Fluorimetric determination of mexiletine in serum by high-performance liquid chromatography using pre-column derivatization with fluorescamine

A simple, specific and sensitive micro-scale method for the assay of the antiarrhythmic agent mexiletine in human serum is described. The method uses high-performance liquid chromatography, with pre-column fluorimetric derivatization by fluorescamine. Following extraction with diethyl ether, mexiletine and 4-methylmexiletine (an internal standard) were derivatized with fluorescamine under weakly alkaline condition (pH 9.0) and chromatographed on a reversed-phase column with aqueous methanol-2-propanol as the mobile phase. The two fluorescent derivatives of mexiletine and the internal standard were separated as clear single peaks, and no interfering peaks were observed on the chromatograms. The detection limit for mexiletine was 0.005 micrograms/ml from only 100 microliters of serum, and the calibration curves in the range 0.01-5 micrograms/ml were linear, with an overall coefficient of variation of less than 5%. The analytical recovery of a known amount of mexiletine added to serum was almost 100%. This method proved to be effective in the rapid monitoring of the serum concentrations in patients who received this potent antiarrhythmic drug.     

Unreasonable postulate in the perturbative approach to quantum gravity

The conventional perturbative approach to quantum gravity is based on the expansion in powers of k, wherek denotes the Einstein gravitational constant. The introduction of a square root is due to the unreasonable postulate that thek0 limit of the gravitational field is ac-number. It is more natural that it is aq-number, which can be determined explicitly by the theory, and then the expansion becomes that in powers ofk but not of k. Thus the nonrenormalizability of Einstein gravity should be completely reconsidered in the light of the new expansion.     

Coating and water permeation properties of SiO2 thin films prepared by the sol-gel method on nylon-6 substrates

Nylon-6 substrates were coated with SiO₂ thin films by the sol-gel method and their water permeability coefficient was evaluated. Methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were used as starting materials. The addition of MTES to TEOS has enabled the formation of crack-free thin films on the substrates. The thin films strongly adhered to the substrates. The water permeability coefficients of nylon-6 substrates coated with these thin films decreased with the increase in the ratio of TEOS to the total alkoxides. The pretreatment of the nylon-6 substrates with -aminopropyltriethoxysilane was found to be effective to suppress the water permeability. The water permeability was suppressed by about 40% under the optimal condition.     

Nickel-catalyzed addition of P(O)-H bonds to propargyl alcohols: one-pot generation of phosphinoyl 1,3-butadienes

[reaction: see text] Diphenylphosphine oxide and related P(O)H compounds react with propargyl alcohols at room temperature in the presence of a catalytic amount of Ni(0) complex and Ph(2)P(O)OH to produce high yields of phosphinoyl 1,3-dienes though an efficient in situ dehydration process.