Milena Jelikic-Stankov

Fluorescence reaction and complexation equilibria between norfloxacin and aluminium (III) ion in chloride medium

Abstract Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid (NORH), reacts with aluminium(III) ion forming the strongly fluorescent complex [Al(HNOR)] 3+ , in slightly acidic medium. The complex shows maximum emission at 440 nm with excitation at 320 nm. The fluorescence intensity is enhanced upon addition of 0.5% sodium dodecylsulphate. Fluorescence properties of the Al-NOR complex were used for the direct determination of trace amounts of NOR in serum. The linear dependence of fluorescence intensity on NOR concentration, at a NOR to Al concentration ratio of 1:10, was found in the concentration range 0.001–2 μg/ml NOR with a detection limit of 0.1 ng/ml. The ability of aluminium (III) ion to form complexes with NOR was investigated by titrations in 0.1 M LiCl medium, using a glass electrode, at 298 K, in the concentration range: 2 × 10 −4 ≤ [ Al ] ≤ 8 × 10 −4 ; 5 × 10 −4 ≤ [ NOR ] ≤ 9 × 10 −4 mol/dm 3 ; 2.8 ≤ pH ≤ 8.3. The experimental data were explained by the following complexes and their respective stability constants, log ( β ± σ ): [ Al ( HNOR )], (14.60 ± 0.05); [Al(NOR)], (8.83 ± 0.08); [A1(OH) 3 (NOR)], (−14.9 ± 0.1), as well as several pure hydrolytic complexes of A1 3+ . The structure of the [Al(HNOR)] complex is discussed, with respect to its fluorescence properties.

Evaluation of matrix effect in determination of some bioflavonoids in food samples by LC–MS/MS method

In the present work the LC-MS/MS method with solid phase extraction for simultaneous determination of bioflavonoids rutin, quercetin, hesperidin, hesperetin and kaempferol in some food samples (red onion, orange peel and honey) was developed and the matrix effect accompanying this determination was quantified. The matrix effect evaluated using a postextraction addition method was found to be negative in the range -44 to -0.5%, indicating ionization suppression and strongly depended on bioflavonoid concentration. The observed matrix effect was explained taking into account the co-elution of phenolic acids, in terms of their acid-base and hydrophilic properties. The efficacy of extraction expressed as the absolute recoveries of flavonoids were 88-96%, indicating very good efficiency of extraction. The extracts of food samples obtained either by Soxhlet or ultrasonic extraction were analyzed for bioflavonoid content by the LC-MS/MS method in selected reaction monitoring mode using a triple quadrupole detector and standard addition method, which was found to be the most suitable calibration approach for these samples. The optimized separation was achieved on a Phenomenex Gemini C18 column with gradient elution and mobile phase composition A: 2% acetic acid in water and B: acetonitrile. R(s) values were in the range from 1.3 to 3.1, indicating good selectivity of the method. The obtained results (mg/100g fresh weight) for different bioflavonids were for rutin 0.16, for quercetin in the range 0.65-56, for hesperidin 0.016-24, for hesperetin 0.0068-36.4 and for kaempferol 0.14-1.63 and generally show good agreement with published data. Low detection limits (0.014-0.063 μg/mL) were obtained with acceptable recoveries (86-114%). Total time of analysis was less than 40 min, therefore the proposed method represents significant improvement over existing methods.

Study of solution equilibria between aluminum(III) ion and ofloxacin.

The complex formation equilibria between aluminium(III) ion and ofloxacin in 0.1 mol/l(-1) ionic medium at 298 K were studied by glass electrode pH-metric and UV spectrophotometric measurements. Within ofloxacin to aluminium mole ratio ranging from 2:1 to 25:1 and in pH interval from 2.5 to 10.5, the obtained experimental results were explained by the formation of the following complexes: AI(Hoflo) (log beta1,1,1 = 15.93 +/- 0.03), Al(oflo)2 (log beta1,2,0= 14.84 +/- 0.07), Al(oflo) (log beta1,1,0 = 10.20 +/- 0.04) as well as several other mixed and pure hydrolytic complexes. The structure and mechanism of the formation of the complexes and their possible implications on aluminum toxicity were discussed.

