Shielded Hydrophobic Phase for Direct Sample Analysis: Preliminary Study for the Analysis of Phenobarbital for Potential Neonatal and Pediatric Drug Monitoring

Direct injection HPLC method for the determination of selected benzodiazepines in plasma using a Hisep column

A direct plasma injection HPLC method has been developed for the determination of selected benzodiazepines (nitrazepam, clobazam, oxazepam, lorazepam). The method uses an analytical hydrophobic shielded phase (Hisep) column equipped with a Hisep guard column, are easy to perform and requires 20 ul of a filtered plasma sample. The chromatographic run time is less than 15 min using a mobile phase of 15:85 v/v acetonitrile-0.18 M ammonium acetate pH 2.5. The method is good for 175 injections before replacement of the guard column. The method was linear in the range 0.5-18 ug ml(-1) (r>0.99, n=6) for the analytes with R.S.D. less than 10.82%. Interday and intraday variability were found to be less than 14%. The limits of detection and quantitation were 0.16 (s/n>3) and 0.5 ug ml(-1) (s/n>10), respectively, for each of the four benzodiazepines.

Direct observation of the separation process by the chromato-videoscope

Separation process in a liquid chromatographic column were visualized and analyzed by a developed chromato-videoscope. The migration aspects were evaluated with successively obtained densitograms. In reversed-phase chromatography, the band widths of each solute band were almost equal fore both weakly and strongly retained solutes when compared at the same column position (the same migration distance in the column). In the gradient elution mode, the position of the solute band showed that the migration velocity of the solute band changed gradually according to changes in solvent composition. The drug trapping process to BSA- coated ODS packings for direct injection of biological fluid was also observed. In the absence of BSA from the sample solution, the drug molecules were trapped in a narrow band. However, at higher BSA concentrations in the sample solution, a broader band shape was observed. This band broadening shows how the drug molecules were retained on the protein.

High-performance liquid chromatography using on-line solid-phase extraction: determination of furosemide in human serum

An on-line solid-phase extraction technique based on column switching (heart-cutting) was developed for direct injection analysis of furosemide in human serum. In order to minimize the influence of deterioration in pre-treatment column efficiency, which was caused by protein precipitation with repeated injections of serum, furosemide was completely enriched at the top of the analytical column by ion-pair formation with tetra-n-butylammonium ion during heart-cutting. The robustness of the established on-line solid-phase extraction system was confirmed under routine conditions. As a result, almost comparable chromatograms could be obtained even though 50 repeated injections of a 100-microliter volume of serum were carried out using one pre-treatment column. The linearity of the calibration curves was demonstrated by the correlation coefficient which was greater than 0.99999 (5-1000 ng/ml). The relative errors and C.V. of quality control samples were within 4.00 and 5.88%, respectively (furosemide concentrations: 5, 100 and 1000 ng/ml).

Hydrophilic shielding of hydrophobic, cation- and anion-exchange phases for separation of small analytes: direct injection of biological fluids onto high-performance liquid chromatographic columns

Shielded hydrophobic phases (SHPs) have an external hydrophilic network that prevents larger protein molecules from interacting with hydrophobic zones. Smaller analytes are not sterically hindered from interacting with the hydrophobic zones and are retained. This mechanism allows the separation of the proteins from the analytes of interest. SHPs have been shown to be useful for the direct-injection analysis of drugs in biological fluids. In this paper, two kinds of shielded phases are discussed: bonded micellar phases and embedded polymeric phases. For some compounds of interest, the hydrophobic retention and selectivity is insufficient to obtain the desired resolution. To increase selectivity without affecting protein exclusion, shielded phases were prepared with ion-exchange groups added to the hydrophobic zones. Such modified phases with cation-exchange and anion-exchange capabilities were examined for additional selectivities. Usage of these additional selectivities will be demonstrated to achieve better analysis and resolution for basic, acidic, and neutral compounds.

Mobile phase versus stationary phase approaches to the direct injection of biological fluids in liquid chromatography

The liquid chromatographic analysis of drugs in urine through direct injection without any sample pretreatment was extended to micellar chromatography with nonionic surfactants, the Pinkerton ISRP column and the shielded hydrophobic phase (Hisep) column. The feasibility of using each was demonstrated through the determination of the diuretic, hydrochlorothiazide, in urine. Good separation, recovery, precision and linearity, and adequate limits of detection were obtained for this analysis with all three techniques. The advantages and limitations of the mobile phase approach of micellar chromatography and the two stationary phase approaches are discussed for the direct injection of urine as well as other biological fluids.

Novel strategies for clinical drug analysis with new column technology in liquid chromatography

Clinical drug analysis has been the focus of much attention and controversy because of the increase in substance abuse testing of addicts, patients, employees and others, in addition to the rapidly growing fields of therapeutic drug monitoring and clinical toxicology. This review focuses on the latest methodological and technological advances in liquid chromatography (LC) as it is applied to clinical drug analysis. Based on the author's experience, key chromatographic parameters such as carbon load, functionalities and temperature are proposed for the separation of structurally similar metabolites and for resolving chromatographic interferences by other drugs and metabolites. Novel sample preparation for cyclosporine and gradient elution of its metabolites are reviewed, followed by an update on monitoring of 3'-azido-3'-deoxythymidine with emphasis on automated sample preparation. Various approaches of direct sample analysis are advocated for increased efficiency as a result of minimal sample preparation and potential advantages such as decreased exposure of personnel to infectious samples. An update of microbore LC indicates that 2-mm columns may be readily used for clinical paediatric and neonatal analysis without dedicated chromatographs. Potential applications of multidimensional-multimodal chromatography include analyses of a cocaine impurity, anticonvulsants, antidepressants, and five ingredients of a common cold medication.