A capillary GC-MS method for analysis of phenytoin and [C3]-phenytoin from plasma obtained from pulse dose pharmacokinetic studies

Stable isotope analogues of phenytoin are useful for pulse dose pharmacokinetic studies in epilepsy patients. A simultaneous assay was developed to quantitate phenytoin (5,5-diphenylhydantoin) and its stable isotope analogue [¹³C₃]-phenytoin (5,5-diphenyl-2,4,5-¹³C₃-hydantoin) from plasma. Quantitation was achieved by GC-MS analysis of liquid/liquid extracted plasma samples, with [²H₁₀]-phenytoin (5,5-di(pentadeuterophenyl)-hydantoin) as an internal standard. The total coefficients of variance (C.V._t) were <7% for phenytoin (2.5–40 μg ml⁻¹) and <10.3% for [¹³C₃]-phenytoin (0.1–6.0 μg ml⁻¹). The accuracy of the assay varied from 87.8–100.1% (phenytoin, 2.5–40 μg ml⁻¹) and 89.6–116.3% ([¹³C₃]-phenytoin, 0.02–6.0 μg ml⁻¹). The assay was tested under in vivo conditions by administration of a pulse dose of the stable isotope analogue to a single rat dosed to steady-state with fosphenytoin, a phenytoin prodrug. The results of the in vivo experiment demonstrate the usefulness of this assay for future pharmacokinetic studies in special population epilepsy patients.     

Simultaneous separation and determination of active components in Cordyceps sinensis and Cordyceps militarris by LC/ESI-MS

A simple and rapid isocratic LC/MS coupled with electrospray ionization (ESI) method for simultaneous separation and determination of adenine, hypoxanthine, adenosine and cordycepin in Cordyceps sinensis (Cs) and its substitutes was developed. 2-Chloroadenosine was used as internal standard for this assay. The optimum separation for these analytes was achieved using the mixture of water, methanol and formic acid (85:14:1, v/v/v) as a mobile phase and a 2.0×150 mm Shimadzu VP-ODS column. Selective ion monitoring (SIM) mode ([M+H]⁺ at m/z 136, 137, 268, 252 and 302) was used for quantitative analysis of above four active components. The regression equations were liner in the range of 1.4–140.0 μg ml⁻¹ for adenine, 0.6–117.5 μg ml⁻¹ for hypoxanthine, 0.5–128.5 μg ml⁻¹ for adenosine and 0.5–131.5 μg ml⁻¹ for cordycepin. The limits of quantitation (LOQ) and detection (LOD) were, respectively 1.4 and 0.5 μg ml⁻¹ for adenine, 0.6 and 0.2 μg ml⁻¹ for hypoxanthine, 0.5 and 0.1 μg ml⁻¹ for adenosine and cordycepin. The recoveries of four constituents were from 93.5 to 107.0%. The nucleoside contents of various types of natural Cs and its substitutes were determined and compared with this developed method.     

Spectrophotometric determination of pefloxacin in pharmaceutical preparations

It has been established that the antibiotic pefloxacin (Abaktal) methane-sulphonate 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 Job's, molar-ratio and Bent—French's methods, was pefloxacin: Fe(III) = 1:1 (pH = 2.50; λ = 360 nm; μ = 0.1 M). The relative stability constant, obtained by the methods of Sommer and Asmus was 10^5.02 (pH = 2.50; λ = 360 nm; μ = 0.1 M). The molar absorptivity of the complex at 360 nm was found to be 4.8 × 10³ l mol⁻¹ cm⁻¹, Beer's law was followed for pefloxacin concentrations of 2.15–85.88 μg ml⁻¹. The lower sensitivity limit of the method was 2.15 μg 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.     

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

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 × 10³ l mol⁻¹ cm⁻¹. Beer's 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.     

