PubMed Health⌕ Search

Biomedical subjects

M C Montenegro

Publications and source records attributed to M C Montenegro.

16 recordsLinked to original sources
PubMed2001

Detection of Epstein-Barr virus in tonsillar tissue of children and the relationship with recurrent tonsillitis.

Recurrent tonsillitis has been the subject of much investigation. Events considered to predispose to or cause recurrent tonsillitis (RT) include the misuse of antibiotic therapy in acute bouts, alterations in the microflora, structural changes in crypt epithelium and certain viral infections. Epstein-Barr Virus (EBV) infection usually occurs in early childhood and can persist in palatine tonsil lymphocytes to induce tonsillitis at a later date. We have examined the presence of EBV in palatine tonsils in order to assess the relationship between this virus and recurrent acute tonsillitis. Tonsils were obtained from 85 patients, 2--14 years old (mean 5.6 years old) who underwent tonsils and adenoid (T&A) removal because of recurrent tonsillitis (RT) or T&A hypertrophy (TH). Tissues specimens were processed for non-isotopic in situ hybridization (ISH) using EBER 1/2 oligonucleotides (EBER RNA). The indications for surgery were RT in 42 patients and TH in 43 patients. In 25 out of 85 cases (29.4%) a positive EBER RNA reaction (15 RT and 33 TH) was found. The chi(2)-test showed no statistically significant difference in frequency of positive results between RT and TH group. We conclude that tonsils of children can be colonized by EBV and that the virus may be implicated in RT and TH.

Adolescent↗
PubMed2001

Tetracycline-selective electrode for content determination and dissolution studies of pharmaceuticals by flow-injection analysis (FIA).

The present work describes the construction and evaluation of different tetracycline (TC)-selective electrodes without inner reference solution and with polymer membranes. The several electrodes were prepared with poly(vinyl chloride) or ethylene(vinyl acetate) membranes comprising o-nitrophenyl octyl ether or bis(2-ethylhexyl)sebacate as mediator solvents and tetracycline tetrakis(4-clorophenyl)borate as ion exchanger. The best performance was recorded for the poly(vinyl chloride) membranes with bis(2-ethylhexyl)sebacate. Using solutions with adjusted ionic strength, this type of electrode presented a slope of 57.4 mV decade(-1) and a reproducibility of +/-0.3 mV day(-1), for an analytical range from 1.2 x 10(-4) to 1.0 x 10(-2) M. The pH working range was 2.0-3.8. Tubular-shaped potentiometric detectors based on the same selective membrane were also constructed. When TC solutions with adjusted ionic strength of concentrations ranging from 1.0 x 10(-4) to 1.0 x 10(-2) M were injected into a single-channel flow manifold, the detectors presented a slope of 56.6 mV decade(-1) and a reproducibility of +/-0.5 mV day(-1). The pH working range was 1.9-3.9. Both batch and flow procedures were applied to the potentiometric analysis of oral dosage forms. Average recoveries were within 98.6 to 100.3% and the t test indicated the accuracy of these results in comparison to an independent methodology. The flow system with the potentiometric detector was employed in dissolution studies as well.

Electrodes↗
PubMed2001

Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products.

The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 x 10(-7) and 3.15 x 10(-6) M of sertraline with a limit of detection of 1.98 x 10(-7) M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples.

Antidepressive Agents↗
PubMed2001

Clavulanate-selective electrodes--application to pharmaceutical formulations.

The construction and assessment of a clavulanate anion-selective electrode and its application to the analysis of pharmaceutical formulations by direct potentiometry are described. The electrode, prepared without inner reference solution, was fabricated by use of a PVC membrane, with bis(triphenyl-phosphoranylidene)ammonium clavulanate as ion-exchanger dissolved in 2-nitrophenyl octyl ether as intermediate solvent and p-t-octylphenol as additive. The response of the electrode was linearly dependent on concentration within the range 2.4 x 10(-3)-1 x 10(-1) mol dm(-3) (ionic strength adjusted to 0.1 mol dm(-3)); the slope of the calibration plot was -59.4+/-0.9 mV decade(-1) and the reproducibility +/-0.6 mV day(-1). The response time was less than 20 s. Relative errors were <3.5% when results from analysis by direct potentiometry were compared with those from the reference method.

Anti-Bacterial Agents↗
PubMed2001

Potentiometric determination of acetylsalicylic acid by sequential injection analysis (SIA) using a tubular salicylate-selective electrode.

