Dimethylformamide as a mobile phase component in reversed-phase liquid column chromatography on octadecylsilica

Characterization of Klason lignins by reversed-phase high-performance liquid chromatography using wide-pore octadecylsilica and stepwise gradients of dimethylformamide in water

RP-HPLC using stepwise gradients of N,N-dimethylformamide (DMF) in a phosphate-buffered (pH 3.00) aqueous mobile phase and a wide-pore (30 nm) octadecylsilica column has been applied to the analysis of a variety of lignins--organocell lignin, dioxane lignin, Björkman lignin, and Klason lignins from both softwoods and hardwoods, respectively, in order to demonstrate the usefulness of the approach for their characterization. Tandem combination of spectrophotometric diode array detection and fluorimetric detection was used to acquire more detailed information about the chromatographic behavior of lignins. The results show that a ten-step gradient can reveal distinct features of lignins and humic substances. Combination of good solvating properties of DMF for lignins together with a wide-pore RP sorbent improves surface interactions of the analytes and suppresses the influence of size exclusion effects. Thus it provides reproducibility of characterization profiles and robustness of the method. The calculated repeatability of the retention time of selected peaks was +/- 0.46% RSD. The reproducibility of the data within one week (set of seven data) was +/- 1.1% RSD. These data are also representative of the other well-shaped peaks of analyzed substances.

Novel stepwise gradient reversed-phase liquid chromatography separations of humic substances, air particulate humic-like substances and lignins

RP-HPLC using stepwise gradients of dimethylformamide (DMF) in buffered aqueous mobile phase and a wide-pore (30 nm) octadecylsilica column has been applied to the analysis of soil, peat and air particulate humic and humic-like substances (HSs), as well as lignin, in order to demonstrate the usefulness of the approach for their characterization even at trace concentration level. Tandem combination of spectrophotometric (DAD) and fluorimetric detection was used to get more detailed information on chromatographic behaviour of HSs. The results showed that ten-step gradient can induce distinct features of HSs and lignins. Combination of very good DMF solvating and disaggregating properties for HSs and lignins together with wide pore RP sorbent improves surface interactions of the analytes and suppresses influence of size exclusion effects. Thus it provides reproducibility of characterisation profiles and robustness of the method. Very good reproducibility of retention times (from +/-0.12 to +/-0.36% RSD), of peaks enforced by the step gradient shape supports well defined characterization and/or fractionation of HSs. Evaluated limit of quantitation (S/N = 10) of selected soil humic acid working standard using fluorimetric detection (ex.470 nm/em.530 nm) was 9.7 microg/ml. This corresponds to 0.5 microg of the humic acid per injection. Calculated limit of detection (S/N = 3) was 3.3 microg/ml, what corresponds to 0.15 microg of the humic acid per injection and enabled determination of 0.1% (m/m) humic-like substances in 20 mg of air particulates under defined rules and conditions.

Quantification of desferrioxamine, ferrioxamine and aluminoxamine by post-column derivatization high-performance liquid chromatography. Non-linear calibration resulting from second-order reaction kinetics

Desferrioxamine B is widely used as therapeutic agent for removal of excess body iron and, more recently, for removal of aluminium. A HPLC-based method for direct sensitive and reliable determination of ferrioxamine, desferrioxamine, aluminoxamine and related metabolites has been developed for use in pharmacokinetic studies. The method consists of complete separation of the analytes by an optimized mobile phase avoiding conversion of desferrioxamine to ferrioxamine by the analytical system and overcoming problems due to peak tailing properties of desferrioxamine. A post-column derivatization reaction with colourless fluoro-complexed iron converts all iron free species to ferrioxamine and allows quantification at 430 nm avoiding interference of UV-absorbing coelutes. This reaction might be of interest for other analytical procedures concerning iron chelators. The influence of the post-column reaction system on the column plate number is characterized. As the reaction rate of desferrioxamine and aluminoxamine with iron(III) is of second-order kinetics, a quadratic calibration function is observed, resulting from a compromise between residence time and peak broadening. A solid-phase extraction procedure is presented for extraction of the analytes from plasma. Limits of detection (S/N ratio of 3) were determined as 1.95 ng for ferrioxamine, 3.9 ng for aluminoxamine and 15.7 ng for desferrioxamine, expressed as on-column load. A new iron-free metabolite was identified with fast atom bombardment-mass spectrometry as N-hydroxylated desferrioxamine.

Simultaneous quantification of cefotaxime, desacetylcefotaxime, ofloxacine and ciprofloxacine in ocular aqueous humor and in plasma by high-performance liquid chromatography

Cefotaxime, given intravenously, is currently used as a broad-spectrum antibiotic for prophylaxis of intra- and postoperative infections in ocular lens surgery. A proposed therapeutic and economic alternative is the use of orally active fluoroquinolone ofloxacine as prophylactic agent. A HPLC method was developed for determination of both antibiotics in ocular aqueous humor and plasma in order to optimize dosage for safe surpassing minimal inhibitory concentration in the humor compartment. For plasma determinations a solid-phase extraction procedure was used with ciprofloxacine as internal standard. Detection limits for direct HPLC-analysis of ocular aqueous humor was 0.08 microg/ml for all compounds, whereas in plasma 0.31 microg/ml could be determined after solid-phase extraction.

Adenine derivatives as phosphate-activating groups for the regioselective formation of 3',5'-linked oligoadenylates on montmorillonite: possible phosphate-activating groups for the prebiotic synthesis of RNA

Methyladenine and adenine N-phosphoryl derivatives of adenosine 5'-monophosphate (5'-AMP) and uridine 5'-monophosphate (5'-UMP) are synthesized, and their structures are elucidated. The oligomerization reactions of the adenine derivatives of 5'-phosphoramidates of adenosine on montmorillonite are investigated. 1-Methyladenine and 3-methyladenine derivatives on montmorillonite yielded oligoadenylates as long as undecamer, and the 2-methyladenine and adenine derivatives on montmorillonite yielded oligomers up to hexamers and pentamers, respectively. The 1-methyladenine derivative yielded linear, cyclic, and A5'ppA-derived oligonucleotides with a regioselectivity for the 3',5'-phosphodiester linkages averaging 84%. The effect of pKa and amine structure of phosphate-activating groups on the montmorillonite-catalyzed oligomerization of the 5'-phosphoramidate of adenosine are discussed. The binding and reaction of methyladenine and adenine N-phosphoryl derivatives of adenosine are described.

Convergent solid-phase peptide synthesis. 12. Chromatographic techniques for the purification of protected peptide segments

The purification of a range of protected peptide segments has been carried out using modified reversed-phase chromatographic techniques in which DMF was added to the water and acetonitrile mixtures used as eluents. The purity of the recovered peptides was excellent and recoveries were high in all cases, even for longer hydrophobic segments. In several cases purifications were carried out on the hundreds of milligrams scale. For protected peptide segments containing Met, protection as the sulfoxide avoids its unwanted alkylation and oxidation, and the increased overall polarity can be useful in the purification of protected peptides incorporating this residue.

High-performance liquid chromatographic analysis of glutathione and its thiol and disulfide degradation products

A rapid and sensitive high-performance liquid chromatographic method for quantitation of picomole levels of glutathione, glutathione disulfide, cysteine, cystine, cysteinylglycine, cysteinylglycine disulfide and cysteine glutathione-mixed disulfide in biological samples is described. The compounds were separated isocratically on a reversed-phase column by ion-pair chromatography. The mobile phase consisted of an aqueous buffer containing 0.1 M monochloroacetic acid and 3.3 mM 1-heptanesulfonic acid (pH 2.60)-methanol-N,N-dimethylformamide (96.5:3.0:0.5). After chromatographic separation, the disulfides were reduced by a potential (-1.0 V) from a battery, with subsequent detection of all thiols by electrochemical oxidation (+0.15 V) with a dual gold-mercury electrode. Thiol and disulfide concentrations were determined in tissue extracts (liver and kidney) and fluids (bile and plasma) from control rats and rats treated with acivicin, an inhibitor of gamma-glutamyltranspeptidase. A marked increase in biliary glutathione concentration was observed in treated animals with a corresponding decrease in cysteine and cysteinylglycine concentrations. The results demonstrate that this method is useful for measuring glutathione and its degradation products in tissues and fluids.