Pattern recognition of 8-hydroxy-2'-deoxyguanosine in biological fluids.

8-Hydroxy-2'-deoxyguanosine (8-OHdG), a product of oxidative DNA damage, which has been used as a sensitive and reliable marker of oxidative stress and carcinogenesis, is found in high levels in biological fluids of leukemia patients. A reliable screening method based on pattern recognition of 8-OHdG using stochastic sensors designed with graphene materials decorated with nanoparticles of TiO2Ag or TiO2Au was developed. 5,10,15,20-Tetraphenyl-21H,23H porphyrin (P), 2,6-bis((E)-2-(furan-2-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyridine (Py1), and 2,6-bis((E)-2-(thiophen-3-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyridine (Py2) were used as modifiers of the graphene paste in the design of sensors. The screening method used for pattern recognition was developed for two pH values accordingly with the nature of the biological fluid to be screened: pH = 3.02 for urine samples and pH = 7.49 for whole blood samples. High sensitivities and low limits of determination for 8-OHdG obtained at both pH values favored the early detection of leukemia. Recoveries over 98.00% with RSD (%) values lower than 1.00% proved the reliability of the proposed screening method. Graphical abstract Graphene based sensors detect 8-hydroxy-2'-deoxyguanosine in biological fluids.

Flow-injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter. A review.

Dopamine (DA) is one of the most important catecholamine neurotransmitters in the human central nervous system in the brain and plays a key role in the functioning of the renal, hormonal, and cardiovascular systems. Abnormal levels of dopamine are related to neurological disorders, such as schizophrenia and Parkinson's disease and the control and fluctuations of the amount of dopamine are extremely important in monitoring with analytical systems in the human brain. This review covers the attributes of flow-injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter and points out the advantages and disadvantages in the implementation thereof.

Application of porphyrins in flow-injection analysis: a review.

Porphyrins and metalloporphyrins fulfil a very important role in the metabolism of living organisms through biological pigments or biochromes and are therefore also employed in numerous applications in analytical chemistry. In flow-injection analysis the role of porphyrins and metalloporphyrins are centered as either that of analyte or that of a reagent or modifier in the determination of other species. This paper covers the attributes of porphyrin and metallophorphyrin complexes as enhancements in chemical analysis in flow-injection systems and points out the advantages and disadvantages in the implementation thereof.

Macrocyclic antibiotics as chiral selectors in the design of enantioselective, potentiometric membrane electrodes for the determination of S-flurbiprofen.

Construction of three novel enantioselective, potentiometric membrane electrodes based on carbon paste impregnated with different macrocyclic antibiotics vancomycin and teicoplanin as chiral selectors are described. The solutions for the construction of electrodes were prepared in phosphate buffer pH 4 for the vancomycin-based electrode (VCM), pH 6 and pH 6/40% acetonitrile solutions for teicoplanin-based electrodes, TCP I and II, respectively. The proposed electrodes were applied in the assay of S-flurbiprofen raw material and its pharmaceutical formulation by use of direct potentiometry, VCM electrode exhibiting the best enantioselectivity. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper.

Simultaneous detection of creatine and creatinine using a sequential injection analysis/biosensor system.

Carbon paste based biosensors for the determination of creatine and creatinine have been integrated into a sequential injection system. Applying the multi-enzyme sequence of creatininase (CA), and/or creatinase (CI) and sarcosine oxidase (SO), hydrogen peroxide has been detected amperometrically. The linear concentration ranges are of pmol/L to nmol/L magnitude, with very low limits of detection. The proposed SIA system can be utilized reliably for the on-line simultaneous detection of creatine and creatinine in pharmaceutical products, as well as in serum samples, with a rate of 34 samples per hour and RSD values better than 0.16% (n=10).

Determination of isoxsuprine hydrochloride by sequential injection visible spectrophotometry.

