Semi-micro liquid chromatography of aromatic amino acid metabolites using isocratic elution and column switching

The concentrations of catecholamine-related compounds in body fluids reflect sympathetic nerve functions. Measuring the enzyme activity of these metabolic pathways will improve diagnosis since a variety of symptoms are reported. An isocratic elution system with two column switching valves was developed using three types of semi-micro columns for fast chromatographic analysis of catecholamine related compounds. Columns are a pentyl-bonded phase, 50 x 2.1 mm i.d., a phenylhexyl-bonded phase, 100 x 2.1 mm i.d. and an octadecyl-bonded phase, 100 x 2.1 mm i.d. The separation of 20 standard compounds was achieved within 25 min using reversed-phase ion-pair liquid chromatography with an electrochemical detector. This new system was applied for analysis of catecholamine-related compounds in pig brain, since pigs are a widely used animal model for transgenic manipulation of neural genes, and MHPG (or VMA), DOPAC, DOPA, NE, EP, DA, 5HTP and 5HIAA were quantified.     

Retention behaviour of polyunsaturated fatty acid methyl esters on porous graphitic carbon

Retention with porous graphitic carbon was investigated with 25 structures of fatty acid methyl esters (FAMEs) with two different mobile phases: CH(3)CN:CHCl(3) 60:40 (v/v) and CH(3)OH:CHCl(3) 60:40 (v/v) with both 0.1% triethylamine (TEA) and an equimolar amount of HCOOH. Preliminary results showed that the use of TEA/HCOOH led to the response increase of saturated FAMEs with evaporative light scattering detection. No increase was observed for unsaturated one. These modifiers may slightly reduce the retention of FAMEs but did not significantly modify the separation factor with porous graphitic carbon. Thermodynamic parameters were calculated for each structure using Van't Hoff plot measured over the temperature range from 10 to 50 degrees C, with the both mobile phase conditions. All the studied compounds were found linked by the same retention mechanism on porous graphitic carbon. Quantitative in silico analysis of the retention using a molecular mechanics calculation demonstrated a good correlation between the retention factors and the molecular interaction energy values (r>0.93). Especially the Van der Waals energy was predominant, and the contribution of electrostatic energy was negligible for the quantitative analysis of the retention. The results indicate that Van der Waals force, hydrophobic interaction, is predominant for the retention of FAMEs on this packing material. The relative retention for highly unsaturated homologues can be changed by the selection of the weak solvent CH(3)CN or CH(3)OH. Then isomers differing only in the position of the carbon double bond on the alkyl chain can be separated and their behaviour is summarised as the closer the carbon double bonds to the FAME polar head, the more the retention decreases. Finally, the more important the number of carbon double bonds in the alkyl chain is, the smaller the retention is.     

Four new bisabolane-type sesquiterpenes from Ligularia lankongensis

The chemical constituents of the roots of two Ligularia lankongensis samples collected in Yunnan and Sichuan Provinces, China, were investigated, together with the DNA sequence of the atpB-rbcL and ITS regions. Four new highly oxygenated bisabolane-type sesquiterpenes (1 - 4) were obtained. Intraspecific diversity in the DNA sequence was found to be limited.     

Assessment of chemical elements in cosmetics' eyeshadows by X‐ray fluorescence and International Nomenclature of Cosmetic Ingredients characterization

Energy dispersive X‐ray fluorescence (EDXRF) technique, as a qualitative and quantitative analysis, was used for inorganic chemical elements determination (K, S, Cl, Al, Si, Ca, Ti, Mn, Fe, Pb, Zn, Rb, and Bi) in eyeshadows for safe human use. International Nomenclature of Cosmetic Ingredients standardized nomenclature was used for labels investigation to obtain data on legal regularity. Data of 23 samples were clustered by similarity, measuring relative concentrations of detected chemical elements. Calculating the correlation among such values, a similarity matrix was used to generate a dendrogram. Pb was found in samples silver color S12E and copper color S22I above permissible limits (20 μg/g). Same composition was reported for the pink (S01A), black (S02A), and brown (S03A) samples, but the same chemical elements were not detected by EDXRF in them. The best correlation was found between samples S08D and S23 J (0.961). The least correlation was 0.0012 between S01A and S12E. The clustering analysis showed 7 groups of similar samples according to EDXRF data. Relations among 6 eyeshadows' colors and chemical compositions were discovered by using decision trees, where the most determinant elements were Mn, S, Cl, Ca, and Fe, in this order. Commercial regularization and International Nomenclature of Cosmetic Ingredients standardization of eyeshadows in Brazil are not fully complied by the manufacturers of the investigated brands.     

Utilization of Sodium Nitroprusside as an Intestinal Permeation Enhancer for Lipophilic Drug Absorption Improvement in the Rat Proximal Intestine

As advanced synthetic technology has enabled drug candidate development with complex structure, resulting in low solubility and membrane permeability, the strategies to improve poorly absorbed drug bioavailability have attracted the attention of pharmaceutical companies. It has been demonstrated that nitric oxide (NO), a vital signaling molecule that plays an important role in various physiological systems, affects intestinal drug absorption. However, NO and its oxidants are directly toxic to the gastrointestinal tract, thereby limiting their potential clinical application as absorption enhancers. In this study, we show that sodium nitroprusside (SNP), an FDA-approved vasodilator, enhances the intestinal absorption of lipophilic drugs in the proximal parts of the small intestine in rats. The SNP pretreatment of the rat gastrointestinal sacs significantly increased griseofulvin and flurbiprofen permeation in the duodenum and jejunum but not in the ileum and colon. These SNP-related enhancement effects were attenuated by the co-pretreatment with dithiothreitol or c-PTIO, an NO scavenger. The permeation-enhancing effects were not observed in the case of antipyrine, theophylline, and propranolol in the duodenum and jejunum. Furthermore, the SNP treatment significantly increased acidic glycoprotein release from the mucosal layers specifically in the duodenum and jejunum but not in the ileum and colon. These results suggest that SNP increases lipophilic drug membrane permeability specifically in the proximal region of the small intestine through disruption of the mucosal layer.     

Analysis of urine by liquid chromatography in the ion-exchange or hydrophobic mode

The analysis of ultraviolet-absorbing constituents in urine was undertaken by anion-exchange and reversed-phase liquid chromatography. A newly developed anion exchanger (TSK-IEX540 DEAE) was used for ion-exchange mode liquid chromatography and its high polarity and physical strength greatly reduced the analysis time. Up to 80 peaks were resolved within 30 min. Hydrophobicity values were used to predict the retention times of acids in reversed-phase mode liquid chromatography.