Bead injection spectroscopy-flow injection analysis (BIS-FIA): an interesting tool applicable to pharmaceutical analysis. Determination of promethazine and trifluoperazine

A bead injection spectroscopy-flow injection analysis (BIS-FIA) system for the spectrophotometric detection of promethazine and trifluoperazine is developed. The sensor is based in the oxidation of the phenothiazines by Fe(III) which is later determined by formation of the complex between Fe(II) and Ferrozine, [FeFz₃]⁴⁻. Immediately, this complex is retained on a homogeneous bead suspension of Sephadex QAE A-25 resin (500 μl) which has been injected previously in the system to fill a commercial flow-cell (Hellma 138-OS). The use of BI with respect to the use of a reusable flow-through sensor is justified because the complex is so strongly retained on the beads that the regeneration of the solid support becomes extraordinarily difficult in the proposed method. At the end of the analysis, beads are automatically discarded from the flow-cell, by reversing the flow, and transported out of the system. The analytical signals are measured at a wavelength of 567 nm, corresponding to the absorbance of the complex. Using a sample volume of 600 μl, the analytical signal showed a very good linearity in the range 0.5–8.0 μg ml⁻¹ and 0.5–10.0 μg ml⁻¹, with detection limits of 0.09 and 0.14 μg ml⁻¹ for promethazine and trifluoperazine, respectively. R.S.D.s (%) lower than 2% were obtained for both analytes. The proposed method is highly selective in the presence of other species that are normally encountered with these analytes. The sensor was satisfactorily applied to pharmaceutical preparations.     

Simultaneous LC determination of paracetamol and related compounds in pharmaceutical formulations using a carbon-based column

A simple, rapid and convenient high performance liquid chromatographic method, which permits the simultaneous determination of paracetamol, 4-aminophenol and 4-chloracetanilide in pharmaceutical preparation has been developed. The chromatographic separation was achieved on porous graphitized carbon (PGC) column using an isocratic mixture of 80/20 (v/v) acetonitrile/0.05 M potassium phosphate buffer (pH 5.5) and ultraviolet detection at 244 nm. Correlation coefficient for calibration curves in the ranges 1–50 μg ml⁻¹ for paracetamol and 5–40 μg ml⁻¹ for 4-aminophenol and 4-chloroacetanilide were >0.99. The sensitivity of detection is 0.1 μg ml⁻¹ for paracetamol and 0.5 μg ml⁻¹ for 4-aminophenol and 4-chloroacetanilide. The proposed liquid chromatographic method was successfully applied to the analysis of commercially available paracetamol dosage forms with recoveries of 98–103%. It is suggested that the proposed method should be used for routine quality control and dosage form assay of paracetamol in pharmaceutical preparations. The chromatographic behaviour of the three compounds was examined under variable mobile phase compositions and pH, the results revealed that selectivity was dependent on the organic solvent and pH used. The retention selectivity of these compounds on PGC was compared with those of octadecylsilica (ODS) packing materials in reversed phase liquid chromatography. The ODS column gave little separation for the degradation product (4-aminophenol) from paracetamol, whereas PGC column provides better separation in much shorter time.     

Determination of cisapride, its oxidation product, propyl and butyl parabens in pharmaceutical dosage form by reversed-phase liquid chromatography

A simple, rapid and reproducible high-performance liquid chromatography (HPLC) assay for cisapride, its oxidation product (OP), propyl and butyl parabens in a pharmaceutical formulation is described. Chromatography was performed at room temperature by pumping acetonitrile–20 mM phosphate buffer pH 7 (50:50, v/v) at 1.5 ml min⁻¹ through C₈ reversed-phase column. Cisapride, OP, propyl and butyl parabens were detected at 276 nm and were eluted at 9.7, 3.1, 5.1 and 7.1 min, respectively. Calibration plots were linear (r>0.999) for all compounds from 0.5 to 200 μg ml⁻¹ for cisapride and OP and 0.1–200 μg ml⁻¹ for propyl and butyl parabens. Detection limits for cisapride, OP, propyl and butyl parabens were 40, 46, 48 and 54 ng ml⁻¹, respectively. Forced degradation investigations showed that cisapride does not undergo degradation under heat, acidic and basic conditions but it was susceptible to oxidation. The proposed method was successfully applied to the assay of cisapride in the presence of preservatives and OP in a commercial suspension.     