An automated sequential injection (SI) spectrophotometric method for the determination of isoxsuprine hydrochloride is described. The method is based on the condensation of aminoantipyrine with phenols (isoxsuprine hydrochloride) in the presence of an alkaline oxidizing agent (potassium hexacyanoferrate) to yield a pink colored product, the absorbance of which is monitored at 507 nm. Chemical as well as physical SI parameters that affect the signal response have been optimized in order to get better sensitivity, higher sampling rate and better reagent economy. Using the optimized aforesaid parameters, a linear relationship between the relative peak height and concentration was obtained in the range 1-60 mg l-1. The detection limit (as 3sigma value) was 0.3 mg l-1 and precision was 1.4% and 1.6% at 5 and 10 mg l-1, respectively. As compared to previous reports, wide linear range, low detection limit, and highly economical reagent consumption are the advantages of this automated method.

Sequential injection spectrophotometric determination of ritodrine hydrochloride using 4-aminoantipyrine.

A sequential injection spectrophotometric determination of ritodrine hydrochloride is described. The method is based on the condensation of aminoantipyrine with phenols in the presence of an alkaline oxidizing agent to yield a pink coloured product the absorbance of which is monitored at 503nm. Different sequential injection analysis (SIA) parameters including reagent concentrations have been optimised and used to obtain the analytical figures of merit. A linear concentration range of 3.1-123.5mumolL(-1) and a detection limit (as 3sigma-value) of 1.0mumolL(-1) were obtained. The precision was 2.4 and 2.3% relative standard deviation (R.S.D.) at 6.2 and 15.4mumolL(-1), respectively. This method is superior over previously reported ones in terms of linear range, short analysis time, high sample throughput, excellent reagent economy and minimum waste generation.

Sequential injection spectrophotometric determination of etilefrine hydrochloride.

A simple, fast, economical and automated sequential injection spectrophotometric method for the determination of etilefrine hydrochloride is developed. The method is based on the condensation reaction of etilefrine hydrochloride with 4-aminoantipyrine in the presence of alkaline potassium hexacyanoferrate and the absorbance of the colored product measured at 503 nm. Aspiration order, flow rate, reaction coil diameter, reaction coil length, concentration of 4-aminoantipyrine and potassium ferricyanide, as well as aspiration volume of reagents and sample has been optimized. Using these optimized parameters, a linear relationship between the relative peak height and concentration was obtained in the range 1-20 mg l(-1). The detection limit (as 3sigma value) was 0.1 mg l(-1) and precision was 2.7% and 1.5% at 1 and 2 mg l(-1), respectively. This method is superior over previously reported ones in terms of linear range, short analysis time, high sample throughput, excellent reagent economy and minimum waste generation.

New amperometric biosensors based on diamond paste for the assay of L- and D-pipecolic acids in serum samples.

Monocrystalline natural diamond, L-amino acid oxidase (L-AAOD), D-amino acid oxidase (D-AAOD), and paraffin oil were used for the design of the modified diamond paste. The technique used for the direct voltammetric assay was differential pulse voltammetry (DPV) with applied potential pulse amplitude of 25 mV vs. Ag/AgCl. Using the new amperometric biosensors L-pipecolic acid (L-PA) and D-pipecolic acid (D-PA) were determined reliably from serum samples at 700 and 200 mV vs. Ag/AgCl, respectively, with low limits of detection.

Utilization of maltodextrin based enantioselective, potentiometric membrane electrodes for the enantioselective assay of S-perindopril.

Enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with different maltodextrins {dextrose equivalent (DE) 4.0-7.0 (I), 13.0-17.0 (II) and 16.5-19.5 (III)} as chiral selectors for the assay of S-perindopril is described. The proposed electrodes could be reliably employed in the assay of S-perindopril raw material and from its pharmaceutical formulation, Coversyl((R)) tablets. The electrode based on maltodextrin (I) showed the best enantioselectivity and time-stability. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper.

Sequential injection spectrophotometric determination of phenylephrine hydrochloride in pharmaceutical preparations.

