Determination of Potassium Ferrocyanide in Foods by Resonance Rayleigh Scattering Method with Double-Charged Triaminotriphenylmethane Dyes

In pH 1.0 acidic medium, double-charged triaminotriphenylmethane dyes such as methyl green （MEG） and iodine green （IG） react with potassium ferrocyanide to form 2 ： 1 ion-association complexes by virtue of electrostatic forces and hydrophobic interaction. It results in the change of absorption and the great enhancement of resonance Rayleigh scattering （RRS） and the appearance of new RRS spectra. Two systems have similar spectral characteristics and their maximum RRS wavelengths are all located at 276 nm and smaller peaks are located at 332 and 457 nm, respectively. The intensity of RRS is directly proportional to the concentration of [Fe（CN）6]^4- in the range of 0.03-5.7 μg·mL^-1 （MeG system） or 0.04-5.9 μg·mL^-1 （IG system）. The RRS method has high sensitivity and the detection limit （3σ） for potassium ferrocyanide is 9.3 ng·mL^-1 （MeG system） or 11.2 ng·mL^-1 （IG system）. The optimum conditions, influencing factors and effects of foreign substances are investigated. The method also has a good selectivity. A sensitive, rapid and simple RRS method for the determination of potassium ferrocyanide in salinized food and table salt has been developed.     

Determination of verapamil hydrochloride with 12-tungstophosphoric acid by resonance Rayleigh scattering method coupled to flow injection system

A flow injection analysis (FIA) method coupled to resonance Rayleigh scattering (RRS) detection for the determination of verapamil hydrochloride (VP) was proposed. In pH 1.0 acidic medium, 12-tungstophosphoric acid (TP) reacted with VP to form an ion-association complex, which resulted in a significant enhancement of RRS intensity. The maximum scattering peak was located at 293 nm. RRS intensity was proportional to the concentration of VP in the range of 0.017-13.0 μg mL⁻¹, and the detection limit (3σ) was 5.1 ng mL⁻¹. The proposed method exhibited satisfactory reproducibility with a relative standard derivation (R.S.D.) of 2.1% for 11 successive determinations of 5.0 μg mL⁻¹ VP. Therefore, a novel method for the determination of VP by FIA-RRS was developed. The optimum reaction conditions and the parameters of the FIA operation such as flow rate, injection volume, reactor length, and so on had been optimized in this paper. The present method had been applied to the determination of VP in serum samples and pharmaceuticals with satisfactory results. The maximal sample throughput in the optimized system was 80 h⁻¹.     

Determination of Three Nonsteroidal Anti-Inflammatory Drugs in Human Plasma by LC Coupled with Chemiluminescence Detection

A simple and sensitive method was developed for the determination of three nonsteroidal anti-inflammatory drugs (NSAIDs)—ibuprofen, naproxen and fenbufen in human plasma. The method involved in column liquid chromatographic separation and chemilumenescence (CL) detection based on the CL reaction of NSAIDs, potassium permanganate (KMnO₄) and sodium sulfite (Na₂SO₃) in sulfuric acid (H₂SO₄) medium. The chromatographic separation was carried out using a reversed-phase C₁₈ column, which allowed the selective determination of the three medicines in the complicated samples. The special features of the CL detector provided lower LOD for determination than that of existing chromatographic alternatives. The results indicated that the linear ranges were 0.01–10.0 μg mL^?1 for ibuprofen, 0.001–1.0 μg mL^?1 for naproxen, and 0.01–10.0 μg mL^?1 for fenbufen. The limits of detection were 0.5 ng mL^?1 for ibuprofen, 0.05 ng mL^?1 for naproxen and 0.5 ng mL^?1 for fenbufen (S/N = 3). All average recoveries were in the range of 90.0–102.3%. Finally, the method had been satisfactorily applied for the determination of ibuprofen, naproxen and fenbufen in human plasma samples.     

