Sodium Octanesulfonate Research Articles

Automated analysis of fluvoxamine in rat plasma using a column‐switching system and ion‐pair high‐performance liquid chromatography

We have established a robust, fully automated analytical method for the analysis of fluvoxamine in rat plasma using a column-switching ion-pair high-performance chromatography system. The plasma sample was injected onto a precolumn packed with Shim-pack MAYI-ODS (50 microm), where the drug was automatically purified and enriched by on-line solid-phase extraction. After elution of the plasma proteins, the analyte was back-flushed from the precolumn and then separated isocratically on a reversed-phase C18 column (L-column ODS) with a mobile phase (acetonitrile-0.1% phosphoric acid, 36:64, v/v) containing 2 mM sodium 1-octanesulfonate. The analyte was monitored by a UV detector at a wavelength of 254 nm. The calibration line for fluvoxamine showed good linearity in the range of 5-5000 ng/mL (r > 0.999) with the limit of quantification of 5 ng/mL (RSD = 6.51%). Accuracy ranged from -2.94 to 4.82%, and the within- and between-day precision of the assay was better than 8% across the calibration range. The analytical sensitivity and accuracy of this assay is suitable for characterization of the pharmacokinetics of orally-administered fluvoxamine in rats.

Monitoring of N-nitrosodiethanolamine in cosmetic products by ion-pair complex liquid chromatography and identification with negative ion electrospray ionization mass spectrometry

A high-performance liquid chromatographic (HPLC) method was developed for the determination of N-nitrosodiethanolamine (NDELA), which is a non-volatile N-nitrosoamine. In this method, sodium 1-octanesulfonate has been used as an ion complexation agent for NDELA. The resulting complex was analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC) using a Eurospher-100 C18 column (250 × 4.6 mm, 5 μm), water/acetonitrile (95/5, v/v) and UV detection at 234 nm. The detector response was linear in the range 0.03–10.00 μg mL −1 and the limit of detection was 0.01 μg mL −1. The complexation of the NDELA and sodium 1-octanesulfonate was confirmed by negative ion electrospray ionization mass spectrometry at m/ z 327 [M–Na] − and also MS/MS measurements of the resulting fragments. For real sample analyses, NDELA was measured in cosmetic products after clean up by solid-phase extraction (SPE) with C 18 cartridge for water-soluble samples and liquid–liquid extraction (LLE) by methylene chloride for less water-soluble samples. The average values for NDELA recovery by SPE and LLE were 86.9 and 51.8% and relative standard deviations (RSDs%) were 0.9 and 5.6%, respectively. The presented method is easy to use, robust and can be implemented on any reversed-phase HPLC system with UV detection.

Simultaneous Determination of Angiotensin I-Converting Enzyme Inhibitory Peptides in Tryptic Casein Hydrolysate by High-Performance Liquid Chromatography Combined with a Replicate Heart-Cut Column-Switching Technique

A replicate heart-cut column-switching HPLC method combined with two switching valves was newly developed for the simultaneous determination of three antihypertensive peptides (Ala-Phe, Tyr-Pro, and Trp-Tyr) in tryptic casein hydrolysate in one run-in assay. After a first separation on an octadecyl silane (ODS) column, heart-cuts of each peptide were individually separated on a subsequent analytical ODS column: 26% acetonitrile for Ala-Phe and Tyr-Pro (32% for Trp-Tyr) in 0.1% trifluoroacetic acid containing 10 mM sodium 1-octanesulfonate at 0.8 mL/min. Ala-Phe, Tyr-Pro, and Trp-Tyr in casein hydrolysate were determined within 70 min to be 0.377 +/- 0.037 mg/g, 2.50 +/- 0.26 mg/g, and 0.096 +/- 0.008 mg/g, respectively.

Simple and Rapid Liquid Chromatographic Method for Determination of Histidine HCl in Pharmaceutical Preparations

Histidine (HID) is frequently compounded in pharmaceutical preparations for the treatment of gastrointestinal diseases. A simple and rapid liquid chromatographic method was developed and validated for the routine determination of HID in pharmaceutical preparations. The high-performance liquid chromatographic (HPLC) system consisted of an Purospher STAR RP18 endcapped column (4.6×250 mmi. d.) using amobile phase of 50 mMphosphate buffer with 3 mM sodium octanesulfonate: acetonitrile (95:5, v/v) with an ultraviolet/visible (UV/VIS) detector at 210 nm. The developed method satisfies the system suitability criteria and peak integrity for HID. The square of the correlation coefficient of the linear regression analysis was 0.9995. The relative standard deviations (RSDs) for intra- and inter-day tests were less than 2%. The recovery for 5 concentrations expressed as the closeness of the observed mean to the spiked concentration was 98.20%~101.02%. The limits of detection (LOD) and quantitation (LOQ) for HID were 2.2 and 7.3 μg/mL, respectively. The method was applied to quantitatively determine HID in 8 brands of HID-containing tablets on the Taiwanese market, and these were found to contain 100.59%±1.01% of the percentage claimed on the label. The results indicate that the established assay method is suitable for measuring HID in pharmaceutical preparations.

