The evaluation of short- and long-term stability studies for brimonidine in aqueous humor by DPV/BDDE method-possible application for direct assay in native samples.

A novel voltammetric method was developed for brimonidine (BRIM) determination in deproteinized aqueous humor, simplifying preparation of biological samples for analysis for stability studies. The differential pulse voltammetric (DPV) method using boron doped diamond electrode (BDDE), based on characteristic oxidation peaks, was proposed and successfully applied. The linearity range was within 5.0 × 10-6 to 5.0 × 10-5 M of brimonidine, and limit of detection and limit of quantitation were 1.94 × 10-6 M and 6.46 × 10-6 M, respectively. Intra-day and inter-day precision and accuracy were evaluated and all results were in accordance with validation ICH guidelines. The best short-term stability study results were obtained for a concentration level of 3.0 × 10-5 M expressed by deviation of + 1.86% between initial and post storage concentrations. A long-term stability study was performed for two concentrations of 3.0 × 10-5 M and 5.0 × 10-5 M and resulted in deviations of + 1.63% and + 3.56%, respectively. A freeze and thaw stability study indicated that samples might be frozen only once. The enhancement of DPV/BDDE method sensitivity gained by modification, for the analysis of immeasurable BRIM quantities in native, untreated aqueous humor, was reached for quantities of 6 or 12 nmol/0.1 mL aqueous humor with acceptable accuracy (up to + 7.5%). The nature of the process-the irreversible one electron oxidation voltammetric peak of BRIM-limited the sensitivity. Only electrochemical pre-treatment of the BDD electrode before each measurement significantly speeded up the whole procedure. The advantages of the proposed method are simplicity, short-time performance, and good specificity/selectivity, as well as satisfactory accuracy, and no chemical modification of BDDE was necessary.

An overview of the optical and electrochemical methods for detection of DNA - drug interactions.

A large number of inorganic and organic compounds is able to bind to DNA and form complexes. Among them, drugs are very important, especially chemotherapeutics. This paper presents the overview of DNA structural characteristics and types of interactions (covalent and non-covalent) between DNA molecule and drugs. Covalent binding of the drug is irreversible and leads to complete inhibition of DNA function, what conclusively, causes the cell death. On the other hand, non-covalent binding is reversible and based on the principle of molecular recognition. Special attention is given to elucidation of the specific sites in DNA molecule for drug binding. According to their structural characteristics, drugs that react non-covalently with DNA are mainly intercalators, but also minor and major groove binders. When the complex between drug and DNA is formed, both the drug molecule, as well as DNA, experienced some modifications. This paper presents the overview of the methods used for the study of the interactions between DNA and drugs with the aim of detection and explanation of the resulting changes. For this purpose many spectroscopic methods like UV/VIS, fluorescence, infrared and NMR, polarized light spectroscopies like circular and linear dichroism, and fluorescence anisotropy or resonance is used. The development of the electrochemical DNA biosensors has opened a wide perspective using particularly sensitive and selective electrochemical methods for the detection of specific DNA interactions. The presented results summarize literature data obtained by the mentioned methods. The results are used to confirm the DNA damage, to determine drug binding sites and sequence preference, as well as conformational changes due to drug-DNA interaction.

Application of adsorptive stripping voltammetry for determination of selected methoxyimino cephalosporins in urine samples.

In last two decades different electroanalytical methods are used for sensitive and selective determination of cephalosporins. In this paper the electrochemical behavior of methoxyimino cephalosporins, reduction mechanism and nature of the process at the mercury electrode surface is presented. Special attention is paid to the cephalosporins adsorption at the mercury surface. Based on this phenomenon, the adsorptive stripping methods are established for determination of low concentration of these drugs in urine samples, both in-vitro, and in-vivo conditions. The application of the adsorptive stripping differential pulse voltammetry (AdSDPV) for determination of cefpodoxime proksetile (CP), cefotaxime (CF), desacetylcefotaxime (DCF) and cefetamet (CEF) is summarized. The best sensitivity of determination in-vitro in urine was achieved for CP, in acid solutions (LOD 7.410(-9)M and LOQ 2.410(-8)M), followed by CF, CEF and DCF. This is in accordance with the strength of their adsorption. Determination of CF and DCF by AdSDPV in-vivo is also presented. Compared to other analytical methods, AdSDPV showed advantages in simplicity of the sample preparation, and over the other voltamperometric methods, higher sensitivity and selectivity.

The possibility of simultaneous voltammetric determination of desloratadine and 3-hydroxydesloratadine.