HPLC and UPLC Methods for the Simultaneous Determination of Enalapril and Hydrochlorothiazide in Pharmaceutical Dosage Forms

High efficiency and less elution are the basic requirements of high-speed chromatographic separation. In this study, a new gradient reverse phase chromatographic methods were developed using HPLC and UPLC systems for simultaneous determination of enalapril maleate (ENL) and hydrochlorothiazide (HCZ) in pharmaceutical dosage forms. The chromatographic separations of ENL and HCZ were achieved on a Waters μ-Bondapak C 18, (300 × 3.9 mm, 10 μm) and Waters Acquity BEH C18 (100 × 2.1 mm, 1.7 μm) columns for HPLC within 5.30 min and UPLC within a short retention time of 1.95 min, respectively. A linear response was observed over the concentration range 0.270–399 μg mL^?1 of ENL, 0.260–399 μg mL^?1 of HCZ for HPLC system and 0.270–399 μg mL^?1 of ENL and 0.065–249 μg mL^?1 of HCZ for UPLC system. Also, limit of detection for ENL was 1.848 ng mL^?1 and 31.477 ng mL^?1 for HCZ, 2.804 ng mL^?1 for ENL and 2.943 ng mL^?1 for HCZ using HPLC and UPLC, respectively. The proposed methods were validated according to ICH guideline with respect to precision, accuracy, and linearity. Forced degradation studies were also performed for both compounds in bulk drug samples to demonstrate the specificity and stability indicating power of the HPLC method. Comparison of system performance with conventional HPLC was made with respect to analysis time, efficiency, and resolution.     

Development and Validation of an LC Method for Simultaneous Determination of Ascorbic Acid and Three Phenolic Acids in Sustained Release Tablets at Single Wavelength

A simple, rapid and sensitive column liquid chromatographic method was developed and validated to measure simultaneously the amount of ascorbic acid and phenolic acids at single wavelength (240 nm) in order to assess drug release profiles and drug-excipients compatibility studies for a new sustained release tablet formulation and its subsequent stability studies. A combined isocratic and linear gradient reversed-phase LC method was carried out at 240 nm. Quantification was achieved with reference to the external standards. The linearity for concentrations between 0.042 and 0.150 mg mL^?1 for ascorbic acid, 0.084–0.250 mg mL^?1 for chlorogenic acid, 0.053–0.360 mg mL^?1 for caffeic acid, and 0.016–0.250 mg mL^?1 for ferulic acid (r > 0.99 for all analytes) were established. The recovery of the active ingredients from the samples was at the range of 92.3–102.9%. Intra- and inter-day precisions were less than 2.5%. The limits of detection and quantification were 8 and 24 μg mL^?1 for ascorbic acid, 18 and 54 μg mL^?1 for chlorogenic acid, 37 and 112 μg mL^?1 for caffeic acid, and 11 and 34 μg mL^?1 for ferulic acid. The determination of the four active ingredients was not interfered by the excipients of the products. Samples were stable in the release mediums (37 °C) at least for 12 h.     

钯（II）-克林霉素-卤代荧光素体系的共振瑞丽散射光谱及其分析应用

在pH为5.0-5.4的乙酸-乙酸钠缓冲溶液中,克林霉素（Clin）与钯(Ⅱ)形成螯合阳离子,它能进一步与二碘荧光素（DIF）,赤藓红（Ery）,曙红Y（EY）等卤代荧光素类染料反应形成1：1：1的三元离子缔合物,此时将引起吸收光谱变化和荧光猝灭,同时还导致共振瑞利散射(RRS)的急剧增强并产生新的RRS光谱,钯(Ⅱ)-克林霉素与DIF,Ery和EY形成产物的最大散射波长分别位于285,287,32 1nm处,另外还有些较弱的散射峰存在。散射增强（ΔI）与克林霉素浓度在一定范围内成正比,可用于克林霉素的定量测定。对于DIF,Ery和EY体系的线性范围和检出限分别为0.025-2.1μg•mL-1和7.8 ng•mL-1,0.053-2.4μg•mL-1和16.0 ng•mL-1;以及0.038-2.4μg•mL-1和11.0 ng•mL-1。本文研究了适宜的反应条件,考察了共存物质的影响,表明方法有较好的选择性,基于三元离子缔合物的RRS光谱,发展了一种高灵敏、简便快速测定克林霉素的新方法。文中还对离子缔合物的组成,结构和反应机理,以及离子缔合物对吸收,荧光和RRS光谱的影响进行了讨论。     