Spectrophotometric determination of pefloxacin in pharmaceutical preparations

It has been established that the antibiotic pefloxacin (Abaktal) methanesulphonate reacts with Fe(III) at pH 1.00-8.00 to form a water-soluble complex with maximum absorbance at 360 nm. The composition of the complex, determined spectrophotometrically by the application of Jobs, molar-ratio and Bent-Frenchs methods, was pefloxacin: Fe(III) = 1:1 (pH = 2.50; lambda = 360 nm; mu = 0.1 M). The relative stability constant, obtained by the methods of Sommer and Asmus was 10(5.02) (pH = 2.50; lambda = 360 nm; mu = 0.1 M). The molar absorptivity of the complex at 360 nm was found to be 4.8 x 10(3) l mol-1 cm-1. Beers law was followed for pefloxacin concentrations of 2.15-85.88 micrograms ml-1. The lower sensitivity limit of the method was 2.15 micrograms ml-1. The relative standard deviation (n = 10) was 0.57-1.07%. The method can be applied to the rapid and simple determination of pefloxacin in aqueous solutions and tablets.

Chemometric Optimization of a RP‐HPLC Method for the Simultaneous Analysis of Abacavir, Lamivudine, and Zidovudine in Tablets

Abstract A method has been developed and validated for the separation of abacavir, lamivudine, and zidovudine by high‐performance liquid chromatography (HPLC) on a C18 column with uv detection at 270 nm. The optimal conditions for separation were determined with the aid of a “critical resolution map” technique using the program DryLab®. The effect of simultaneously varying the pH and proportion of methanol in the mobile phase was studied to optimize the separation. A response surface diagram was used to study the interaction between factors determining the separation. The mobile phase composition that provides an optimal resolution of components in an acceptable elution time is water:methanol (60:40 v/v) + 0.2% TEA and pH = 3.20 (pH adjusted with H3PO4). A method is applied for the analysis of Trizivir® tablets (Glaxo Wellcome, UK). The powdered tablets were extracted with methanol:water (50:50 v/v) mixture and after addition of stavudine as an internal standard subjected to HPLC analysis and assayed by comparison of analyte to internal standard peak areas to concentration ratios.

High-performance liquid chromatographic assay of fleroxacin in human serum using fluorescence detection.

A HPLC method has been developed for the direct assay of fleroxacin in serum, without previous extraction. Serum samples, after the addition of sodium dodecylsulfate (0.5%), were injected directly into an LC Hisep column. The mobile phase consisted of acetonitrile, water and triethylamine in a per cent volume ratio 18:80:2. The pH of the mobile phase was adjusted to 6.50 with the addition of phosphoric acid. The drug was detected fluorometrically at lambda (ex )=280 nm and lambda (em )=450 nm . The linear concentration range of fleroxacin was between 0.01 and 2.0mg/l with a detection limit of 1ng/ml.

Spectrophotometric determination of oxytetracycline in pharmaceutical preparations using sodium molybdate as analytical reagent

Abstract A spectrophotometric method is proposed for the determination of oxytetracycline in pharmaceutical preparations. The method is based on the measurement of the absorbance of the molybdate—oxytetracycline complex at 404 nm (pH 5.50; μ = 0.1 M; 20°C). The composition of the complex (1:1) was determined by the application of the spectrophotometric methods of Job and Bent—French (pH 5.50; λ = 390 nm; μ = 0.1 M). The relative stability constant ( K ′ = 10 4.6 ) of the complex was obtained by the methods of Sommer and Nash (pH 5.50; λ = 390 nm; μ = 0.1 M; 20°C). The molar absorptivity of the complex was 9.5 × 10 3 l mol −1 cm −1 . Beers law was obeyed over the concentration range 2.48–34.78 μg ml −1 . The relative standard deviation RSD ( n = 10) was 0.27–0.39%. The method proposed can be applied to the assay of oxytetracycline in capsules. The detection limit of oxytetracycline is 2.5 μg ml −1 .

