摘要:

The retention behaviors of polybutadiene-coated titania stationary phase (PBD-TiO2) are investigated by the use of linear solvation energy relationships (LSERs) of 21 solutes. The logarithmic capacity factors measured on PBD-TiO2(logk′ (PBD-TiO2)) in a methanol-water (80:20, v/v) mobile versus the solutes' four interaction descriptors, the McGowan characteristic molar volume (Vx), dipolarity/polarizability (Π2*), effective or overall hydrogen bond donor acidity (Σα2H) and hydrogen bond acceptor basicity (Σβ2H) are analyzed by multiple regression analysis and compared to conventional bonded reversed stationary phase. We find that PBD-TiO2is very similar to conventional bonded reversed stationary phase. The descriptors, Vx, π2* and Σβ2Hare the most important parameters governing the retention, as they represent more than 96.62% of the log k′ variation. Finally, we come to the conclusion that the retention of PBD-TiO2is a partition mechanism.

ISSN:1082-6076    

DOI:10.1081/JLC-100100406

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Several steroidal hormones with an α,β-unsaturated carbonyl group sensitized the fluorescence of terbium(III) ions: medroxyprogesterone, medroxyprogesterone acetate, methyltestosterone, nandrolone, nandrolone decanoate, progesterone, testosterone, testosterone enanthate, and testosterone propionate, but other steroids which have this chromophore did not give any signal: clostebol acetate, dehydrotestosterone, dydrogesterone, methandienone, and methenolone enanthate. Sensitized fluorescence was used to detect the steroids when eluted with micellar mobile phases of sodium dodecyl sulphate (SDS)-acetonitrile and SDS-pentanol containing 0.01 M Tb(III), with 245 nm and 545 nm as excitation and emission wavelengths, respectively. The micelles favour the fluorescence process due to proximity of donor and acceptor, and shielding of the Tb(III) ions from the aqueous medium. Signal intensity increased linearly with the concentration of Tb(III), but decreased with acetonitrile and pentanol. The concentration of organic solvent in the mobile phase should, therefore, be limited. Mobile phases of 0.075 M SDS-12.4% acetonitrile and 0.13 M SDS-4.5% pentanol offered the highest sensitivities, but only pentanol permitted the elution of the most hydrophobic steroids at adequate retention times. With this mobile phase, the limits of detection were in the 0.07–0.2 μg/mL range. The sensitivities did not change in the 25–60°C range, but the efficiencies of the chromatographic peaks were larger at higher temperature, and consequently, the resolution was improved.

ISSN:1082-6076    

DOI:10.1081/JLC-100100407

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Partial Least Squares (PLS) and Principal Component Regression (PCR) methods were applied to the simultaneous determination of a mixture of twelve pesticides by high performance liquid chromatography (HPLC). Calibration models at two different wavelengths were developed to resolve mixtures of the pesticides with overlapping chromatographic peaks. The first model carried out at 205 nm, as first detector compromise wavelength, yielded satisfactory sensitivity and selectivity for estimation of the concentration of iprodione, procymidone, triadimefon, and vinclozolin. The other model at 250 nm, as second detector compromise wavelength, was used for estimation of chlorothalonil, clorfenvinphos, fenamiphos, parathion-methyl, parathion-ethyl, and triazophos. However, two pesticides of the mixture, malathion and tebuconazole, showed bad prediction ability and were not determined, perhaps owing to their low signal relative to the other compounds. Both calibration models were evaluated by predicting the concentration of independent test set samples, and were successfully applied to the determination of these pesticides in groundwater samples. In all cases the PLS calibration method showed superior quantitative prediction ability than the PCR method.

ISSN:1082-6076    

DOI:10.1081/JLC-100100408

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Regioselective functionalization of 2,4,5,6-tetrachloro-1,3-dicyanobenzene (TCDCB) by nucleophilic substitution of the chlorine atom at C(4) for N-L-α-amino acid residue enables preparation of new chiral selectors (1-5). Their binding to aminopropyl silica gel afforded new brush-type chiral stationary phases (CSP-1–CSP-4). Chiral stationary phasesCSP-5andCSP-6that comprise dipeptide units L-Ala-L-Pro and L-Ala-L-Ala, respectively, were obtained by the solid-state coupling of C(4)substituted derivatives of 2,5,6-trichloro-1,3-dicyanobenzenes4and5to γ-L-alanylaminopropyl silica gel. Best resolution for some of 23 test racemates was achieved withCSP-4andCSP-6. This study reveals hydrogen bonding via a sterically exposed amide group and a π-π type interaction via an π-acid persubstituted benzene ring in these CSPs as the main contribution to chiral recognition.