Determination of Four Aminoglycoside Antibiotics by Liquid Chromatography with Pulsed Electrochemical Detection

A new and simple liquid chromatographic method using a column packed with poly(styrene‐divinylbenzene) and pulsed electrochemical detection on a gold electrode for the determination of vertilmicin sulfate (new drug), micronomycin sulfate, etimicin sulfate, and sisomicin sulfate and their related substances was developed. The mobile phase consisted of an aqueous solution of 38 g L−1 sodium sulfate, 0.4 g L−1 sodium octanesulfonate, 13 mL L−1 (10 mL L−1 for micronomycin) tetrahydrofuran, and 50 mL L−1 0.2 M phosphate buffer (pH=3). The effects of the different chromatographic parameters on the separation were investigated. The specificity, assay linearity, low level assay linearity, and precision of assay were also investigated.

The solubility of ethane in aqueous solutions of sodium 1-pentanesulfonate, sodium 1-hexanesulfonate, sodium 1-heptanesulfonate, and sodium 1-octanesulfonate at 25 °C

Measurements have been made to determine the solubility of ethane, C 2H 6, in aqueous solutions of four different surfactants of the linear alkanesulfonate class at 25 °C. The surfactants, sodium 1-pentanesulfonate, sodium 1-hexanesulfonate, sodium 1-heptanesulfonate, and sodium 1-octanesulfonate, all share a common head group ( SO − 3) and counter ion (Na +), and differ only in the length of the alkyl chain attached to the head group. The solubility of ethane has been determined as a function of surfactant concentration for each surfactant. At surfactant concentrations below the critical micelle concentration (CMC), the solubility of ethane is quite low and differs only slightly from the solubility of ethane in pure water. At concentrations greater than the CMC, the solubility of ethane exhibits a gradual increase with surfactant concentration. At high surfactant concentrations, well in excess of the CMC, the solubility of ethane is found to increase as a linear function of surfactant concentration. From this data it becomes possible to determine the fractional population of the surfactant in the free and micellized states. The solubility data measured for ethane is interpreted in terms of the mass-action model for micelle formation.

Two-Liquid Flotation: Heterocoagulation of Fine Particles in Polar Organic Solvent

The paper explains the heterocoagulation of micro-size particles and non-polar oil droplet in polar organic solvent in order to verify the mechanism of two-liquid flotation when separating fine powders. In other words, the zeta potential and the size of aggregated particles were measured, and then the total potential energy was calculated according to the DLVO theory. The results indicated that the heterocoagulation of one of fluorescent powders and n-heptane droplet in DMF solvent is feasible in the presence of surfactant ((1) in the presence of 2 � 10 � 4 mol L � 1 of DAA, heterocoagulation of green particle–n-heptane droplet, (2) in the presence of sodium 1-octanesulfonate 20 � 10 � 4 mol L � 1 , heterocoagulation of blue particle–n-heptane droplet). Based on these results, the heterocoagulation mechanism of fine particles and non-polar oil in polar organic solvent was evaluated and thus the mechanism of two-liquid flotation of fine particles was elucidated. These findings are also verified by presenting a set of experimental results regarding the separation of a mixture of fluorescent powders.

HPLC Method for Determination of 3,4-Diaminopyridine in the Presence of Related Substances and Degradation Products Formed Under Stress Conditions

3,4-Diaminopyridine is used to treat some symptoms met in Lambert Eaton myasthenia syndrome. It was shown efficient to reduce a form of variable muscle weakness and fatigability typical of the disease and correlated to a block of acetylcholine release. A high performance liquid chromatographic method for the determination of 3,4-diaminopyridine in the presence of related substances and its degradation products is described. The method is based on the use of a C18 bonded phase column and a mobile phase composed of 10 volumes of acetonitrile and 90 volumes of an aqueous solution containing 1 g L−1 sodium octanesulfonate and 0.77 g L−1 ammonium acetate. The pH of the aqueous solution was adjusted to 1.9 with trifluoracetic acid. All peaks are eluted in <40 min. The method was demonstrated to be precise, accurate and specific even though a major part of the drug is decomposed. The results indicate that the proposed method could be used in stability assays.

Simultaneous determination of celecoxib, meloxicam, and rofecoxib using capillary electrophoresis with surfactant and application in drug formulations

A simple and selective CE using surfactant with UV detection is described for the simultaneous determination of selective cyclooxygenase-2 inhibitors, celecoxib, meloxicam, and rofecoxib. The simultaneous analysis of celecoxib, meloxicam, and rofecoxib was performed in Tris buffer (10 mM; pH 11) with 60 mM sodium octane-sulfonate and 20% ACN as an anionic surfactant and organic modifier, respectively. Under this condition, good separation with high efficiency and the required short analysis time is achieved. The linear ranges of the method for the determination of celecoxib, meloxicam, and rofecoxib were over 5-100 microg/mL; the detection limits at 200 nm (S/N = 3; injection 3.45 kPa, 5 s) were 2, 1, and 1 microg/mL, respectively. The small amount of sample required and the expeditiousness of the procedure allow content uniformity to be determined in individual pharmaceutical products.