This paper deals with the development of an automated procedure for formulation assays and dissolution tests based on a sequential injection analysis (SIA) system involving an ion-selective electrode as sensing device. Construction of a tubular salicylate (Sal) selective electrode suitable for potentiometric determination of acetylsalicylic acid (Asa) in pharmaceutical formulations is described. The flow-through electrode is formed by a PVC membrane containing 29.2% (w/w) PVC, 5.8% (w/w) tetraoctylammonium salicylate (ionic sensor), 58.5% o-nitrophenyloctylether (plasticizer) and 6.5% (w/w) p-tert-octylphenol (stabilising additive which increases electrode selectivity). The calibration range is 0.05--10 mM Sal, the limit of detection (LOD) is 0.05 mM Sal, the slope is 56.0 mV per decade at 22 degrees C. The R.S.D. is 0.20% (15 readings) when determining 2.5 mM Sal in standard solution. The electrode is used for sensing Asa after its on-line chemical hydrolysis to Sal in a SIA system. The sampling rate is 6 h(-1) but for the dissolution tests the frequency is increased to 20 h(-1). The SIA set-up is employed for the assay of Asa in plain tablets, composed tablets and effervescent tablets and for performing dissolution tests of normal and sustained release tablets. Results obtained by this technique compare well with those required by the US Pharmacopoeia XXIV.

Aspirin↗
PubMed2001

Multi-task flow system for potentiometric analysis: its application to the determination of vitamin B6 in pharmaceuticals.

A flow set-up based on the sequential injection analysis concept was designed, aiming at increased automation and robustness of procedures related with potentiometric detection in pharmaceutical control. In this sense, programmable set-up calibration, ion-selective electrode characterization, standard addition techniques and titration procedures could be carried out without any stock solutions conventional handling or modification on the physical structure of the flow system. Evaluation of a flow-through vitamin B6 selective electrode and its application to routine analysis of pharmaceuticals were selected as models to demonstrate the system potentialities. The system ability to generate in-line calibrating solutions was verified by comparing the results with those obtained with solutions prepared by the manual procedure. The vitamin B6 determination in pharmaceutical products was carried out and in-line performed recoveries gave values within 97.4-103.5%. The system ability to perform titrations was ascertained using the precipitation reaction of vitamin B6 with tetraphenylborate. Other profitable features such as lower reagent consumption with a low effluent generation volume were also achieved.

Calibration↗
PubMed2001

Automatic multicommmutated flow system for diffusion studies of pharmaceuticals through artificial enteric membrane.

An automatic flow procedure with spectrophotometric detection was developed for the study of pharmaceuticals diffusion through an artificial enteric membrane. The manifold comprised two independent flow pathways, gathered by a diffusion unit with two compartments and an enteric lipophilic membrane. The pathways were automatically filled with solutions simulating digestive and plasmatic conditions by means of four solenoid valves. The diffusion of pharmaceuticals from the enteric to the plasmatic compartment was performed in closed loop pathways, and was continuously monitored by a flow cell coupled to the acceptor solution pathway. The volumes of the digestive and plasmatic solutions were 6.0 and 3.6 ml, respectively, which comprised filling unit compartment, pumping tubing and connecting flow lines. Pumping flow rates of donor and acceptor solutions were maintained at 6.0 and 2.5 ml min(-1), respectively. The proposed system was employed in diffusion studies of caffeine and aminophylline, and in the evaluation of the influence of tensioactive agents on the diffusion process. After continuous solutions circulation for 60 min, caffeine concentration in the acceptor stream was ca. 18% of its initial concentration at the digestive compartment. The system could be programmed to perform several replicates, stopping them with different degrees of diffusion without operator assistance. The data generated by the spectrophotometer was read by the microcomputer as a time function, and stored for further mathematical treatment.

Aminophylline↗
PubMed2000

Flow-injection analysis of dopamine in injections with a periodate-selective electrode.

Dopamine determination in pharmaceutical preparations based on its oxidation with periodate (IO(4)(-)) using a new IO(4)(-)-selective electrode under flow conditions is presented. An electrode with a tubular configuration, no internal reference solution, and a PVC (31. 2%) membrane, with metaperiodate bis(triphenylphosphoranylidene)ammonium (1.3%) as ion exchanger and 2-nitrophenyloctylether (67.5%) as mediator solvent, was used. Optimization procedures were directed at potentials versus dopamine readings instead of potential versus the remaining IO(4)(-). This approach was achieved by selecting a 50-cm reactor and an overall flow of 7 mL/min, and injecting 70 microL of dopamine standards in a 3.0 x 10(-4) M IO(4)(-) solution. Under these conditions, a linearity range of 8.0 x 10(-3) to 2.7 x 10(-1) g/L, with a slope of 310.1 +/- 7.4 mV L g(-1) and a reproducibility of +/-0.4 mV, were recorded (n = 8). Interference from common excipients was negligible. Under these conditions, analysis of dopamine injections (n = 12) presenting 200 mg/injection gave average and standard deviation values of 201.0 and 3.3 mg/injection, respectively. A simple and inexpensive flow-injection analysis (FIA) manifold, with a good potentiometric detector, enabled the analysis of 200 samples/h without requiring pretreatment procedures. Comparison with the dopamine injection analysis in the United States Pharmacopoeia monograph showed good accuracy, with a relative deviation of -0.2%.

Dopamine↗
PubMed1998

Cefuroxime selective electrodes for batch and FIA determinations in pharmaceutical preparations.

Different cefuroxime selective electrodes, without internal reference solution and comprising PVC membranes, were constructed and evaluated. Membranes were prepared with cefuroxime tetraoctylammonium (A) or cefuroxime bis(triphenylphosphoranylidene)ammonium (B) as ion-exchanger, 2-nitrophenyl octyl ether (X) or bis(2-ethylhexyl)sebacate (Y) as plasticizing mediator solvent and 4-tert-otcylphenol (TOP) as additive. From the comparative evaluation of the described electrodes, membranes comprising 2-nitrophenyl octyl ether, cefuroxime tetraoctylammonium and 4-tert-otcylphenol presented better working characteristics. For these electrodes (type XA-TOP), with a lifetime > 5 months, a lower limit of linear range of 2.8 x 10(-4) M, a practical detection limit of 1.3 x 10(-4) M, a reproducibility of approximately +/-0.6 mV day(-1) and a slope of -50.4 mV decade(-1), under H3PO4/NaH2PO4 solutions (pH 3.5; I =0.1 M), were found. The presence of the additive on the membranes was of crucial importance for the electrodes good characteristics. Interference from sulphate, chloride, nitrate, iodide, cefaclor, cefadroxil, cefazolin and cephradine, on the electrodes behaviour was evaluated. Only a slight interference from nitrate and iodide was recorded, being type XA-TOP electrodes the most selective units. Electrodes with a tubular configuration prepared with type XA-TOP membranes, aiming flow injection analysis, were also constructed. When these tubular potentiometric detectors were evaluated in a double-channel flow injection manifold, with 3.5 pH and 0.1 M ionic strength conditions, significantly better working characteristics than those of the corresponding conventional electrodes, namely higher slopes (-54.6 mV decade(-1)) and better reproducibilities (+/-0.2 mV day(-1)), were found. Both conventional and tubular type XA-TOP electrodes were used for injections analyses by batch and FIA, respectively, presenting low consumption of samples and reagents. Relative error deviations to the reference procedures <3.0% were found.

Cefuroxime↗
PubMed1997

Ion-selective electrodes for promethazine determinations in pharmaceutical preparations and application to flow injection analysis.

The construction and evaluation of PM-selective electrodes with a conventional configuration and without internal reference solution are described. Two different PVC membranes were prepared with PM tetraphenylborate dissolved in 2-nitrophenyl octyl ether (type A) or bis (2-ethylhexyl)sebacate (type B). When the electrodes were evaluated in 0.01 M ionic strength solutions, both presented linear responses from 5 x 10(-5) to 1 x 10(-2) M, slopes close to the theoretical value, practical detection limits of approximately 2 x 10(-5) M, reproducibilities of +/- 0.2 mV/day, and a quick response (< 20 s). Using phosphate buffer solutions (pH 6.0), type B electrodes presented a lower practical detection limit and a better reproducibility than type A. Selectivity against several cations was assessed by the separated solutions method, and the type B electrodes were generally more selective. The type B membrane was also used for the construction of tubular electrodes for the automatic analysis of pharmaceutical products by flow injection analysis (FIA). These tubular detectors, evaluated in a low dispersion FIA system, presented better selectivity and sensitivity than the corresponding conventional ones. Several pharmaceutical preparations were analyzed with both conventional and tubular electrodes. The results obtained by FIA presented relative deviations of < 2% when compared with those obtained from the United States Pharmacopoeia monographs.

Electrodes↗
PubMed1996

Construction and evaluation of PVC conventional and tubular tripelennamine-selective electrodes: their application in pharmaceutical preparations.

The construction and evaluation of tripelennamine conventionally-shaped ion-selective electrodes and tubular detectors for the determination of this compound in pharmaceutical formulations are described. Electrodes with conventional configuration have been constructed without an internal reference solution, using several types of immobilized ionic sensors in PVC. The different electrode membranes were prepared by using tripelennamine tetraphenylborate as ionic-exchanger, dissolved in 2-nitrophenyl octyl ether (type A), dibutylphthalate (type B) and bis-(2-ethylhexyl)sebacate (type C) as plasticizer solvents. The general working characteristics of the different types of conventional electrodes were evaluated in tripelennamine solutions, with adjusted ionic strength, showing a linear response in the concentration range of about 4 x 10(-5) - 1 x 10(-1) M and a slope near the theoretical value. The electrodes presented a fast response (> 20 s) and a high reproducibility (> or = 0.2 mV per day). The electrode selectivity in the presence of some interferents, such as sodium, potassium, lithium, ammonium, chlorpheniramine, diphenydramine, promethazine, meclizine and pentazocine, was good, particularly for those whose sensor membrane was prepared with tripelennamine tetraphenylborate dissolved in 2-nitrophenyl octyl ether (type A). Tubular detectors were also prepared using the same sensor membrane and were evaluated in a low-dispersion flow-injection manifold. Under these conditions the detectors presented response characteristics similar to those of the corresponding conventionally-shaped electrodes. The analysis of different pharmaceutical forms (creams, syrups and gels) gave good results with mean recoveries of 99.8-100.6% when the experiments were conducted by direct potentiometry and 99.9-100.4% where the same determinations were conducted by flow-injection analysis with tubular detectors.

Chemistry, Pharmaceutical↗
PubMed1996

Simultaneous assay of nitrite, nitrate and chloride in meat products by flow injection.

A flow injection (FI) analytical method for the simultaneous assay of nitrite, nitrate and chloride in meat products is reported. The method is based on the potentiometric determination of chloride using a tubular ISE and on the spectrophotometric determination of nitrite. The FI system consisted in splitting the flow after potentiometric detection using a tubular detector and the subsequent confluence of the flow before reaching the spectrophotometric detector. This allowed the reduction of nitrate to nitrite in part of the sample plug on an on-line copper cadmium reductor column. Since each channel had a different residence time, two peaks were obtained for nitrite and nitrite plus nitrate. Spectrophotometric determination was made after a diazotization-coupling reaction. The results obtained were in good agreement with reference procedures and showed adequate precision (RSDs less than 6% for chloride and nitrite and 2% for nitrate). A high sampling rate was obtained (120 determinations per hour corresponding to 40 samples per hour).

Chlorides↗
PubMed1995

FIA titrations of ephedrine in pharmaceutical formulations with a PVC tetraphenylborate tubular electrode.

A flow injection system for the titration of ephedrine in pharmaceutical products with potentiometric detection was developed. For this purpose a tetraphenylborate tubular electrode was constructed. The electrode was prepared without inner reference solution and with a PVC membrane based on tetrapentylammonium tetraphenylborate as ion exchanger and 2-nitrophenylphenyl ether as mediator solvent. Its operational characteristics were evaluated in a low dispersion manifold and compared with more conventionally shaped electrodes using the same sensor. In the pH range 2.5-11.5, the electrodes showed linear response between 3.8 x 10(-6) and 0.1 M with a slope of -56.4 mV/log[BPh4]. Ephedrine determinations in pharmaceutical products were carried out in a single channel manifold with a mixing chamber incorporated and using the tubular electrode as detector. Recovery rates of 98.6 +/- 2.5% were obtained in the analysis of tables, nasal drops and syrups with a sampling rate of about 60 h-1.

Electrodes↗
PubMed1994

Sequential flow-injection determination of ionic and total calcium in saliva.

In this paper a flow injection manifold for the sequential determination of ionic and total calcium in a small (75 microL) sample of saliva is presented. This setup incorporates two detectors, a tubular potentiometric detector and an atomic absorption spectrophotometer, for determining the ionic and total calcium, respectively. Furthermore, the saliva samples can be injected directly into the manifold without any pre-treatment or loss of carbon dioxide. The results of the analyses of 20 saliva samples were in good agreement with those obtained by the two reference procedures, the direct potentiometry for ionic calcium and atomic absorption spectroscopy for total calcium. The paired Student's t-test showed that there were no statistical differences in the results obtained. The relative standard deviations of ten consecutive measurements of the same salive sample were approximately 3% for ionic calcium and 4% for total calcium. Effects of differences in coexisting ions, ionic strength, and pH between standard solutions and samples were negligible.

Calcium↗
PubMedDate not supplied

PVC membrane electrode without inner reference solution for the direct determination of ephedrine in pharmaceutical preparations.

A PVC membrane electrode, without inner reference solution, based on an ion association extraction system responding to ephedrine is described. It incorporates an ephedrine-tetrakis (4-chlorophenyl)borate ion-pair complex in 2-nitrophenyloctyl ether. The prepared electrode exhibits a near Nernstian response (57.5 mV per decade) over the concentration range of 2 x 10(-5)-10(-1) M ephedrine in solutions of pH 2.5-9. The reproducibility of the electrode potentials were +/- 1 mV by day during at least 6 months. Response time was about 6 s for ephedrine concentrations between 10(-5) and 10(-1) M. Determinations of ephedrine in pharmaceutical preparations (tablets, nasal drops and syrups) by direct potentiometry gave an average recovery of 99.1% (w/w) and a mean standard deviation of 1.9% (w/w).

Chemistry, Pharmaceutical↗