ISSN:1082-6076    

DOI:10.1081/JLC-100100409

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The partition coefficients of 10 selected sulfonamides in the system octanol-water (Pow) and their retention coefficients (k) in RP HPLC with anion micellar mobile phase were determined. The mechanism of retention of the sulphonamides studied was analysed depending on the concentration of sodium dodecylsulphate in the mobile phase and pH of the latter. Relationship between the partition coefficients and retention coefficients was established. It was shown that apart from Pow, a measure of the hydrophobic character of such amphoteric compounds as the sulfonamides studied, could be the values of the retention coefficient determined at pH of the isoelectric point.

ISSN:1082-6076    

DOI:10.1081/JLC-100100410

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A high-performance liquid chromatographic (HPLC) assay has been designed for the quantitative determination of polymer-bound paclitaxel (after hydrolytic release of paclitaxel from the polymer) and free paclitaxel in human plasma after intravenous administration of the antitumor polymer-drug conjugate PNU166945.

ISSN:1082-6076    

DOI:10.1081/JLC-100100411

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A simple, specific, and accurate HPLC assay method is presented for the simultaneous measurement of the calcium antagonists nifedipine and verapamil in rat plasma. The plasma sample was deproteinized by treatment with an equivalent volume of an internal standard solution (nicardipine hydrochloride in acetonitrile containing 0.1% of perchloric acid), followed by brief centrifugation. A 50 μL aliquot of the clear supernatant was analyzed on a Microsorb-MV C18, 5 μm, column using a mixture of acetonitrile-methanol-0.01 M phosphate buffer pH 5.2 (55:15:30) as the mobile phase. At a flow rate of 1 mL/min and detection at 235 nm, nifedipine, verapamil, and nicardipine were observed to elute at about 3.4 min, 6.4 min, and 9.8 min, respectively. Detector responses were linearly related to concentrations of nifedipine in the range 0.2–1 μg/mL, and of verapamil between 0.4–2 μg/mL. As little as 0.05 μg/mL of nifedipine and 0.08 μg/mL of verapamil were accurately measured by the proposed method. Mean drug recoveries from rat plasma samples spiked with 0.25–1 μg/mL of nifedipine and 0.5–2 μg/mL of verapamil was in all cases >95% (range 97.9–98.3%, n = 5, for nifedipine; 95.7–97.1%, n = 5, for verapamil). The method was found to be well suited for assessing the plasma pharmacokinetics of the title drugs following their oral and intraperitoneal coadministration to rats.

ISSN:1082-6076    

DOI:10.1081/JLC-100100412

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A correlation between the stoichiometric parameterZin the stoichiometric displacement model for retention (SDM-R) and the parameter S (denoted Smin the new correlation) in Snyder's empirical equation for isocratic elution reversed-phase high performance liquid chromatography (RPLC) was derived with Taylor translation. The correlation is Sm= Z/(2.3Φm), where Φmis the intermediate value of the activity of the stronger organic solvent in the mobile phase. With the correlation, a more accurate conversion between Z and S can be made, and the physical meaning of the empirical parameter S can be explained by means of that of parameter Z. The correlation was validated with experiment data and data from the literature for a variety of RPLC systems with different solutes and mobile phases. The results indicated that for all solutes, especially for homologues, and mobile phases, a good linear relationship exists between the two parameters. The values of S and Smwere generally found to be similar, but the accuracy of S was generally influenced by the changing composition of the mobile phase. The reason why Smis more accurate and easily obtained than Sg(the S value obtained from two or more gradient runs) was also explained.

ISSN:1082-6076    

DOI:10.1081/JLC-100100413

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Faster and more sensitive analysis of water that is contaminated by human fecal matter is very important for public health. The current microbiological methods to assess water quality do not meet this need. Alternate non-microbial human fecal indicators have been proposed by various researchers. The high performance liquid chromatography (HPLC) analysis with photodiode array detection (PDA) of three human fecal indicators, caffeine, urobilin, and coprostanol was developed. Both caffeine and urobilin were analyzed simultaneously using a linear gradient protocol and monitored at 270 nm and 480 nm. The analysis gave linearity and limit of detection down to hundredths of μg/mL.

ISSN:1082-6076    

DOI:10.1081/JLC-100100414

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor