Biomedical subjects

Michal Halama

Publications and source records attributed to Michal Halama.

4 recordsLinked to original sources

PubMed2005

HPLC determination of lincomycin in premixes and feedstuffs with solid-phase extraction on HLB OASIS and LC-MS/MS confirmation.

A rapid clean-up procedure based on solid-phase extraction (SPE) and HPLC determination of lincomycin in premixes with UV detection is described. After extraction of lincomycin from premix with extraction solvent the extract is applied to OASIS HLB column treated with methanol and water. Lincomycin is eluted with methanol and effluent is analysed on analytical column (phenyl) using mobile phase consists 0.2% phosphoric acid in water and acetonitrile (875:125, v/v). Detection is performed at 208 nm. Quantitation is carried out using external standard. The mean recovery of lincomycin was 105.0+/-7.3%, in concentration range of 250-750 mg kg(-1), and 99.8+/-3.7%, in concentration range of 10,000-150,000 mg kg(-1). The limit of determination, based on a signal-to-noise ratio of 10:1, was 5.2 mg kg(-1). LC-MS/MS confirmation of lincomycin is also presented. Identification was performed by monitoring two pairs of multiple reaction monitoring ions from the parent ions (m/z 407.2-->126.1 and 407.2-->359.2) at the defined retention time window and by matching of the specific tolerance of relative abundance of major ions as stated in the European Union Commission Decision 2002/657/EC.

Animal Feed↗

PubMed2005

Phase system selectivity and two-dimensional separations in liquid column chromatography.

Correlations between the separation selectivity in aqueous and non-aqueous reversed-phase systems and in normal-phase LC systems were investigated for samples containing different numbers of two repeat structural elements. Such samples are best separated in "orthogonal" two-dimensional chromatographic systems, showing selectivity for one type of the repeat structural element only in the first dimension and for the other structural element only in the second dimension. The number of resolved compounds improves as the degree of orthogonality of the separation systems increases with decreasing correlation between the selectivities for the sample structural distribution in the two dimensions. Orthogonal systems with non-correlated selectivities for each repeat structural element provide the highest number of separated peaks and regular arrangement of the peaks over the two-dimensional retention space according to the individual structural element distribution and the best use of the available peak capacity. Fully orthogonal systems are difficult to find in practice. Partially orthogonal system with correlated selectivities for one structural type distribution, but with one system non-distinguishing the distribution for the other structural element are still useful for the two-dimensional separations. The correlations between the selectivities for repeat regular structural increments were employed to evaluate the suitability of phase systems for two-dimensional HPLC separations. The selectivity correlation in various reversed-phase and normal-phase systems was evaluated for two sample types: (1) Various RP columns show significantly inversely correlated selectivities for acyl lengths and numbers of double bonds distribution, but the differences in the double bond selectivity can be used for practical separations of triacylglycerols with the same equivalent carbon numbers. (2) Synthetic EO-PO block (co)oligomers with two-dimensional distribution of oxyethylene and oxypropylene monomer units were separated according to the two distribution types using on-line two-dimensional reversed-phase-normal-phase LC with a C18 column in the first dimension and an aminopropyl silica column in the second dimension.

Chromatography, Liquid↗

PubMed2004

Naphthalene sulphonic acids--new test compounds for characterization of the columns for reversed-phase chromatography.

Non-substituted naphthalene sulphonic acids are strong acids, which are completely ionised in aqueous and aqueous-organic solutions. Because of repulsive electrostatic interactions, they are more or less excluded from the pores of the column packing materials commonly used in reversed-phase chromatography. The ionic exclusion can be suppressed by increasing the ionic strength of the mobile phase. In aqueous sodium sulphate solutions, very good selectivity was observed for isomeric naphthalene di- and tri-sulphonic acids, allowing reversed-phase separations of these strongly ionic compounds without addition of ion-pairing reagents to the mobile phase. The retention of the isomeric acids increases proportionally to the dipole moment, which can be explained by its effect on increasing exposure of the naphthalene ring to hydrophobic interactions with the non-polar stationary phases. Chromatographic behaviour of isomeric naphthalene di- and trisulphonic acids was investigated on 25 different columns for reversed-phase chromatography. The elution order of the isomers is the same on all the columns, but very strong stationary phase effects were observed on the retention and on the band asymmetry, depending on polar interactions with residual silanol groups and other polar adsorption centres in the stationary phases. These effects are independent of the organic solvents, as the tests are performed in purely aqueous mobile phases and allow classification of the columns into several groups.

Chromatography, High Pressure Liquid↗

PubMed2004

Stationary-phase effects in gradient high-performance liquid chromatography.

The type of the stationary phase for reversed-phase liquid chromatography significantly affects the sample polarity range that can be covered using gradients of organic solvents in water. The polarity range available for gradient separations of samples containing compounds differing in the lipophilic parts of the molecules can be characterized by "gradient lipophilic capacity", Pl, based on the retention of standard compounds with a repeat lipophilic structural unit, such as a methylene group. The gradient lipophilic capacity is also suitable to characterize the separation possibilities of the columns in non-aqueous reversed-phase gradient elution of strongly non-polar compounds, such as triacylglycerols. In the same way, the suitability of various columns for reversed-phase gradient separations of oligomers can be characterized by "gradient oligomer capacity", as demonstrated in the example of oligo(ethylene glycols). To enable a comparison of the properties of stationary phases independent of column efficiency and dimensions, the gradient lipophilic capacity or the gradient oligomer capacity should be normalized for a "standard" column plate number, gradient range and volume (in column hold-up volume units). The gradient lipophilic capacity or the gradient oligomer capacity and the number of compounds that can be resolved during a gradient run decrease as the initial concentration of the strong solvent in the mobile phase increases and (or) the gradient time decreases. These quantities can be used to select a suitable column and to adjust the optimum gradient profile (the initial composition of the mobile phase and the gradient steepness) with respect to the time of analysis and the number of oligomers or other compounds with regular repeat structural groups that can be resolved during the gradient run.

Chromatography, High Pressure Liquid↗