Plastic membrane electrodes for the potentiometric determination of codeine in pharmaceutical preparations

Four PVC membrane electrode systems responsive to codeinium cation are described. These electrodes are based on the use of the ion-association complexes of the codeinium cation with tetraphenylborate and reineckate counter-anions as ion-exchange sites in a PVC matrix plasticized with dioctylphthalate and dibutylsebacate. The performance characteristics of these electrodes reveal fast, stable and near-Nernstian responses for codeine down to concentrations of 3.5–7.0 × 10^–5 M. Over the pH range 2.5–7, the electrodes are satisfactory for manual and flow injection determination of codeine in various pharmaceutical preparations. There is negligible interference from a number of inorganic and organic cations and some common drug excipients. In the direct determination of 30 g/ml -1.0 mg/ml codeine, the average recovery is 100.6% and the mean standard deviation is ± 0.8%. The results compare favorably with those obtained by the British Pharmacopoeia method.     

Organic analysis with a new Ag(+)-selective membrane electrode

A new Ag(+)-selective membrane electrode obtained by impregnating a graphite rod (attached to the end of a Teflon tube) with the silver(I) chelate of 1-(2',3',5'-tri-O-benzoyl-beta-D-ribofuranosyl)-4-thioxo-5-methylthio-6-azauracil dissolved in chloroform gives a stable and reproducible response to silver in the 10(-1)-10(-5)M range with a slope of 60 mV/decade. A new method for determination of some beta-chlorovinyl ketones is based on use of the electrode in potentiometric titration of the chloride displaced by tertiary amines from beta-chlorovinyl ketones in forming the corresponding quaternary ammonium salts.     

Determination of organic impurities in pharmaceutical preparations

Data reported in the literature on methods for the determination of organic impurities in pharmaceutical preparations are systematized; the characteristics and possibilities of the methods are compared.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 124–136. Original Russian Text Copyright © 2005 by Glazkov, Bochkareva, Revelskii.     

New liquid-membrane electrodes for direct determination of atropine in pharmaceutical preparations

Solutions of atropinium 5-nitrobarbiturate in n-octanol and atropinium picrolonate in p-nitrotoluene are used as novel liquid ion-exchangers in electrodes that respond to the atropine cation. The performance characteristics of the two electrodes are almost identical: the response is linear for 10(-5)-10(-2)M atropine with a slope of 56.5 +/- 1 mV/concentration decade. The static response times are 30-90 sec and the potential readings are stable over the pH range 3-8. There is negligible interference from a number of inorganic and organic cations, and some common excipients. In the direct determination of 1-200 mug/ml of atropine, the average recovery with both electrodes is 98% (mean standard deviation 1.7%). Atropine has been determined in some pharmaceutical preparations with an average recovery of 98% (standard deviation 1.9%), the results being in agreement with those obtained by standard methods.     

Determination of sulpha-drugs with ion-selective membrane electrodes

A liquid-membrane mercury(II)-sensitive electrode is used for determination of various sulpha drugs by addition of excess of mercuric nitrate and potentiometric back-titration of the surplus mercury(II) with EDTA. The performance of the electrode is compared with that of an Ag(2)S crystal-membrane electrode. Attempts to prepare a sulphamethoxazole-sensitive electrode failed.     

Silver(I)-selective membrane electrodes based on sulfur-containing podands

Some podands, acyclic polyethers, were utilized as membrane active components to prepare Ag(+)-selective polymeric membrane electrodes. The thiapodand-based electrodes exhibited considerable selectivity toward Ag(+) over other heavy metal ions including Cd(2+), Pb(2+), Cu(2+) and Hg(2+). Also, good selectivity over alkali and alkali earth metal ions were observed. Response slopes, pH effects, response time, and signal baseline return of the sensor systems were studied in static mode and/or in a flow-injection system. The Ag(+)-selectivity was explained by the soft-soft interaction of the Ag(+) ion with the sulfur donor atoms as well as the stacking interaction between aromatic end groups of the host molecule on complexation.     

