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Simplified Measurement of Partition Coefficient by Means of
the Pretreatment Function in the Auto-sampler

Yusuke OSAKA, Keiko YAMABE, Yoshiaki MAEDA, Junichi MASUDA, Masatoshi TAKAHASHI and Yoshihiro HAYAKAWASHIMADZU CORPORATION, 1 Nishinokyo-kuwabaracho, Nakagyo-ku, Kyoto 604-8511, Japan Introduction
A partition coefficient is a parameter reflecting hydrophobicity of chemical regents and is commonly assessed as the characteristic factor which affects the bio-availability of the chemical compound in the pharmaceutical area. The parameter typically used is the partition coefficient of octanol versus water (POW), which is expressed in common logarithms of concentration ratio (LogPOW). However, since there are some technological consideration and requirement of experienced skills for the operation in the existing Fig. 3 Chromatogram of the Antipyrine (Left: water layer, Right: octanol layer) methods, it is to be desired that an automated methodology for determination of LogPow with high reliability and efficiency is developed. In this presentation, we demonstrate the applicability of the developed method for determination of partition coefficient by the automated injection from the water or octanol phase separately using the auto-sampler. The results indicate that the LogPow was correctly obtained with reliability and high throughput determination.
Fig. 4 Chromatogram of the Lidocaine (Left: water layer, Right: octanol layer) System configuration
The Shimadzu Nexera system constructed of an LC-30AD solvent delivery unit, a DGU- 20A5 degassing unit, a SIL-30AC auto-sampler equipped with the pretreatment functions, a CTO-30A temperature column oven and a SPD-M20A Photo Diode Array detector with a temperature-controlled flow cell. Data was collected and processed by a LabSolutions LC/GC chromatographic data system. Deep-well plates were used as sample vials.
Fig. 5 Chromatogram of the Carbamazepine (Left: water layer, Right: octanol layer) Analytical conditions
: Gemini 4.6 mmID x 30 mm, 3 µm (Phenomenex, Inc.) : A; Water / Acetonitrile / TFA = 95 / 5 / 0.05 (v/v/v) B; Water / Acetonitrile / TFA = 5 / 95 / 0.05 (v/v/v) : 2 % (0 - 2 min), 2% to 100% (2 min – 2.9 min), 100 % (2.9 - 4.2 min) Fig. 6 Chromatogram of the Desipramine (Left: water layer, Right: octanol layer) : 10 mM sample* (5 µL)+Octanol (400 µL) +Water (400 µL) in a well : *Antipyrine, Lidocaine, Carbamazepine, Desipramine, Bifonazole, Chlorpromazine, Propranolol and Trimethoprim Automated pretreatment function
Fig. 7 Chromatogram of the Bifonazol (Left: water layer, Right: octanol layer) SIL-30AC has a major two types of its pretreatment modes; one is a standardized mode and the other is a pretreatment program mode. In the standardized mode, simple dilution can be performed by just setting the dilution factor, “Reagent” and other a few parameters shown in Fig.1, whereas a detailed program including dilution can be programmed in the pretreatment program mode.
Fig. 8 Chromatogram of the Chlorpromazine (Left: water layer, Right: octanol layer) The optimized program consisting of 14 lines commands was utilized in order to perform the automated Fig.1 pretreatment setting (Dilution mode) determination of partition coefficient as details described in Fig. 2. In the 5th line in the table of Fig. 2, the needle depth was set, as the needle stroke, 49 mm for water layer and 37 mm for octanol layer. Air was dispensed from the needle in the water layer to prevent from contamination. In addition, the needle was rinsed using internal and external solvent before the pretreatment. Fig. 9 Chromatogram of the Propranolol (Left: water layer, Right: octanol layer) Rinsing the outside of the needle using the external Needle move to the sample well "rn" is a rack number defined in the batch sequence file.
"sn" is a sample number also defined in the batch Aspirating air.
Moving down the needle into water or octanol layer.
49 mm is a needle stroke for water layer (in the left figure).
Fig. 10 Chromatogram of the Trimethoprim (Left: water layer, Right: octanol layer) Discussion
"iv" is a injection volume defined in the batch sequence file.
"ss" is a sampling speed set in the method file.
Determined value of each LogPOW by the Rinsing the outside of the needle using the external developed method was found to be in good agreement with the description in authentic For example, the obtained LogPow of Bifonazole, Wash the measuring line by rinse solution 0 which is higher than any others among the compounds in the table, indicates its high Fig. 2 pretreatment settings (pretreatment program mode) lipophilicity as the reference described. While, the obtained LogPow of Antipyrine indicates its Experimental results
hydrophilicity that is in agreement with its high solubility in water described in the reference. In Octanol and water was mixed well prior to adding the target compound. The sample addition, carryover had not been observed in the solution was vortexed followed by a centrifugation at 5000 rpm in 3 min. All samples were analyzed in the water layer at first followed by the octanol layer. The obtained Conclusion
chromatograms of eight model compounds are shown in Fig. 3 to 10, respectively. These results indicate that the SIL-30AC with pretreatment function is a powerful tool for the The blank test was performed before and after each of the analyzed layer in order to automated determination of LogPOW without any requirement of experienced skills. check the carryover. The results of these blank test are shown as overlapped (red colored) on each chromatogram. Calculated LogPOW based on the obtained peak Acknowledgement
area of water or octanol layer are listed in Table. 1. We would like to thank Mr. Takahiro TAKEUCHI (TEIJIN PHARMA LIMITED) who gave us useful advices and discussions for this study.

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