Ibrahim H. Refaat

Antibacterial effect of various shapes of silver nanoparticles monitored by SERS

A comparative evaluation of antimicrobial effect of synthesized silver nanoparticles (AgNPs) of different shapes using different methods was performed. Spherical, triangular and hexagonal AgNPs with an average size of 40 nm were chemically prepared and characterized by transmission electron microscope (TEM) and UV-visible spectroscopy. The antimicrobial effect of these different AgNPs against the gram negative bacterium Escherichia coli (E. coli) was studied by surface enhanced Raman spectroscopy (SERS), the evaluation of growth curves and inhibition zones. SERS proved to be sensitive to monitor the changes that occurred in the bacterial cells upon interaction with AgNPs, which qualitatively compared well with the data provided by the reference methods. However, as SERS is already sensitive to initial changes in the chemistry of bacteria due to the antibacterial effect of the AgNPs, fast and detailed information is provided by SERS as opposed to the classical reference methods based on the evaluation of growth curves and inhibition zones. The results of this work also demonstrate that hexagonal AgNPs display the highest antibacterial effect when compared to other NPs shapes, with triangular AgNPs exhibiting no antibacterial effect under the adopted conditions.

Selective spectrophotometric determination of ascorbic acid in drugs and foods

A new analytical method was developed for the determination of ascorbic acid. The method is based on the reaction of ascorbic acid with 4-chloro-7-nitrobenzofurazane (NBD-Cl) in the presence of 0.2M sodium hydroxide, where a bluish green colour (lambda(max) 582 nm) is developed after dilution with 50% (v/v) aqueous acetone solution. Beers law was obeyed in a concentration range of 5-20 microg ascorbic acid/ml with a good correlation coefficient (r = 0.9990). The method was found to be highly specific for the determination of ascorbic acid in the presence of dehydro-ascorbic acid, all other vitamins and minerals possibly present in multivitamin preparations, rutin, salicylamide, acetyl salicylic acid, paracetamol, caffeine, phenylephrine hydrochloride and dipyrone. Moreover, the proposed procedure was also successfully applied for the determination of ascorbic acid in some canned and fresh fruit juices, some vegetables and infant milk products without interference from coloured and other substances present in the plant extracts.

Utility of surface enhanced Raman spectroscopy (SERS) for elucidation and simultaneous determination of some penicillins and penicilloic acid using hydroxylamine silver nanoparticles.

Elucidation and quantitative determination of some of commonly used penicillins (ampicillin, penicillin G and carbenicillin) in the presence of their main degradation product (penicilloic acid) were developed. Forced acidic and basic degradation processes were applied at different time intervals. The formed degradation products were elucidated and quantified using surface enhanced Raman spectroscopy (SERS). Silver nanoparticles (AgNPs) prepared by reduction of silver nitrate using hydroxylamine-HCl in alkaline medium were used as SERS substrate. The results obtained in SERS were confirmed by the application of LC/MS method. The concentration range was 100-600 ng/ml in case of the studied penicillins and 100-700 ng/ml in case of penicilloic acid. An excellent correlation coefficient was found in case of ampicillin (r=0.9993) and in the case of penicilloic acid (r=0.9997). Validation procedures were carried out including precision, robustness and accuracy by comparing F- and t-values of both the proposed and reported methods.

REVIEW ON RECENT SEPARATION METHODS FOR DETERMINATION OF SOME FLUOROQUINOLONES

Fluoroquinolones (FQs) are among the most important antibacterial agents (synthetic antibiotics) used in human and veterinary medicine. They are employed against all bacterial infections, particularly against urinary tract infections and acute respiratory diseases. In the last decade, there was no review covering all different analytical methods used for the determination of fluoroquinolone antibiotics. The present review presented recently published different electrophoretic and chromatographic methods for determination of seven fluoroquinolones (ciprofloxacin, gatifloxacin, levofloxacin, lomefloxacin, norfloxacin, ofloxacin, and sparfloxacin). Presented applications concern analysis of chosen fluoroquinolones in pure forms, different pharmaceutical formulations, biological fluids, and environmental samples.

Highly reproducible SERS detection in sequential injection analysis: Real time preparation and application of photo-reduced silver substrate in a moving flow-cell

This paper reports an improved way for performing highly reproducible surface enhanced Raman scattering of different analytes using an automated flow system. The method uses a confocal Raman microscope to prepare SERS active silver spots on the window of a flow cell by photo-reduction of silver nitrate in the presence of citrate. Placement of the flow cell on an automated x and y stages of the Raman microscope allows to prepare a fresh spot for every new measurement. This procedure thus efficiently avoids any carry over effects which might result from adsorption of the analyte on the SERS active material and enables highly reproducible SERS measurements. For reproducible liquid handling the used sequential injection analysis system as well as the Raman microscope was operated by the flexible LabVIEW based software ATLAS developed in our group. Quantitative aspects were investigated using Cu(PAR)2 as a model analyte. Concentration down to 5×10(-6) M provided clear SERS spectra, a linear concentration dependence of the SERS intensities at 1333 cm(-1) was obtained from 5×10(-5) to 1×10(-3) with a correlation coefficient r=0.999. The coefficient of variation of the method Vxo was found to be 5.6% and the calculated limit of detection 1.7×10(-5) M. The results demonstrate the potential of SERS spectroscopy to be used as a molecular specific detector in aqueous flow systems.

HPLC Determination of some antibilharzial antimonials by extraction of antimony.

The antimonial drug (antimony potassium tartrate, antimony piperazine tartrate or antimony lithium thiomaleate) in aqueous solution or biological fluid is treated with sodium diethyldithiocarbamate in the presence of a suitable masking reagent, the pH is adjusted to 9 +/- 0.5. and the antimony complex extracted with n-hexane and determined by reversed-phase HPLC with an ODS column and detection at 254 nm. The limits of detection are 20 ng (for antimony potassium tartrate and antimony lithium thiomaleate) and 16 ng (for antimony piperazine tartrate).

STABILITY INDICATING ASSAY AND KINETIC STUDY FOR NORFLOXACIN USING TLC-DENSITOMETRIC METHOD

A new, simple, and stability indicating thin layer chromatographic (TLC) method has been developed for estimation of norfloxacin. Study was performed on precoated silica gel F254 TLC plate using environmentally safe mobile phase consisting of n-butanol:methanol:ammonia (33%) (8:1:3.5 v/v). A Camag TLC Scanner 3 set at 282 nm was used for direct determination of the chromatograms in the reflectance/absorbance mode. Method was validated according to ICH guidelines. Determination coefficient of the calibration curve was 0.9962 in the range 6–150 ng/band with limit of detection and limit of quantification of 1.01 ng/band and 3.06 ng/band, respectively. Statistical comparison of the results with those of the official HPLC method showed good agreement between the official and the proposed methods with respect to accuracy and precision. Norfloxacin was subjected to forced degradation at 150°C with 2 M HCl or 2 M NaOH, and the degradation rate in both cases was studied. The calculated first order rate constant for the degradation were determined at 0.056 and 0.023 hour−1 and the t1/2 were 12.28 and 30.09 hr for acid and base degradation, respectively. The method has the potential to determine norfloxacin in different dosage forms and in quality control laboratories.

HPLC determination of niridazole

A high-performance liquid chromatographic method has been developed for the determination of niridazole in bulk form and in pharmaceutical dosage form. A reversed-phase system, based on an octadecylsilane-bonded stationary phase and a 60:40 v/v methanol/water mobile phase, is used. The detector response at 370 nm is linearly related to the amount injected, over a wide range. The method is sensitive, simple, rapid and precise.