The electrochemical behaviour of desloratadine (DLOR) and its derivative 3-hydroxydesloratadine (3OH-DLOR) was investigated by direct current (DCP) polarography, cyclic (CV), differential pulse (DPV) and square-wave (SWV) voltammetry in Britton-Robinson (BR) buffer solutions (pH 4-11). Both compounds are reduced at mercury electrode in irreversible two electron reduction of the C=N bond of the pyridine ring in their molecules. The difference in their electrochemical behaviour was investigated, and the most pronounced distinction is observed at pH > 9, as a consequence of the deprotonation of the phenolic moiety in 3OH-DLOR molecule, yielding significant change in their reduction potentials (Ep DLOR = -1.48 V, and Ep 3OH-DLOR = -1.6 V). The observed results correlate with calculated LUMO energy levels and Hammet substituent constants (σ). Based on the difference in the reduction potential for DLOR and 3OH-DLOR, conditions for simultaneous determination these two molecules in alkaline medium were established. The best selectivity was achieved using SWV method at pH 10. The linearity of the calibration graphs were achieved in the concentration range from 1.5 × 10-6 M - 1 × 10-5 M for DLOR and 7.5 × 10-6 M - 5 × 10-5 M for 3OH-DLOR with detection limits of 2.29 × 10-7 M and 2.08 × 10-6 M, and determination limits of 7.64 × 10-7 M and 6.94 × 10-6 M, for DLOR and 3OH-DLOR, respectively. The method was checked in human plasma sample. Good response was obtained with LOD and LOQ values of 4.63 × 10-7 M and 1.54 × 10-6 M, for DLOR and 2.39 × 10-6 M and 7.97 × 10-6 M, 3OH-DLOR, respectively.

Simultaneous determination of cefotaxime and desacetylcefotaxime in real urine sample using voltammetric and high-performance liquid chromatographic methods.

Two rapid, accurate and sensitive methods are developed and validated for the quantitative simultaneous determination of cefotaxime (CFX) and its active metabolite desacetylcefotaxime (DCFX) in urine. Based on the previous results which showed the four electron reduction of CFX at approximately -0.5 V, and the new findings that DCFX reduction occurred at more positive potential (-0.23 V), the new adsorptive stripping differential pulse voltammetric (AdSDPV) method was developed for determination of CFX in the presence of DCFX. Linear responses were observed over a wide concentration range (0.07-0.52 microg/ml for CFX and 0.22-1.3 microg/ml for DCFX) in urine. The second assay involves subsequent separation on a reversed-phase HPLC column, with ultraviolet detection at 262 nm. Retention times were 4.057 and 1.960 min for CFX and DCFX, respectively. Linear responses were observed over a wide range, 0.55-6.60 microg/ml for CFX and 1.10-11.00 microg/ml for DCFX, in urine. The statistical evaluation for both methods was examined by means of within-day repeatability (n=5) and day-to-day precision (n=3) and was found to be satisfactory with high accuracy and precision.

Adsorptive properties of cefpodoxime proxetil as a tool for a new method of its determination in urine.

It was found that the reduction of the cefpodoxime proxetil (CP) molecule is strongly influenced by the adsorption. The adsorptive properties of CP were investigated in order to achieve an increase sensitivity of its determination. Validated adsorptive stripping differential pulse voltammetry is applied for the determination of low concentration of CP at pH 3.5 and 9.0 where the best pronounced adsorption effects were observed. The linearity of the calibration curves were achieved from 1 x 10(-8) to 1 x 10(-7)M with limit of detection (LOD) of 6.3 x 10(-9) and 7.1 x 10(-9)M, and limit of quantification (LOQ) of 2.1 x 10(-8) and 2.3 x 10(-8)M, at pH 3.5 and 9.0, respectively. The proposed method was tested for CP determination in spiked urine samples, enabling determination of low concentrations of CP.

Adsorptive stripping voltammetric determination of cefetamet in human urine.

On the basis of previously established mechanism of cefetamet (CEF) reduction, two methods were suggested for CEF determination-differential pulse polarographic and differential pulse adsorptive stripping voltammetric method. Two pH values were chosen, 2.0 and 8.4, where the electrochemical process was defined as one four-electron and two two-electron processes, respectively. The methods were performed in Britton-Robinson (BR) buffer and the corresponding calibration graphs were constructed and statistical parameters were evaluated. Applying the AdSV method at pH 2.0 linearity was achieved from 2 x 10(-8) to 2 x 10(-7) M with limit detection and limit determination of 4 x 10(-9) and 1.4 x 10(-8) M, respectively. At pH 8.4, the linearity was obtained between 6 x 10(-8) and 6 x 10(-7) M, with limit detection and limit determination of 1.5 x 10(-8) and 5 x 10(-8) M, respectively. Since the AdSV method enabled lower concentrations of CEF to be determined, this method was tested for CEF determination in spiked urine samples, and DPP method was used as a comparative one.