Simultaneous determination of fosinopril and hydrochlorothiazide in pharmaceutical formulations by spectrophotometric methods

Three new spectrophotometric procedures for the simultaneous determination of fosinopril and hydrochlorothiazide are described. The first method, derivative-differential spectrophotometry, comprised of measurement of the difference absorptivities derivatized in the first-order (ΔD₁) of a tablet extract in 0.1 N NaOH relative to that of an equimolar solution in methanol at wavelengths of 227.6 and 276.4 nm, respectively. The second method, depends on the application ratio spectra derivative spectrophotometric method to resolve the interferance due to spectral overlapping. The analytical signals were measured at 237.9, 243.8 nm for fosinopril and 262.4, 269.3 and 278.6 nm for hydrochlorothiazide in the binary mixture, in the first derivative of the ratio spectra of the mixture solutions in methanol. Calibration graphs were established for 4.0–50.0 μg ml⁻¹ fosinopril and 2.0–14.0 μg ml⁻¹ hydrochlorothiazide in binary mixture. The third method, absorbance ratio method, the determination of fosinopril and hydrochlorothiazide was performed by using the absorbances read at 210.0, 219.5 and 271.7 nm in the zero-order spectra of their mixture. The developed methods were compared with absorbance ratio method. Application of the suggested procedures were successfully applied to the determination of this compound in synthetic mixtures and in pharmaceutical preparations, with high percentage of recovery, good accuracy and precision.     

Lobeline inhibits nicotine-evoked [H]dopamine overflow from rat striatal slices and nicotine-evoked Rb efflux from thalamic synaptosomes

The present study evaluated the interaction of lobeline with neuronal nicotinic acetylcholine receptors using two in vitro assays, [³H] overflow from [³H]dopamine ([³H]DA)-preloaded rat striatal slices and ⁸⁶Rb⁺ efflux from rat thalamic synaptosomes. To assess agonist interactions, the effect of lobeline was determined and compared to S(−)-nicotine. To assess antagonist interactions, the ability of lobeline to inhibit the effect of S(−)-nicotine was determined. Both S(−)-nicotine (0.1–1 μM) and lobeline (>1.0 μM) evoked [³H] overflow from superfused [³H]DA-preloaded striatal slices. However, lobeline-evoked [³H] overflow is mecamylamine-insensitive, indicating that this response is not mediated by nicotinic receptors. Moreover, at concentrations (<1.0 μM) which did not evoke [³H] overflow, lobeline inhibited S(−)-nicotine (0.1–10 μM)-evoked [³H] overflow, shifting the S(−)-nicotine concentration–response curve to the right. S(−)-Nicotine (30 nM–300 μM) increased (EC₅₀ VALUE=0.2 μM) ⁸⁶Rb⁺ efflux from thalamic synaptosomes. In contrast, lobeline (1 nM–10 μM) did not evoke ⁸⁶Rb⁺ efflux, and the lack of intrinsic activity indicates that lobeline is not an agonist at this nicotinic receptor subtype. Lobeline completely inhibited (IC₅₀ VALUE=0.7 μM) ⁸⁶Rb⁺ efflux evoked by 1 μM S(−)-nicotine, a concentration which maximally stimulated ⁸⁶Rb⁺ efflux. Thus, the results of these in vitro experiments demonstrate that lobeline inhibits the effects of S(−)-nicotine, and suggest that lobeline acts as a nicotinic receptor antagonist.     

Analysis of various nucleosides in plasma using solid phase extraction and high-performance liquid chromatography with UV detection

The National Cancer Institute (NCI) has screened many nucleosides for antiviral activity to the HIV-1 virus. Drugs demonstrating antiviral activity are tested in animal models to evaluate their toxicity and pharmacokinetic characteristics. These drugs are subsequently evaluated for efficacy in human clinical trials. Sensitive analytical methodology is needed to quantify nucleosides in plasma and other biological matrices in support of these studies. Battelle has modified and validated a reversed phase high-performance liquid chromatography (HPLC) method for several of these nucleosides that could be easily adapted for similar compounds. Methods have been validated for 6-chloro-2′,3′-dideoxyguanosine (6ClddG), 6-chloro-2′,3′-dideoxyinosine (6ClddI) and their primary metabolites 2′,3′-dideoxyguanosine (ddG) and 2′,3′-dideoxyinosine (ddI) in both rat and dog plasma containing EDTA. The method has also been validated for 2′-fluoro-2′,3′-dideoxyara-adenosine (βFlddA) and its primary metabolite 2′-β-fluorodideoxyinosine (βFddI) in rat plasma containing heparin. Calibration plasma standards were prepared over ranges of 0.1–10 μg ml⁻¹ for βFlddA and βFddI, 0.1–50 μg ml⁻¹ for 6ClddG and ddG, and 0.25–50 μg ml⁻¹ for 6ClddI and ddI in plasma containing 4 μg ml⁻¹ pentostatin. The addition of pentostatin to the plasma samples inhibits in-vitro deamination of the drug after collection. Quality control (QC) standards were prepared containing the appropriate anticoagulant and 4 μg ml⁻¹ pentostatin at concentrations within each of the bracketed calibration ranges in plasma. These methods have been successfully applied to plasma samples generated during various animal studies.     

