Search results for "Spectrophotometry"

Photometric Determination of the O2 Status of Human Blood Using the Oxystat System: cO2 (mL/dL), sO2 (%), cHb (g/dL)

1994

The O2 status of arterial human blood (Zander, 1990) can be completely described by a set of four parameters: cO2 (mL/dL), sO2 (%), cHb (g/dL) and pO2 (mm Hg).

Spectrophotometry: Pharmaceutical Applications

2013

Pharmaceutical analysis is mainly focussed in drug analyses, in raw materials and pharmaceutical formulations, involving the determination of active components, impurities, excipients, content uniformity, solubility, dissolution rate and stability.

Flow Methods in Pharmaceutical Analysis

2008

Reliability of the retention factor estimations in liquid chromatography.

2004

The retention factor is one of the most universally used parameters in chromatography. However, large differences in the experimental retention factor values are observed when the same compound is injected in a given stationary/mobile phase system under intermediate precision conditions. Conventional protocols for estimating retention factors have problems that mainly arise from difficulties in the hold-up time measurements and the omission of the existence of extra-column times by practicing chromatographers. In the present paper, three different approaches for estimating retention factors are tested: (i) classical retention factor estimations based on the gross hold-up time, (ii) based on…

Critical study of and improvements in chromatographic methods for the analysis of type B trichothecenes

2001

Various analytical methods used in the analysis of type B trichothecenes (deoxynivalenol, nivalenol, 3- and 15-acetyldeoxynivalenol) in cereals were compared and optimised in this work. These methods use either GC-electron-capture detection (ECD) of trimethylsilyl, trifluoroacetyl and heptafluorobutyryl derivatives or HPLC with UV or photodiode array detection of analytes. A new HPLC procedure using fluorescence detection prior derivatisation with coumarin-3-carbonyl chloride has been also tested. Five extraction solvents and two solid-phase extraction cartridges (silica, Florisil) plus a especial clean-up column (MycoSep 225) were compared in order to obtain the best recovery of the mycoto…

Sample preparation methods for the determination of pesticides in foods using CE-UV/MS.

2010

Much progress has been made in pesticide analysis over the past decade, during this time hyphenated techniques involving highly efficient separation with sensitive detection have become the techniques of choice. Among these, methods based on separation with mass spectrometric detection have resulted in greater likelihood of identification and are acknowledged to be extremely useful and authoritative methods for the determination of pesticide residues but the inherent advantages of the use of CE as a separation technique are well-known and can be summarized as high separation efficiency, low analysis time, high resolution power, and low consumption of samples and reagents. Although UV is the…

Stopped-flow Fourier-transform infra-red spectrometric speciation of glycolic and lactic acids in cosmetic formulations

2001

The dermatological activity of cosmetic formulations containing alpha-hydroxyacids depends on their different chemical forms, and it is therefore useful to determine these species in the finished products. In the present report a new procedure for studying the protonation equilibria of glycolic and lactic acids by stopped-flow Fourier-transform infra-red (FTIR) spectrometry is described. The procedure was validated for use in the speciation of glycolic and lactic acids in cosmetic formulations, with preferential attention given to glycolic acid, which is the most widely used. Species of these alpha-hydroxyacids can be approximately determined at different pHs and the total content of each a…

Spectrophotometric Determination of Hydralazine with 2-Hydroxy-1-naphthaldehyde in Pharmaceuticals

1991

Abstract A new extraction-spectrophotometric method for the determination of hydralazine, based on its reaction with 2-hydroxy-1-naphthaldehyde at 25 °C, is described. The calibration curve was linear between 0.4 and 6 mg/mL of hydralazine. The molar absorbtivity of the product at 408 nm is 40 900 L · mol − 1 · cm − 1 . The method described was applied to the analysis of hydralazine in pharmaceutical preparations containing reserpine, hydrochlorothiazide, bendrofluorthiazine, propranolol, and other substances. The agreement with the U.S.P. XXI method was satisfactory for tablets and injections, but not for pellets.

Evaluation of molecular mass and tacticity of polyvinyl alcohol by non-equilibrium capillary electrophoresis of equilibrium mixtures of a polymer and…

2011

Non-equilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) has been used to characterize polyvinyl alcohol (PVA). Commercial PVA samples with different molecular masses, from M(w)=15 up to 205 kDa, were used. According to the (13)C NMR spectra, the samples also differed in tacticity (stereoregularity). Mixtures of PVA and the anionic azo-dye Congo Red (CR) were injected in the presence of a borate buffer. The electropherograms gave a band and a peak due to the residual PVA-CR complex and the excess dye, respectively, plus a superimposed exponential decay due to the partial dissociation of the complex during migration. The stoichiometry of the PVA-CR complex, q=[monomer]/[dye…

Spectrophotometric Determination of the Antihistamines, Carbinoxamine Maleate and Doxylamine Succinate, in anN-Cetylpyridinium Chloride Micellar Medi…

1996

Abstract The pyridine antihistamines carbinoxamine maleate and doxylamine succinate were derivatized by hydrolysis with cyanogen bromide and coupling with aniline to form a polymethine dye, and determined by colorimetry. In a micellar cationic medium of N-cetylpyridinium chloride (NCPC), the reaction times were reduced and the sensitivities improved. In 0.1 M NCPC the apparent molar absorptivities of the derivatives were 5,900 and 3,500 M−1 cm−1, and the limits of detection (as 3s) were 8.6x10−7 M and 1.7x106 M, for carbinoxamine and doxylamine, respectively. The sensitivity was enhanced in a three- to six-fold factor with respect to a non-micellar medium. The reproducibility was 0.8% for 1…