Simultaneous Determination of Theobromine,Paraxanthine, Theophylline,and Caffeine in Urine by Reversed-Phase High-Performance Liquid Chromatography with Diode Array UV Detection

A reversed-phase high performance liquid chromatographic method was improved for the simultaneous determination of theobromine, paraxanthine, theophylline, and caffeine in urine. The method includes a liquid-liquid extraction at alkaline pH with ethylacetate. The 7-(2,3-dihidroxypropyl) theophylline was used as an internal standard (ISTD). The separation was achieved on a C₁₈ column using 14:86 methanol:buffer (25 mM KH₂PO₄ adjusted to pH 4 with ortho-phosphoric acid) solution as mobile phase under isocratic conditions at a flow rate 1 mL min^?1. An ultraviolet absorption at 274 nm was monitored. In these conditions, the LOD was 0.03 μg mL^?1 for theobromine, 0.02 μg mL^?1 for paraxanthine, 0.04 μg mL^?1 for theophylline, and 0.08 μg mL^?1 for caffeine. The method has been applied to urine samples.     

A Stability-Indicating Assay of Brimonidine Tartrate Ophthalmic Solution and Stress Testing Using HILIC

A stability-indicating hydrophilic interaction liquid chromatography (HILIC) method has been developed and validated for the quantitative determination of Brimonidine tartrate (BT) formulated as an ophthalmic solution. Isocratic separation was achieved using an acetonitrile-buffer mixture (92:8, v/v) at pH 7.1 on an unmodified silica column (250 × 4.6 mm, 5 μm). The drug was subjected to oxidative, hydrolytic, photolytic and thermal stress conditions and complete separation was achieved for the parent compound and degradation products. The influence of acetonitrile, pH and ionic strength of the buffer was studied. Linearity range and recoveries for BT were 100–400 μg mL^?1 and 100.12%, respectively. The method was validated for BT and indicated that the method was sufficiently sensitive with a limit of detection at 0.005 μg mL^?1 and a limit of quantitation at 0.02 μg mL^?1, respectively.     

Quantification of moxifloxacin in urine using surface-enhanced Raman spectroscopy (SERS) and multivariate curve resolution on a nanostructured gold surface

A simple procedure is proposed for the determination of the antibiotic moxifloxacin in urine using nanostructured gold as surface-enhanced Raman scattering signal enhancer. The standard addition method in conjunction to multivariate curve resolution-alternating least squares was applied to eliminate the matrix effect and to isolate the spectral contribution of the analyte. Even in the presence of unexpected interferences in the urinary media, it was possible to extract and quantify the analyte response, reaching, in this way, the so-called second-order advantage from first-order data. Moreover, although a saturation phenomenon of the metallic surface was observed, the results of the proposed methodology presented important advantages such as high sensitivity and simpler experimental procedures. The moxifloxacin was determined at levels of 0.70 and 1.50 μg mL^?1 in urine diluted to 1.0 % (corresponding to 70.0 and 150 μg mL^?1 in the original samples) with relative errors of 4.23 and 8.70 %, respectively. The limit of detection (0.085 μg mL^?1) and limit of quantification (0.26 μg mL^?1) values indicated that the quantification can be accomplished in urine up to 24 h after the administration of a single 400-mg dose.     

Analytical Application of Resonance Rayleigh Scattering,Frequency Doubling Scattering,and Second-Order Scattering Spectra for the Sodium Alginate-CTAB System

Three new methods for the determination of trace amounts of sodium alginate (SA) based on the reaction of SA with cetyltrimethylammonium bromide (CTAB) by resonance Rayleigh scattering (RRS), frequency doubling scattering (FDS), and second-order scattering (SOS) have been investigated. The SA can react with CTAB in a pH 10.0 Britton–Robinson buffer to form a new product, which can lead to a significant enhancement of RRS, FDS, and SOS intensities and appearance of new spectra. The maximum scattering wavelengths, λex/λem, appear at 351 nm/351 nm for RRS, 240 nm/480 nm for SOS, and 870 nm/435 nm for FDS, respectively. The increments of the scattering intensities (ΔI) are proportional to the concentration of SA in a certain range. The detection limits (3σ) for SA are 3.69 ng mL^?1 for the RRS method, 6.91 ng mL^?1 for the FDS method, and 7.45 ng mL^?1 for the SOS method under optimum conditions. The proposed methods were applied to the determination of SA in real samples with satisfactory results.     