Oxidation of adrenaline and noradrenaline by solved molecular oxygen in a FIA assembly

A simple and effective procedure is proposed for the study and simultaneous determination of adrenaline and noradrenaline. The fluorimetric determination of both substances is performed in a flow injection assembly and by oxidation of both drugs with the solved molecular oxygen. The influence of different parameters is empirically studied and the interpretation of the reaction mechanism is also added. The determination of adrenaline is monitored at 450 nm and the outputs at 520 nm correspond to the adrenaline and noradrenaline global amount; for both lectures λ_exc 329 nm. The influence of temperature is relevant and analytical determination occurred at 55 °C by immersing the sample loop in a water bath. The linear range for adrenaline is over 0.5–20 μg ml⁻¹, limit of detection for both compounds is 0.2 μg ml⁻¹: the influence of foreign compounds as potential interferents is also tested; and, finally the procedure is applied to determination of both chatecolamines in synthetic samples.     

Determination of meloxicam in bulk and pharmaceutical formulations

Three sensitive and reproducible methods for quantitative determination of meloxicam (mel) in pure form and in pharmaceutical formulations are presented. The first method is high performance liquid chromatography by which the drug is determined in the presence of its degradation products over concentration range 100–500 μg ml⁻¹ with mean percentage accuracy 100.13±0.53. The second method is based on measuring the absorbance of the formed neutral complex between basic methylene blue and mel in phosphate buffer (pH 8) at λ=653.5 nm over concentration range 1–5 μg ml⁻¹ with mean percentage accuracy 99.12±1.18. The third method is based on reaction between 2,3-dichloro-5,6-dicyano-p-benzoquinone resulting in the formation of an intense orange red coloured product after heating in a boiling water bath for 5 min. The coloured product exhibits an absorption maximum at 455 nm, over concentration range 40–160 μg ml⁻¹ with mean percentage accuracy 100.53±1.04.     

Simultaneous determination of valsartan and hydrochlorothiazide in tablets by first-derivative ultraviolet spectrophotometry and LC

First-derivative ultraviolet spectrophotometry and high-performance liquid chromatography (HPLC) were used to determine valsartan and hydrochlorothiazide simultaneously in combined pharmaceutical dosage forms. The derivative procedure was based on the linear relationship between the drug concentration and the first derivative amplitudes at 270.6 and 335 nm for valsartan and hydrochlorothiazide, respectively. The calibration graphs were linear in the range of 12.0–36.1 μg ml⁻¹ for valsartan and 4.0–12.1 μg ml⁻¹ for hydrochlorothiazide. Furthermore, a high- performance liquid chromatographic procedure with ultraviolet detection at 225 nm was developed for a comparison method. For the HPLC procedure, a reversed phase column with a mobile phase of 0.02 M phosphate buffer (pH 3.2)-acetonitrile (55: 45; v/v), was used to separate for valsartan and hydrochlorothiazide. The plot of peak area ratio of each drug to the internal standard versus the respective concentrations of valsartan and hydrochlorothiazide were found to be linear in the range of 0.06–1.8 and 0.07–0.5 μg ml⁻¹, respectively. The proposed methods were successfully applied to the determination of these drugs in laboratory-prepared mixtures and commercial tablets.     

Stability-indicating methods for the determination of sumatriptan succinate

Four stability-indicating methods were developed for the determination of sumatriptan succinate in the presence of its degradation products. The first method depends on the quantitative densitometric evaluation of thin-layer chromatography of sumatriptan succinate in the presence of its degradation products without any interference. Cyclohexane–dichloromethane–diethylamine (50:40:10 v/v/v) was used as a mobile phase and the chromatogram was scanned at 228 nm. This method determines sumatriptan succinate in the concentration range l–8 μg per spot with mean percentage recovery 100.52±1.23%. The second and third methods depend on the use of first-derivative (D₁) and second-derivative (D₂) spectrophotometry at 234 and 238 nm, respectively. These methods determine the drug in the concentration range 1.25–10 μg ml⁻¹ with mean percentage recovery 99.91±1.01% and 99.96±1.13% for (D₁) and (D₂), respectively. The fourth method depends on the use of ratio derivative spectrophotometric technique. The amplitude in the first derivative of the ratio spectra at 235 nm was selected to determine the cited drug in the presence of its degradation products. Calibration graph is linear in the concentration range 1.25–10 μg ml⁻¹ with mean percentage recovery 100.19±1.19%. The suggested methods were successfully applied for determining sumatriptan succinate in bulk powder, laboratory-prepared mixtures and pharmaceutical dosage forms (Imigran tablet) with good accuracy and precision. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by the reported method.     