Cs+ -selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs⁺-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs⁺ in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10⁻¹ to 10⁻⁵ M Cs⁺, a slope of 55.4 mV/decade, and a lower detection limit (log a_Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li⁺, Na⁺, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.     

New BF(-)(4) and ClO(-)(4)-selective membrane electrodes and their pharmaceutical applications

The construction and general performance characteristics of ion-selective membrane electrodes sensitive to BF(-)(4) and ClO(-)(4) anions, respectively, are described. All electrodes show near-Nernstian responses in the range 10(-2) -10(-5)M. The selectivity of the electrodes to a number of organic and inorganic anions are reported. The electrodes are useful in the potentiometric determination of a few pharmaceutical preparations. The method is simple, rapid and does not require prior sample pre-treatment.     

Determination of Diazepam and associated compounds in pharmaceutical preparations

A method for determining Diazepam and its associated compounds in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. The separation was carried out at 30?°C and 25 kV, using a 25 mM borate buffer (pH 9.6) and 35 mM sodium dodecylsulfate (SDS) water solution. Under these conditions the analysis was carried out within 12 min with acceptable limits of detection and quantification. The method has been applied for quantifying Diazepam in different commercial formulations when it is the active drug and when it is employed associated with other drugs (Nortriptyline, Pyridoxine hydrochloride and Sulpiride).     

Determination of ethamsylate in pharmaceutical preparations by irreversible biamperometry

A novel flow-injection irreversible biamperometric method is described for the determination of ethamsylate. The proposed method is based on the oxidation of ethamsylate at one platinum electrode and the reduction of permanganate at another to form an irreversible biamperometric detection system. Ethamsylate can be determined over the range 1.0×10⁻⁶-1.0×10⁻⁴ mol l⁻¹ with a sample measurement frequency of 180 samples h⁻¹. The detection limit for ethamsylate is 4.0×10⁻⁷ mol l⁻¹. The stability of the proposed method is shown by a RSD of 0.52% for 11 replicate determinations of 2.0×10⁻⁵ mol l⁻¹ ethamsylate. The proposed method was applied to the determination of ethamsylate in pharmaceutical preparations.     

Determination of streptomycin in pharmaceutical preparations by gas chromatography

The antibiotic streptomycin can be reliably quantitated in injectable pharmaceuticals by GC. The manipulations are not difficult, and total analysis time for duplicate samples is less than twenty minutes. Reaction of the drug with aqueous sodium hydroxide solution generates maltol, which is extracted into chloroform prior to silylation. The silyl ether of maltol is then assayed, using naphthalene as internal standard. Duplicate analyses of twenty pharmaceutical samples showed a relative standard deviation of ±1.3%.     

Determination of levodopa in pharmaceutical preparations by irreversible biamperometry

Based on the electrocatalytic oxidation of levodopa at gold electrode and the reduction of permanganate at platinum electrode, a novel flow injection irreversible biamperometric method is developed for the determination of levodopa under the potential difference of 0 V imposed between two electrodes. In H2SO4 solution, the linear relationships between currents and the concentrations of levodopa are obtained in the range from 0.04 mg/L to 20 mg/L with the detection limit of 0.012 mg/L. The proposed method is applied to the determination of levodopa in pharmaceutical preparations.     

Determination of Diazepam and associated compounds in pharmaceutical preparations

A method for determining Diazepam and its associated compounds in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. The separation was carried out at 30 °C and 25 kV, using a 25 mM borate buffer (pH 9.6) and 35 mM sodium dodecylsulfate (SDS) water solution. Under these conditions the analysis was carried out within 12 min with acceptable limits of detection and quantification. The method has been applied for quantifying Diazepam in different commercial formulations when it is the active drug and when it is employed associated with other drugs (Nortriptyline, Pyridoxine hydrochloride and Sulpiride). Received: 30 October 1998 / Revised: 1 February 1999 / Accepted: 3 February 1999