A fully automated sequential injection spectrophotometric method for the determination of phenylephrine hydrochloride in pharmaceutical preparations is reported. The method is based on the condensation reaction of the analyte with 4-aminoantipyrine in the presence of potassium ferricyanide. The absorbance of the condensation product was monitored at 503nm. A linear relationship between the relative peak height and concentration was obtained in the range 0.5-17.5mgl(-1). The detection limit (as 3sigma value) was 0.09mgl(-1) and repeatability was 0.8 and 0.6% at 2.5 and 5mgl(-1), respectively. Results obtained by this method agreed very well with those obtained by the AOAC official method.

Simultaneous determination of l-thyroxine (l-T(4)), d-thyroxine (d-T(4)), and l-triiodothyronine (l-T(3)) using a sensors/sequential injection analysis system.

Requirements of high purity and enantiopurity for the raw materials of active substances used for the pharmaceutical formulations involved utilization of high reliable analytical techniques for the analysis of the active compound. Sequential injection analysis system with electrochemical sensors as detectors proved to be a very good alternative for the chromatographic methods, as it is more reliable, not expensive, and faster. Drugs containing only l-thyroxine (l-T(4)) or both l-T(4) and l-triiodothyronine (l-T(3)) are formulated for the dysfunctions of thyroid. A sequential injection analysis system that can use two amperometric immunosensors (for the assay of l-T(3) and l-T(4)) and an amperometric biosensor (for the assay of d-thyroxine, d-T(4)) as detectors is proposed for the purity and enantiopurity tests of the raw materials used for the formulation of the drugs for thyroid. The system proved to be very reliable. The three compounds can be determined on-line in synthesis process control with a frequency of 20 samples per hour.

Spectrophotometric determination of magnesium in pharmaceutical preparations by cost-effective sequential injection analysis.

A simple and rapid, inexpensive spectrophotometric method was proposed for magnesium assay in pharmaceutical preparations by sequential injection analysis (SIA). The method is based on the reaction between o-cresolphthalein complexone (CPC) and Mg(II) in alkaline media, yielding a pink colored complex with absorption maximum at 570nm. Since the formation constant between Ca-CPC and Mg-CPC is similar, initially a sample/standard solution was aspirated into the holding coil followed by a mixture of masking-buffer solutions. This was done because masking of calcium should be accomplished before Mg-CPC complexation. Then the reagent was introduced into the reaction coil to produce a colored complex, which is measured spectrophotometrically at 570nm. In this way the interference of calcium was reduced. Furthermore, all the parameters that affect the reaction were evaluated. The calibration curve is linear over a range of 0-20mgl(-1) of Mg(II) with a detection limit of 0.24mgl(-1). A sample throughput of 80 samples per hour and relative standard deviation <2.0% were achieved. The proposed method was successfully applied for the assay of magnesium in three different compositions of pharmaceutical preparations (tablets). The results were found to be in good agreement with the manual flame atomic absorption spectrophotometry (FAAS) and UV-Vis spectrophotometry methods and with the claimed values by the manufactures. The t-test shows no significant difference at 95% confidence level.

Sequential injection spectrophotometric determination of iron as Fe(II) in multi-vitamin preparations using 1,10-phenanthroline as complexing agent.

A sequential injection analysis (SIA) system is proposed for the determination of iron (II). Fe(II) was determined by SIA based on the reaction between 1,10-phenanthroline and iron (II), yielding an orange-red colour complex with absorption maximum at 512nm. The method involved aspiration of 187mul sample/standard zone followed by a zone of a reagent solution containing 140mul of 7.8 x 10(-4)moll(-1) 1,10-phenanthroline into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil to a detector. The optimum condition was evaluated and the calibration curve is linear over a range of 0.25 to 5.0mgl(-1) of Fe(II) with detection limit of 18mugl(-1). A sample throughput of 40h(-1) was established. This technique is found to be simple, accurate, reproducible and sensitive. The proposed method was successfully applied for the determination of total iron as Fe(II) in pharmaceutical products (multi-vitamin tablets) and is especially useful for the determination of iron (II) in tablets with lower iron (II) contents. The results were found to be in good agreement with the results obtained by manual UV/Vis spectrophotometry and flame atomic absorption spectrometry (FAAS) and with claimed values by the manufacturers.