Determination of some aminobenzoic acid derivatives: glafenine and metoclopramide

Simple, sensitive and accurate spectrophotometric methods for the determination of glafenine and metoclopramide hydrochloride are described. The first method is based on the oxidation of glafenine with iodic acid in strong acid medium to give a coloured diphenylbenzidine derivative and subsequent measurement of the coloured product at 509 nm. Beer's law is obeyed over the concentration range 2.5–20 μg ml⁻¹. The second method depends on the interaction of metoclopramide hydrochloride with p-dimethylaminocinnamaldehyde, to give a red coloured schiff's base with an absorbance maximum at 548 nm. Obedience to Beer's law is achieved over the concentration range 5–30 μg ml⁻¹. First-derivative method is used to overcome the slight interference of p-dimethylaminocinnamaldehyde reagent blank at the wavelength of measurement. Linearity between the peak heights at 576 nm versus concentration range 5–25 μg ml⁻¹ metoclopromide hydrochloride is obtained. The proposed methods have been successfully applied to the determination of these drugs in commercial products without interference. The validity of the methods is assessed by applying the standard addition technique, the relative standard deviation is less than 1%. The proposed methods are compared with reference methods with good agreement.     

Determination of benzalkonium chloride in contact lens solutions by positive-ion fast atom bombardment mass spectrometry

Under positive-ion fast atom bombardment (FAB) mass spectrometric conditions, benzalkonium chloride (BAK) afforded intense peaks at m/z 304 and 332, corresponding to the intact cations [M---Cl]⁺ of C₁₂ and C₁₄ homologues, respectively. The use of benzethonium chloride as an internal standard and thioglycerol as a FAB matrix allowed the direct and specific determination of the BAK content (0.004–0.020%) in commercial hard contact lens solutions through the individual assay of the two alkyl homologues. A linear relationship between the homologue concentration and the peak—area ratio was observed over the concentration range 3–180 μg ml⁻¹.     

Evaluation of micronucleus induction of sand dust storm fine particles (PM(2.5)) in human blood lymphocytes

Sand dust storms are common phenomena in the arid and semi-arid regions. Previous studies have demonstrated that the airborne air fine particulate matter (PM_2.5, particulates with an aerodynamic diameter ≤2.5 μm) and its extracts can induce human genetic damage of lymphocytes such as micronucleus formation, chromosomal aberration and so on. However, little is known about the health risks associated with sand dust storm PM_2.5 and its extracts. The aim of the present study is to investigate the micronucleus induction of sand dust storm PM_2.5 (include its organic and inorganic extract) from two different towns on human lymphocytes. The samples of normal PM_2.5 and sand dust storm PM_2.5 were collected in Wuwei (Gansu Province) and Baotou (Inner Mongolia), China. The cytochalasin-B cytokinesis-block test was employed and the cells were treated with 0, 33, 100, 300 μg ml⁻¹ sand dust storm PM_2.5 or normal ambient air PM_2.5 suspension (physiological saline as solvent control), or inorganic extract (0, 75, 150, 300 μg ml⁻¹, physiological saline as solvent control) or organic extract (0, 20, 40, 80 μg ml⁻¹, DMSO as solvent control) at the beginning of the cell culture. Both sand dust storm and normal PM_2.5 and their extract treatment cultures revealed an increase in the frequency of micronucleus. With the increase of treatment concentrations the frequency of micronucleus increased and the nuclear division index (NDI) values declined in a dose–response manner (P < 0.01). In the same concentrates, the frequency of micronucleus of normal ambient air PM_2.5 and its extract were significant higher than those of sand dust storm PM_2.5 (P < 0.01) except the treatment of Wuwei sample at higher doses, the treatment of inorganic extract of PM_2.5 at the highest dose (300 μg ml⁻¹) and the treatment of organic extract of PM_2.5 at the higher dose (40 and 80 μg ml⁻¹) either in Baotou or in Wuwei (P > 0.05). The toxicity of sand dust storm PM_2.5 and its extract at high dose is very potent. The frequency of micronucleus of normal PM_2.5 (include its organic extract) from Baotou were higher than those of Wuwei especially in low and middle dose (P < 0.05), but the treatment results of sand dust storm PM_2.5 (include its all extract) was not significantly different between the towns (P > 0.05).     

