefficients” of ions proved to be useful. The main mechanism of the separation ions is suggested to be the difference in the thermodynamic stabilities of individual ions in the two phases, rather than involving size-exclusion and adsorption effects.
DOI : 10.1016/s0021-9673(01)93270-4
ISSN: 0021-9673 Cilt: 511 Sayfa: 59-68
Continuous chromatography has been studied on a bunch of plastic fibres used as mobile stationary phased. The effect of fibre velocity on peak velocity was determined by elution chromatograms. The relation obtained can be used for continuous separations. It was demostrated that the decreasing theoretical plate numbers of peaks coming from moving fibre are due to the decreasing peak velocities. In spite of this the resolution increases.
This report presents simultaneous analysis of cations and anions by capillary electrophoresis (CE) in conjunction with indirect fluorescence detection using a blue light-emitting diode (LED), based on the displacement of fluorescein with anionic EDTA–metal complexes and anions. A new focusing system combined with a plastic lens and a 40× objective was developed and used effectively to focus the diverging beam of the LED on the capillary. The optimum compositions for simultaneous analysis of metal ions and anions are the samples prepared in 5 mM borate, pH 9.2, containing 2 mM EDTA and the background electrolytes (BGEs) consisting of 5 mM borate buffer, 5 μM fluorescein, and 1 μM NaCl at pH 9.2. Using this pre-capillary complexation method, the analysis of a sample containing five metal ions and eight anions was accomplished in 8 min, with the relative standard deviation values for the migration times less than 2.0%. The peak heights against the concentrations of the metal ions and anions are linear in 10–1000 and 50–2000 μM, with correlation coefficients better than 0.998, and 0.982, respectively. The limits of detection at a signal-to-noise ratio 3 of up to 14.6 μM for formate and as low as 3.7 μM for Ni2+. The results of the analyses of pond water and a Chinese herbal soup present the advantages of this method, including simplicity, rapidity, reproducibility, and low costs.
A method for the preparation of gaseous calibration mixtures with defined contents of standard substances is described. An accurately controlled stream of gas (e.g., nitrogen) is drawn at a low flow-rate through a thermostated container filled with a chromatographic support impregnated with the standard substance, thus generating a continuous stream of saturated vapour of the substance. This stream is diluted in a mixing chamber with a large stream of pure gas, and a small fraction of the dilute mixture, separated by means of a splitter, is again diluted with a large stream of pure gas in another mixing chamber. In this two-stage dilution procedure it is possible to prepare mixture containing standard substances at parts per billion concentrations with an error of about 4%. Mixtures containing several standards are obtained through use of a separate saturator for each standard; the concentration ratio of two standard substances can be set to within the range 1:1 to 1:106.
Lipophilicity (logP) represents one of the most studied and most frequently used fundamental physicochemical properties. At present there are several possibilities for its quantitative expression and many of them stems from chromatographic experiments. Numerous attempts have been made to compare different computational methods, chromatographic methods vs. computational approaches, as well as chromatographic methods and direct shake-flask procedure without definite results or these findings are not accepted generally. In the present work numerous chromatographically derived lipophilicity measures in combination with diverse computational methods were ranked and clustered using the novel variable discrimination and ranking approaches based on the sum of ranking differences and the generalized pair correlation method. Available literature logP data measured on HILIC, and classical reversed-phase combining different classes of compounds have been compared with most frequently used multivariate data analysis techniques (principal component and hierarchical cluster analysis) as well as with the conclusions in the original sources. Chromatographic lipophilicity measures obtained under typical reversed-phase conditions outperform the majority of computationally estimated logPs. Oppositely, in the case of HILIC none of the many proposed chromatographic indices overcomes any of the computationally assessed logPs. Only two of them (logkmin and kmin) may be selected as recommended chromatographic lipophilicity measures. Both ranking approaches, sum of ranking differences and generalized pair correlation method, although based on different backgrounds, provides highly similar variable ordering and grouping leading to the same conclusions.
DOI : 10.1016/j.chroma.2014.12.073 Anahtar Kelimeler :
Lipophilicity, Multivariate data analysis, Sum of ranking differences, Generalized pair correlation method, High-performance liquid chromatography, PC principal component, principal component, SRD sum of ranking (absolute) differences, sum of ranking (absolute) differences, CRRN validation of the SRD procedure: comparison of Ranks by Random Numbers, validation of the SRD procedure: comparison of Ranks by Random Numbers, GPCM generalized pair correlation method (for explanation of the abbreviations see in the text)., generalized pair correlation method (for explanation of the abbreviations see in the text).