UPLC-PDA Analysis for Simultaneous Quantification of Four Active Compounds in Crude and Processed Rhizome of Polygonum multiflorum Thunb

A novel, rapid and specific ultra performance liquid chromatography-photo diode array detection method was developed for the simultaneous determination of 2,3,5,4′-tetrahydroxystilbene-2-O-β-d-glucoside (TSG), emodin-8-O-β-d-glucoside (EMG), emodin (EM) and physcion (PS). The chromatographic separation was performed on an Acquity BEH C₁₈ column (100 × 2.1 mm i.d., 1.7 μm). The mobile phase was a mixture of 0.3% acetic acid–water and 0.3% acetic acid–acetonitrile employing gradient elution at the flow rate of 0.4 mL min^?1. The four compounds behaved linearly in the concentration range between 60.80–3040.00 μg mL^?1 (TSG), 0.50–25.00 μg mL^?1 (EMG), 2.16–108.00 μg mL^?1 (EM) and 1.56–78.00 μg mL^?1 (PS), respectively with correlation coefficients >0.999. The precision of the method were below 5% RSD. Recoveries of the four compounds ranged from 95.71 to 102.97%, with RSD values less than 2%.     

Improved Multianalyte Determination of the Intense Sweeteners Aspartame and Acesulfame‐K with a Solid Sensing Zone Implemented in an FIA Scheme

Abstract

A multianalyte flow‐through sensor is proposed for the simultaneous determination of aspartame (AS) and acesulfame‐K (AK) in tabletop sweeteners. The procedure is based on the transient retention of AK in the ion exchanger Sephadex DEAE A‐25 placed in the flow‐through cell of a monochannel flow injection analysis (FIA) set‐up using pH 2.70 ortophosphoric acid/sodium dihydrogen phosphate buffer 0.06 M as carrier. In these conditions AS is very weakly retained, which makes it possible to measure the intrinsic ultraviolet (UV) absorbance of first AS and then AK after desorption by the carrier itself. The applicable concentration range, the detection limit, and the relative standard deviation were the following: for AS, from 10 to 100 µg mL^?1; 5.65 µg mL^?1; 3.4% (at 50 µg mL^?1); and for AK, between 40 and 100 µg mL^?1; 11.9 µg mL^?1 and 1.61% (at 50 µg mL^?1). The method was applied and validated satisfactorily for the determination of AS and AK blends in tabletop sweeteners. The results were compared against an HPLC reference method.     

Simultaneous Determination of Ibuprofen and Diphenhydramine Citrate in Tablets by Validated LC

A stability-indicating LC method was developed for the simultaneous determination of ibuprofen and diphenhydramine citrate in pharmaceutical dosage forms. The chromatographic separation was achieved on an Inertsil ODS 3V, 150 × 4.6 mm, 5 μm, column. The mobile phase contained a mixture of 50 mM potassium dihydrogen phosphate buffer:acetonitrile:triethylamine:glacial acetic acid (55:45:0.2:0.2, v/v/v/v). This method allowed the determination of 2.85–9.14 mg mL^?1 of ibuprofen and 0.54–1.73 mg mL^?1 of diphenhydramine citrate, in a diluent consisting of pH 7.2, 50 mM potassium dihydrogen phosphate buffer:acetonitrile (40:60, v/v). The flow rate was 1.2 mL min^?1 and the detection wavelength was 260 nm. The limit of detection for ibuprofen and diphenhydramine citrate was 1.72 and 0.54 μg mL^?1 and the limit of quantification was 5.73 and 1.64 μg mL^?1, respectively. This method was validated for accuracy, precision and linearity. The method was also found to be stability indicating.     

Simultaneous Determination of Five Major Compounds in Polygonum cuspidatum by HPLC

An RP-HPLC method was developed for the first time to simultaneously determine five major compounds in Polygonum cuspidatum, namely resveratrol, polydatin, anthraglycoside B, emodin and physcion with UV detection at 306 nm. The column was an Agilent Zorbax SB-C₁₈ (250 × 4.6 mm i.d., 5 μm). The separation was carried out with a gradient program. The mobile phase was acetonitrile–water (containing 0.1% formic acid) at a flow rate of 1.0 mL min^?1. The standard curve was rectilinear in the range of 2.04–62.96 μg mL^?1 (r = 0.9998) for resveratrol, 20.13–239.7 μg mL^?1 (r = 0.9998) for polydatin, 7.19–71.92 μg mL^?1 (r = 1.0000) for anthraglycoside B, 2.68–83.68 μg mL^?1 (r = 0.9998) for emodin and 0.60–14.37 μg mL^?1 (r = 0.9997) for physcion. The recoveries of the markers were 96.0, 106.5, 97.8, 97.9 and 98.1%, respectively. The relative standard deviation of intra-day and inter-day were less than 5.0 and 2.3%. This method was simple, accurate and reproducible. The developed method was successfully applied to analyze five compounds in P. cuspidatum of 20 commercial brands.     

Simultaneous Determination of Clobetasol Propionate and Calcipotriol in a Novel Fixed Dose Emulgel Formulation by LC-UV

A new, rapid, selective, cheap and simple RP-LC method has been developed and validated for the simultaneous determination of clobetasol propionate and calcipotriol mixtures in bulk drugs (raw materials) and in a novel-fixed dose emulgel formulation. Separation was carried out using a NovaPak C18 column with methanol:water (74:26 v/v) as mobile phase for isocratic elution at a flow rate of 1.0 mL min^?1. The column temperature was set at 25 °C. Calibration curves were established ranging between 0.5 and 20 μg mL^?1 and 0.5 and 10 μg mL^?1 for clobetasol propionate and calcipotriol, respectively. Limit of detection and limit of quantification values of the method was found as 0.16 and 0.48 μg mL^?1 for clobetasol propionate and 0.10 and 0.30 μg mL^?1 for calcipotriol, respectively. The method was validated in accordance with ICH guidelines and obtained results proved that the proposed method was precise, accurate, selective and sensitive for the simultaneous analysis of clobetasol propionate and calcipotriol. The proposed method can be easily applied for the simultaneous determination of clobetasol propionate and calcipotriol in prepared emulgel formulations. The obtained validation results showed that the RP-LC method is suitable for routine quantification of clobetasol propionate and calcipotriol in emulgel formulations with high precision and accuracy.     

Determination of Sulfonamides in Pharmaceuticals and Rabbit Plasma by Microchip Electrophoresis with LED-IF Detection

In this paper, we describe a compact and low-cost light-emitting diode-induced fluorescence (LED-IF) detection coupled to microchip electrophoresis for the determination of sulfonamides in pharmaceutical formulations and rabbit plasma. Three fluorescein isothiocyanate-labeled sulfonamides in rabbit plasma were separated in the running buffer of 40 mM phosphate buffer (pH 7.0) at the separation voltage of 2.0 kV, and detected by LED-IF detector in which the high-power blue LED was driven at the constant current of 150 mA and the emitted fluorescence over 510 nm was collected by a planar photodiode. The linear concentration ranged from 2.0 to 125.0 μg mL^?1, both for sulfadiazine and sulfamethazine with the correlation coefficients (r ²) of 0.995 and 0.997, respectively, and from 2.0 to 100.0 μg mL^?1 with the correlation coefficients (r ²) of 0.997 for sulfaguanidine. The limits of detection for the three sulfonamides were 0.36–0.50 μg mL^?1 (S/N = 3). Intra-day and inter-day precision of migration time and peak area for the determination of sulfonamides were <4.5 %. This method has been successfully applied to the analysis of sulfonamides in pharmaceuticals, and could be used to study the pharmacokinetics of sulfonamides in rabbit.     