Spectrophotometric and atomic absorption spectrometric determination of certain cephalosporins

Two sensitive spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of certain cephalosporins (cefotaxime sodium and cefuroxime sodium). The spectrophotometric methods are based on the charge-transfer complex formation between these drugs as n-donors and 7,7,8,8-tetracyano-quinodimethane (TCNQ) or p-chloranilic acid (p-CA) as π-acceptors to give highly coloured complex species. The coloured products are measured spectrophotometrically at 838 and 529 nm for TCNQ and p-CA, respectively. Beer’s law is obeyed in a concentration range of 7.6–15.2 and 7.1–20.0 μg ml⁻¹ with TCNQ, 95.0-427.5 and 89.0-400.5 μg ml⁻¹ with p-CA for cefotaxime sodium and cefuroxime sodium, respectively. The atomic absorption spectrometric methods are based on the reaction of the above cited drugs after their alkali-hydrolysis with silver nitrate or lead acetate in neutral aqueous medium. The formed precipitates are quantitatively determined directly or indirectly through the silver or lead content of the precipitate formed or the residual unreacted metal in the filtrate by atomic absorption spectroscopy. The optimum conditions for hydrolysis and precipitation have been carefully studied. Beer’s law is obeyed in a concentration range of 1.9–11.4 and 1.78–8.90 μg ml⁻¹ with Ag(I), 14.2–57.0 and 13.3–53.4 μg ml⁻¹ with Pb(II) for cefotaxime sodium and cefuroxime sodium, respectively (for both direct and indirect procedures). The spectrophotometric and the atomic absorption spectrometric procedures hold well their accuracy and precision when applied to the analysis of cefotaxime sodium and cefuroxime sodium dosage forms.     

Selective kinetic determination of amikacin in serum using long-wavelength fluorimetry

A simple and rapid method for the determination of the antibiotic amikacin, involving the use of a long-wavelength fluorophor, namely indocyanine green, (ICG) is presented. The dye is oxidised by cerium(IV) in acidic medium, resulting in a sharp decrease of the fluorescence, but this fluorescence quenching is inhibited in the presence of amikacin, which can be ascribed to the formation of an ion pair between the fluorophor and the analyte. The initial rate of the system is monitored at λ_ex: 765 nm and λ_em: 812 nm as excitation and emission wavelengths, respectively, using the stopped-flow mixing technique, which makes the method applicable to automatic routine analysis. Each measurement is obtained in only 2–3 s. The method presents a detection limit of 0.02 μg m1⁻¹ in standard solutions, which corresponds to 2.5 μg ml⁻¹ in serum samples. The precision is in the range 4.8–6%. The good selectivity of the method allows amikacin to be determined in the presence of other antibiotics, including other aminoglycoside antibiotics, in serum. The recoveries obtained from the analysis of different samples were in the range 89.4–104.7%.     

Simultaneous determination of cinnarizine and domepiridone maleate from tablet dosage form by reverse phase ion pair high performance liquid chromatography

A new simple, precise, rapid and selective reverse phase ion pair high performance liquid chromatography (HPLC-RP) method has been developed for the simultaneous determination of cinnarizine (CINN) and domepiridone maleate (DOME) from tablets using acetonitrile–methanol–water–0.1 N sulfuric acid (37:10:48:5 v/v/v/v) containing sodium lauryl sulfate (0.01 M), as a mobile phase and a Machery Nagel nitrile column (10 μ, 25 cm×4.0 mm i.d.) as the stationary phase. The flow of mobile phase through the column was kept at 1.0 ml min⁻¹ through out the analysis. Detection was carried out using a UV detector at 225 nm. The retention times for CINN and DOME were 4.73 and 9.41 min, respectively. The linearity range and percentage recoveries for CINN and DOME were 4–1000 and 60–750 μg ml⁻¹ and 99.90 and 99.60%, respectively.