ISSN: 0021-9673 Cilt: 1380 Sayfa: 130-138
The effect of the channel width on the performance of separation by micro-thermal field-flow fractionation (micro-TFFF) of the carboxylated polystyrene latex particles was studied by using the particles in diameter range from 100 nm to 3800 nm. It has been shown that the retention order follows the anticipated polarization, steric, and focusing mechanism in the corresponding size range and under the specific conditions, appropriate to each channel thickness. However, the attractive interactions of the particles with the accumulation wall can complicate the separation as has been proven by the experiments carried out by using the carrier liquids of different ionic strengths. Three channel thicknesses (0.025, 0.100, and 0.250 mm) were tested thus imposing the volumes of micro-channels of roughly 9, 37, and 92 μl. Such an experimental investigation has never been performed with respect to the applicability of the TFFF within an extended range of molar masses or particle sizes. The advantages and drawbacks of different channel widths are discussed with respect to the performance of separation of micro-TFFF but also by taking into account the practical requirements of the construction of the micro-TFFF channel. The principal finding is that very thin channel ( w = 0.025 mm) substantially reduces the range of particle sizes or polymer molar masses that can effectively be separated due to the mixed separation mechanism, steric exclusion being effective from smaller particle size. The found dependence of the resolution on the imposed experimental conditions including the channel width has allowed the elucidation of some peculiar results published in the literature, which were contradictory with regard to the known theoretical and experimental findings.
Manganese is a trace element known to activate many enzymes involved in metabolic processes and it shows protective function against oxidative stress. On the other hand, increased Mn levels are known for damaging the central nervous system, resulting in motoric abnormalities and psychic disorder. Such additional Mn exposure can cause an “Mn overflow” in the liver, accompanied by production of specific (labile) Mn transporters (Mn-species). The speciation of these Mn-compounds is still unknown but they are believed targeting the brain. The aim of this paper was to develop a speciation method for manganese species in liver extracts, which allows to speciate the compounds quickly and with minimal risk of species alteration. Capillary electrophoresis (CE)–inductively coupled plasma mass spectrometry (ICP-MS) offers a valuable tool as analytes are not in contact to a stationary phase which probably affects species stability. Separation usually is fast and ICP-MS detection is element specific and sensitive. The paper describes the set-up and optimization of the hyphenated technique, optimization of separation according to pH and finally the Mn speciation of a liver extract. Several Mn species were found, such as arginase, Mn-transferrine, Mn-albumine and some more. The detection limit of the method was determined at 1.1 μg Mn/L independent on the species.
Technical waxes and paraffins were investigated using supercritical fluid chromatography (SFC), matrix-assisted laser-desorption/ionization mass spectrometry (MALDI-MS) and size-exclusion chromatography (SEC). SEC enables the simultaneous determination of molecular masses up to high values and molecular mass distributions. The resolution of homologous species, however, is poor. In this respect the use of SFC is advantageous. Proper resolution of homologues may be provided up to Mr∼1200 without great difficulty. To compare these chromatographic results MALDI-MS was applied for the determination of molecular masses and mass distributions in technical waxes for the first time. Using reflectron mode excellent MALDI mass spectra could be achieved in the molecular mass range up to 1000 Da. The mean values of the molecular masses calculated by MALDI-MS were in sufficient agreement with those of SFC. In the linear mode of MALDI-MS molecular masses could be determined to nearly 3000 Da. Beyond this mass range SEC still remains the method of choice. Advantages and diffulties of the used methods are discussed in this paper.
DOI : 10.1016/0021-9673(95)01255-9 Anahtar Kelimeler :
Molecular mass determinations, Molecular mass distributions, Waxes, Paraffins
ISSN: 0021-9673 Sayı: 1 Cilt: 732 Sayfa: 111-117
Nitrazepam in plasma was determined by gas-liquid chromatography with a nickel-63 electron-capture detector, unchanged by a direct method and also by a hydrolysis method. The extraction in the direct method was carried out with benzene-dichloromethane (90:10) and in the hydrolysis method with diethyl ether. The hydrolysis was performed with 6 N sulphuric acid. The hydrolysis product was extracted with toluene-n-heptane-ethyl acetate (80:20:5) directly from acid. Thus the commonly used change in pH was omitted. Nitrazepam concentrations in plasma were determined in 10 healthy volunteers after two oral doses (5 and 10 mg); 0.5 ml of plasma was used for each determination and clonazepam, methylbromazepam and methylnitrazepam were used as internal standards. The recoveries of the methods are almost quantitative (>96%). The two methods are clinically comparable. The high sensitivity and specificity make these methods useful in clinical determinations of nitrazepam in plasma. Advantages and disadvantages of both methods are discussed.
High-speed counter-current chromatography (HSCCC) has been successfully applied to the separation of the ivermectin components. A 25-mg quantity of the sample was separated using a two-phase solvent system of n-hexane-ethyl acetate-methanol-water (19:1:10:10, v/v). The fractions were analyzed by high-performance liquid chromatography, nuclear magnetic resonance, and fast-atom bombardment mass spectrometry. The separation yielded 18.7 mg of 99.9% pure ivermectin B1a, 1.0 mg of 96.0% pure ivermectin B1b, and 0.3 mg of 98.0% pure avermectin Bla (precursor of ivermectin).