Micellar-enhanced synchronous-derivative fluorescence determination of derivatized folic acid in pharmaceutical preparations

Optical properties of folic acid in phosphate buffer solutions: the influence of pH and UV irradiation on the UV-VIS absorption spectra and photoluminescence

Using UV-VIS absorption spectroscopy, photoluminescence (PL) and photoluminescence excitation (PLE), the photodegradation reactions of folic acid (FA) in phosphate buffer (PB) solutions were studied. Regardless of the PB solution's pH, the UV-VIS spectra showed a gradual decrease in absorbance at 284 nm simultaneous with an increase in the absorbance of another band in the spectral range of 320-380 nm, which was downshifted under UV irradiation. The relative intensity of the FA PL band, situated in the spectral range 375-600 nm, was dependent on the pH of the PB solution. The FA PL intensity increased as increasing UV irradiation time up to 281 min. in PB solutions with pH values of 6.4 and 5.4. Under an emission wavelength of 500 nm, the position of the FA PLE spectrum changed as the PB solution pH varied from 7 to 5.4 and the irradiation time increased to 317 min. These changes were correlated with the formation of two photodegradation products, namely, pterine-6-carboxylic acid and p-amino-benzoyl-L-glutamic acid. According to UV-VIS spectroscopy and PL and PLE studies, the presence of various excipients in commercial pharmaceutical tablets does not affect the photodegradation of FA in PB solutions. Using IR spectroscopy, new evidences for the formation of the two photodegradation products of FA in PB solutions are shown.

Spectrofluorimetric and micelle-enhanced spectrofluorimetric methods for determination of Felodipine and Nimodipine in pharmaceutical preparations and human plasma

Rapid, simple and sensitive two spectrofluorimetric methods have been developed for determination of Felodipine (FLD) and Nimodipine (NDP). The first method is based on measuring the native fluorescence of either Felodipine or Nimodipine at 426 nm after excitation at 385 nm. The fluorescence intensity-concentration plots of Felodipine and Nimodipine were rectilinear over the concentration ranges (0.2-3.0) and (0.5-4.0) μg ml(-1), respectively. The second method is based on measuring the fluorescence intensity of the studied drugs in micellar media (0.3% Tween-80) at λex=385 nm and λem=423 nm. In the presence of 0.3% Tween-80, about 1.6-fold and 2.1-fold enhancement can be achieved in the relative fluorescence intensity (RFI) of Felodipine and Nimodipine, respectively. The fluorescence intensity-concentration plots of Felodipine and Nimodipine with Tween-80 were rectilinear over the concentration ranges (0.05-4.0) and (0.1-4.0) μg ml(-1), respectively with determination coefficients (r(2)) of 0.9981 and 0.9990, and limit of quantitation of 0.05 and 0.027μg ml(-1) for FLD and NDP, respectively. The proposed methods were validated according to ICH guidelines and have been successfully applied to the analysis of these drugs in their commercial tablets with high accuracy (97.6-98.8±0.50-1.42%, n=5). The high sensitivity of micellar method permits its application for determination of the cited drugs in spiked human plasma with % recovery (91.9-106.6±0.66-1.7%, n=6).

Novel method for determination of anthracene by coupling dispersive liquid-liquid extraction to first-derivative synchronous spectrofluorimetry

A novel method could be adopted successfully for determination of anthracene in environmental samples, utilizing dispersive liquid-liquid extraction followed by first-derivative synchronous fluorimetry at a constant wavelength difference Δλ = 165 nm, where a linear calibration curve was obtained in a concentration range of 0.5-100 ng mL(-1) at 244 nm. The detection limit was 0.1 ng mL(-1). The method can be easily adopted for determination of anthracene in aqueous media including tap water and river water. The recoveries obtained were 85.40-108.02%. The proposed method was validated according to International Conference of Harmonization (ICH) guide lines and successfully applied to determine anthracene in pure form and in water samples including real life water samples from different sources. All the results obtained were compared with those of published method, where no a significant difference was observed.

Chemiluminescence flow sensor for folic acid with immobilized reagents

A novel chemiluminescence (CL) sensor for folic acid combined flow-injection (FI) technology was presented in this paper. The analytical reagents involved in the CL reaction, including luminol and hexacyanoferrate(III), were both immobilized on an anion-exchange column in FI system. The CL signal produced by the reaction between luminol and hexacyanoferrate(III), which were eluted from the column through sodium phosphate injection, was decreased in the presence of folic acid. The CL emission was correlated with the folic acid concentration in the range from 0.01 to 15 microg ml(-1), and the detection limit was 3.5 ng ml(-1) folic acid (3sigma). At a flow rate of 2.0 ml min(-1), including sampling and washing, could be performed in 2 min with a relative standard deviation of < 2.5%. The flow sensor could be reused more than 300 times and has been applied to the analysis of folic acid in pharmaceutical preparations. and the recovery was from 97.4% to 100.4%.

Fluorimetric determination of procaine in pharmaceutical preparations based on its reaction with fluorescamine

A simple spectrofluorimetric analysis of a local anaesthetic named procaine using a specific labelling reagent for primary amino groups, has been developed. Because procaine shows very weak native fluorescence, the technique of spectrofluorimetry has been very much limited for its determination. A detail study of the variables affecting the derivatisation reaction (pH, fluorescamine (FC) concentration, temperature, reaction time), have minuciously been studied. The minimum detectable quantity is estimated as 7.7 ng ml(-1), with a relative standard deviation of 2.16% (ten determinations) for a procaine concentration of 100 ng ml(-1). The present method can be employed for the analysis of procaine by direct fluorescence measurements, without the interference from other compounds. The applicability of the present methodology have been demonstrated analysing three pharmaceutical preparations containing the analyte with satisfactory results.