Sequential injection spectrophotometric determination of trace amounts of iodide by its catalytic effect on the 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction.

A simple and sensitive sequential injection spectrophotometric procedure is proposed for the determination of trace amounts of iodide in pharmaceutical preparations. The method is based on the catalytic effect of iodide on the (tetra base) 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction in acidic solution. The method involves a sequential aspiration of 255mul sample/standard followed by 170mul tetra base and then 128mul chloramine-T solutions into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil towards a detector. The resulting colored compound is measured at 600nm using an UV/Vis-spectrophotometer. All the parameters that affect the reaction were evaluated and the calibration curve is linear over a range of 0.1-6.0mugl(-1) of iodide concentration with detection limit of 0.05mugl(-1). A sample throughput of 80 samples per hour and relative standard deviation of less than 2.0% was achieved. The method is successfully applied for the determination of iodide in three different samples (tablets).

Simultaneous determination of L- and D-carnitine using a sequential injection analysis/amperometric biosensors system.

A sequential injection analysis (SIA) system is described for the simultaneous determination of L-and D-carnitine using amperometric biosensors as detectors. The SIA system was used, because of its high precision, accuracy and low sample and buffer consumption. The biosensors were designed using physical and chemical immobilization of L-amino acid oxidase and horseradish peroxidase (HRP) for the assay of L- carnitine, and D-amino acid oxidase and HRP for the assay of D-carnitine. The linear concentration ranges are in the pmol/l to nmol/l magnitude order, with very low limits of detection. The biosensors/SIA system was used reliably for on-line process control of the enantiopurity of carnitine with a frequency of 34 samples per hour.

Biosensors for the determination of ortho-acetyl-L-carnitine. Their utilization as detectors in a sequential injection analysis system.

In order to determine ortho-acetyl-L-carnitine, two biosensors were proposed. The biosensors were designed using physical immobilization of L-amino acid oxidase (L-AAOD) and horseradish peroxidase (HRP). Electrode characteristics were obtained and compared for the two carbon paste (graphite powder and paraffin oil) biosensors. The linear concentration ranges for the proposed biosensors were in the ranges of fmol/L to nmol/L, magnitude order with low limits of detection. Due to their reliability, the biosensors were used as detectors in a sequential injection analysis system, and gave reliable results for on-line assay of ortho-acetyl-L-carnitine in synthesis process control with a frequency of 75 samples per hour.

Determination of L- and D-enantiomers of methotrexate using amperometric biosensors.

In order to determine the enantiopurity of methotrexate (Mtx), seven biosensors were proposed for the assay of L-Mtx and three biosensors for the assay of D-Mtx. The biosensors were designed using physical and chemical immobilization of glutamate oxidase and/or L-amino acid oxidase (L-AAOD) and/or horseradish peroxidase (HRP) for the assay of L-methotherexate, and D-amino acid oxidase (D-AAOD) and HRP for the assay of D-Mtx. Electrode characteristics were obtained and compared for the different carbon paste based biosensors. The linear concentration ranges for the proposed biosensors were in the ranges of fmol l(-1) to pmol l(-1), magnitude order with limits of detection in the fmol l(-1) to nmol l(-1) concentration range. All biosensors were successful for the determination of the enantiopurity of Mtx as raw material, and in its pharmaceutical formulations (tablets and injections).

Simultaneous determination of creatine and creatinine using amperometric biosensors.

In order to determine creatine and creatinine amperometric biosensors were proposed. A bienzymatic biosensor based on creatinase (CI) and sarcosine oxidase (SO) was used for the assay of creatine and a trienzymatic biosensor based on CI, SO and creatininase (CA) for the assay of creatinine. The linear concentration ranges are of pmol l(-1) to nmol l(-1) magnitude order, with very low limits of detection. The biosensors proved high reliability for determination of creatine and creatinine as raw material, and in the pharmaceutical formulation.