This focusing review summarizes our recent works on the dissemination of capillary liquid chromatography through various approaches, i.e. simple stepwise-gradient elution system, on-line sample enrichment system, alternate-pumping recycle chromatography system, on-line immobilized-enzyme reactor, development of novel stationary phases, etc. Capillary liquid chromatography saves energy and waste, and it possesses several advantages over the conventional liquid chromatography; however, it has not been much popularized since its appearance and most users still prefer to use conventional liquid chromatography if there is a choice between them. Our research focuses on, but not limited to, developing versatile capillary liquid chromatography systems that are not only environmental-friendly but also user-friendly, and novel stationary phases that could be operated under mixed modes conditions by manipulating the eluent, which are applicable to real samples analyses and will therefore eventually switch the users from “conventional” to “capillary”.
A novel and selective extraction method for nucleotides (AMP, ADP, ATP, GMP, GDP, and GTP) has been developed. In this study, we employed liquid-liquid based fluorous biphasic extraction system in the presence of a 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecylamine (HFUA) as an ion-pair reagent. The ion-pairs between nucleotides and HFUA were selectively extracted to a mixture of tetradecafluorohexane and 1H,1H,2H,2H-tridecafluoro-1-n-octanol (3:1, v/v) as fluorous solvent via the affinity of perfluoroalkyl-containing compounds with each other, i.e. fluorous interaction. Then, the nucleotides in the fluorous solvent could be back-extracted with aqueous ammonia in acetonitrile as non-fluorous solvent, and the extracts were directly injected to LC system. A hydrophilic interaction chromatography was utilized for separation of the nucleotides by gradient elution with the mixture of acetonitrile,water, and ammonium carbonate buffer (pH 10.0) as mobile phase, and an ultraviolet detection at 254 nm was used. The extraction recoveries of nucleotides were in the range from 70.4 to 96.8%. This method could be applied to the determination of nucleotides in cell samples.
Diabetes is one of the most common chronic diseases, and several new oral agents have been approved for type 2 diabetes management in recent years. A combination of different classes of antidiabetic agents is often required to avoid adverse effects such as severe hypoglycemia. A potential novel combination in development involves a fixed dose single-tablet combination of pioglitazone and a dipeptidyl peptidase 4 (DPP-4) inhibitor. DPP-4 inhibitors are a relatively new class of oral antidiabetic drugs. In this study, we simultaneously analyzed eight antidiabetic drugs, including newly developed DPP-4 inhibitors, by high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (HPLC–ESI–MS/MS). The developed method was applied to analyze the active ingredients in combination drugs and to determine the concentration of antidiabetic drugs in river water. Our results indicate that three recently approved antidiabetic drugs, sitagliptin, alogliptin, and vildagliptin, are present in river water.
Because of the structural similarity between long linear polyamine isomers, it is often very difficult to differentially quantify each hexaamine found in thermophilic bacteria. To quantify thermohexamine and homothermohexamine, for which separation has not been previously achieved, we analyzed a mixture of the heptafluorobutyryl derivatives of the two authentic hexaamines using gas chromatography-mass spectrometry (GC-MS). We found a correlation between the ratio of the hexaamines and the ratio of the intensities of two unique fragment ions in the MS spectra detected at m/z 774 in thermohexamine and m/z 1027 in homothermohexamine. The ratio of m/z (774/1027) vs. thermohexamine/homothermohexamine and m/z (1027/774) vs. homothermohexamine/thermohexamine calibration lines showed high linearity (r = 0.9997 and 0.9990, respectively) for hexaamine mixing ratios in the range of 0–2.33. These data indicate that the ratio of the hexaamines in a mixed solution can be determined by using the appropriate calibration line, depending on which hexaamine is present in greater quantity.
In this study, we report the physicochemical properties of three types of block copolymer micelles as measured by means of size exclusion chromatography coupled with multi-angle light scattering (SEC–MALS). Micelles were prepared from doxorubicin (Dox)-, Nile Red-, and 4-(N,N-dimethylsulfamoyl)-2,1,3-benzoxadiazole (DBD)-conjugated block copolymers. The molar mass and radius of gyration of the block copolymer micelles were measured, and the association number of the polymers was calculated from the measured molar mass. When the chemical structure of the block copolymers was varied (i.e., by varying the poly(ethylene glycol) chain length or by varying the polymerization degree of poly(aspartic acid)), the physicochemical properties of the resultant micelles differed markedly. The association number of the Dox-conjugated polymeric micelles was about 2.3 and 2.7 times as high as those of DBD- and Nile Red-conjugated polymeric micelles, respectively. The radius calculated from SEC–MALS was compared with that calculated from dynamic light scattering, and the ratio of the two radii provided information about the conformation of the resultant micelles.
Spherical polyimide particles have been synthesized as an extraction medium of volatile organic compounds (VOCs) in air samples. The polyimide was prepared with the starting materials of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (4,4'-oxydianiline, ODA), resulting spherical particles having an average diameter of about 5 µm. Packed into a laboratory made mini-extraction tube, the synthesized PMDA-ODA particles were employed as the adsorbent for the subsequent analysis in capillary gas chromatography. The extraction capacities for acetone, hexane, toluene are 0.42, 0.24, 0.78 µmol/g, respectively. The recoveries for these typical organic compounds are more than about 95%. The results clearly showed a good adsorption ability of the PMDA-ODA particles to typical VOCs frequently found in indoor environments, suggesting a future possibility to develop a more miniaturized sample preparation device specially-designed for on-site sampling of indoor air samples.