Investigation of molybdate(II)-rutin complex and the determination of the dissociation constant of rutin in water-ethanol mixture

Abstract By the application of the spectrophotometric methods the composition of the complex and by the pH-metric method the reaction of complex formation, were determined. It was found that a complex MoO3C27H26O16H2 2− was formed. The dissociation constant of rutin was determined pH-metrically at (20.0±0.1)[ddot]C (kd=8.64 × 10−15). The concentration stability constant of the complex was determined by Bent-French and Bjerrums methods, at various pH-values. Conditions are also given for the spectrophotometric determination of rutin by means of molybdate(II) as well as the accuracy of the method proposed. All Spectrophotometric measurements were done in 70% ethanol, at pH=6.30± 0.05 and ionic strength 0.015, whereas the determination of rutin was carried out in 50% ethanol, at pH=6.40±0.05, at room temperature (20[ddot]C) and the same ionic strength.

The Effect of Some Fluoroquinolone Family Members on Biospeciation of Copper(II), Nickel(II) and Zinc(II) Ions in Human Plasma

The speciation of Cu2+, Ni2+ and Zn2+ ions in the presence of the fluoroquinolones (FQs) moxifloxacin, ofloxacin, levofloxacin and ciprofloxacin, in human blood plasma was studied under physiological conditions by computer simulation. The speciation was calculated using an updated model of human blood plasma including over 6,000 species with the aid of the program Hyss2009. The identity and stability of metal-FQ complexes were determined by potentiometric (310 K, 0.15 mol/L NaCl), spectrophotometric, spectrofluorimetric, ESI-MS and 1H-NMR measurements. In the case of Cu2+ ion the concentration of main low molecular weight (LMW) plasma complex (Cu(Cis)His) is very slightly influenced by all examined FQs. FQs show much higher influence on main plasma Ni2+ and Zn2+ complexes: (Ni(His)2 and Zn(Cys)Cit, respectively. Levofloxacin exhibits the highest influence on the fraction of the main nickel complex, Ni(His)2, even at a concentration level of 3 × 10−5 mol/L. The same effect is seen on the main zinc complex, Zn(Cys)Cit. Calculated plasma mobilizing indexes indicate that ciprofloxacin possesses the highest mobilizing power from plasma proteins, toward copper ion, while levofloxacin is the most influential on nickel and zinc ions. The results obtained indicate that the drugs studied are safe in relation to mobilization of essential metal ions under physiological conditions. The observed effects were explained in terms of competitive equilibrium reactions between the FQs and the main LMW complexes of the metal ions.

Raman Spectroscopy as a New Biochemical Diagnostic Tool

Summary In this review, Raman spectroscopy is described as a new and potentially powerful diagnostic tool in comparison to routine biochemical tests. Advanced instrumentation and new Raman spectroscopy techniques enable rapid and simultaneous identification and/or determination of several biochemical parameters, such as glucose, acetone, creatinine, urea, lipid profile, uric acid, total protein, etc, with a very low limit of detection. Raman spectroscopy could also be applied in molecule and cell characterization, as well as diagnostics of atherosclerosis in its early stage. Raman spectroscopy is nondestructive and could be applied to all kinds of samples, which simplifies the diagnostics of numerous diseases and pathologic states. Special attention is paid to literature data illustrating the application of Raman spectroscopy for transdermal glucose monitoring and cancer diagnostics. Kratak sadržaj U ovom prikazu opisana je primena Ramanske spektrosko- pije kao nove metode velikih mogućnosti u dijagnostici, u poređenju sa rutinskim biohemijskim testovima. Metoda je razvijena i usavršena za identifikaciju i/ili određivanje velikog broja biohemijskih parametara, kao što su glukoza, aceton, kreatinin, urea, lipidni profil, mokraćna kiselina, ukupni proteini i drugi, uz veoma nizak limit detekcije. Ramanska spek- troskopija takođe se može primenjivati u molekulskoj i ćelij- skoj karakterizaciji, kao i za dijagnostiku ranog stadijuma ateroskleroze. Ramanska spektroskopija je nedestruktivna i može se primenjivati na sve vrste uzoraka, što pojednostavljuje dijagnostiku brojnih bolesti i patoloških stanja. Posebna pažnja u radu je posvećena podacima iz literature koji ilustru- ju primenu Ramanske spektroskopije u transdermalnom monitoringu glukoze i dijagnostici kancera