Ion-Pair LC Method for Simultaneous Determination of Aliskiren Hemifumarate,Amlodipine Besylate and Hydrochlorothiazide in Pharmaceuticals

A rapid and precise LC method was developed for the simultaneous determination of aliskiren hemifumarate (ALS), amlodipine besylate (AML) and hydrochlorothiazide (HCZ) using acetonitrile:25 mM octane sulfonic acid sodium salt monohydrate in water (60:40 v/v) as the mobile phase. The flow rate was maintained at 1.2 mL min^?1 on a stationary phase composed of Supelco, Discovery^® HS (C18) column (25 cm × 4.6 mm, 5 μm). Isocratic elution was applied throughout the analysis. Detection was carried out at λ _max (232 nm) at ambient temperature. The method was validated according to ICH guidelines. Linearity, accuracy and precision were satisfactory over the concentration ranges of 32–320, 2–44 and 4–64 μg mL^?1 for ALS, AML and HCZ, respectively. LOD and LOQ were estimated and found to be 0.855 and 2.951 μg mL^?1, respectively, for ALS, 0.061 and 0.202 μg mL^?1, respectively, for AML as well as 0.052 and 0.174 μg mL^?1, respectively, for HCZ. The method was successfully applied for the determination of the three drugs in their co-formulated tablets. The results were compared statistically with reference methods and no significant difference was found. The developed method is specific and accurate for the quality control and routine analysis of the cited drugs in pharmaceutical preparations.     

Determination of Nateglinide in Human Plasma by LC-ESI-MS and Its Application to Bioequivalence Study

To evaluate the bioequivalence of nateglinide, a rapid and specific liquid chromatographic-electrospray ionization mass spectrometric method was developed and validated to determine nateglinide for human plasma samples. The analyte was detected using electrospray positive ionization mass spectrometry in the selected ion monitoring mode. Tinidazole was used as the internal standard. A good linear relationship obtained in the concentration ranged from 0.05 to 16 μg mL^?1 (r ² = 0.9993). Lower limit of quantification was 0.05 μg mL^?1 using 100 μL of plasma sample. Intra- and inter-day relative standard deviations were 2.1–7.5 and 4.7–8.9%, respectively. Among the pharmacokinetic data obtained, T _max was 2.09 ± 1.06 h for reference formulation and 2.40 ± 0.97 h for test formulation. C _max was 4.17 ± 1.31 μg mL^?1 for reference formulation and 4.37 ± 1.53 μg mL^?1 for test formulation. The half-life (t _½) was 1.93 ± 0.44 h for reference formulation and 1.92 ± 0.29 h for test formulation. AUC_0–10h was 13.67 ± 4.36 μg h mL^?1 for reference formulation and 13.21 ± 4.09 μg h mL^?1 for test formulation. This method was successfully applied to the pharmacokinetic study in human plasma samples.     

N-(1-Naphthyl)ethylenediamine, a New UV Labeling Reagent Used for LC Determination of Valproic Acid in Human Plasma

A high performance liquid chromatography method is presented for the determination of valproic acid levels in human plasma. The method was based on pre-column derivatization using N-(1-naphthyl)ethylenediamine as a new labeling agent. The calibration curve was linear in the investigated concentration range between 0.1 and 100 μg mL^?1 and showed good accuracy and reproducibility. The assay provided a limit of quantification of 0.1 μg mL^?1 for valproic acid and a limit of detection of 10 ng mL^?1, respectively. The presented method was successfully applied to the determination of valproic acid levels in plasma after oral administration of 600 or 800 mg of sodium valproate.     

Development and Validation of a Stability-Indicating LC Method for Simultaneous Analysis of Aceclofenac and Paracetamol in Conventional Tablets and in Microsphere Formulations

A stability-indicating reversed-phase LC method for analysis of aceclofenac and paracetamol in tablets and in microsphere formulations has been developed and validated. The mobile phase was 80:20 (v/v) methanol–phosphate buffer (10 mM at pH 2.5 ± 0.02). UV detection was at 276 nm. The method was linear over the concentration ranges 16–24 and 80–120 μg mL^?1 for aceclofenac and paracetamol, respectively, with recovery in the range 100.9–102.22%. The limits of detection and quantitation for ACF were 0.0369 and 0.1120 μg mL^?1, respectively; those for PCM were 0.0631 and 0.1911 μg mL^?1, respectively.