Chiral Ligand-Exchange Chromatography for Separation of Three Stereoisomers of Octahydroindole-2-carboxylic Acid

A novel HPLC method is described for separation of the three stereoisomers of octahydroindole-2-carboxylic acid (Oic), an intermediate in the synthesis of perindopril. The chiral mobile phase contained the complex of Cu(II) with the optically active selector L-phenylalaninamide (L-PheA), and an ion-pair reagent, sodium 1-octanesulfonate. The effects of the concentrations of the Cu(II)–L-PheA complex and the ion-pair reagent, mobile phase pH, ionic strength, acetonitrile content, and column temperature were studied. Satisfactory resolution was achieved for three stereoisomers, RRR-, SSS-, and SRR-Oic.

Analysis of neomycin using an improved liquid chromatographic method combined with pulsed electrochemical detection

An isocratic liquid chromatographic method with pulsed electrochemical detection is described for the determination of neomycin in the presence of its impurities. The mobile phase is composed of an aqueous solution containing 35 g/l of sodium sulphate, 1 g/l of sodium 1-octanesulfonate, 14 ml/l of tetrahydrofuran (THF) and 50 ml/l of 0.2 M phosphate buffer pH 3.0. Sodium hydroxide was added post column to enhance the detection. An investigation of different reversed-phase columns indicated that the Discovery (C18 5 microm, 250 mm x 4.6 mm I.D.) column was the most suitable. The proposed method shows high efficiency, allowing the separation of the main component neomycin B from neomycin C and 15 other impurities. A central composite design was used to assess the robustness of the method. The method showed good selectivity, repeatability, linearity and sensitivity. This method was applied to analyse commercial samples.

Determination of indomethacin in plasma by micellar electrokinetic chromatography with UV detection for premature infants with patent ducts arteriosus

A simple and selective micellar electrokinetic chromatography (MEKC) is described for determination of indomethacin in plasma. Plasma proteins are precipitated by acetonitrile. An aliquot of supernatant was evaporated and reconstituted with Tris buffer for MEKC analysis. The separation of indomethacin was performed at 25 degrees C using a background electrolyte consisting of Tris buffer (30 mM; pH 8.0) with 100 mM sodium octanesulfonate (SOS) as an anionic surfactant. Under this condition, a good separation with high efficiency and short analysis time is achieved. Several parameters affecting the separation of indomethacin were studied, including pH and concentrations of the Tris buffer and SOS. The linear range of the method for the determination of indomethacin was over 0.3-10.0 microg/mL; the detection limit (signal-to-noise ratio=3; injection 0.5 psi 5s) was 0.1 microg/mL. The proposed method for determination of indomethacin in premature infants with patent ducts arteriosus has been demonstrated.

Determination of donepezil hydrochloride in human and rat plasma, blood and brain microdialysates by HPLC with a short C 30 column

A simple and sensitive HPLC method with fluorescence (FL) detection for determination of donepezil (DP) in plasma and microdialysate samples was developed. A rapid isocratic separation of DP could be achieved by a short C 30 column using mobile phases of 25 mM citric acid/50 mM Na 2HPO 4 (pH 6.0)–CH 3CN (73:27%, v/v) containing 3.5 mM sodium 1-octanesulfonate for plasma and H 2O–CH 3CN–CH 3OH (80:17:3%, v/v/v) containing 0.01% acetic acid for microdialysate. The eluate was monitored at 390 nm with an excitation at 325 nm. The detection limits (S/N = 3) of DP for human plasma, rat plasma and rat brain or blood microdialysates were 0.2, 1.0 and 2.1 ng/ml, respectively. Reproducible results could be obtained by using (±)-2-[(1-benzyl-piperidine-4-yl)ethyl]-5,6-dimethoxyindan-1-one hydrochloride as an internal standard (IS). The method was successfully applied for monitoring of DP levels in rat plasma, blood and brain microdialysates and patient plasma.

Online photocatalytic device for highly selective pre-column fluorescence derivatization of 5-hydroxyindoles with benzylamine

A fluorimetric liquid chromatographic method for the determination of 5-hydroxyindoles based on the benzylamine derivatization process mediated through an online photocatalytic oxidation has been developed. In this study, we used a photocatalytic column comprising tefzel tubing packed with TiO 2-coated glass beads, as a pre-column derivatization reactor. The fluorescence derivatization of 5-hydroxyindoles using benzylamine proceeded during their passage through the reaction column under near-UV irradiation. The 5-hydroxyindole derivatives were separated continuously on a reversed-phase liquid chromatography within 50 min, using 100 mM acetate buffer (pH 4.6)–acetonitrile (72:28, v/v; isocratic elution) containing 3 mM sodium octanesulfonate; the samples were detected fluorimetrically at 465 nm upon excitation at 350 nm. The detection limits (signal-to-noise ratio = 3) of the 5-hydroxyindoles were in the range from 160 to 360 fmol per 5 μL injection. We have applied this method, which requires minimal sample pre-treatment, to the determination of 5-hydroxyindole-3-acetic acid in human urine.

Development and validation of a new reversed-phase ion pairing liquid chromatographic method with fluorescence detection for penciclovir analysis in plasma and aqueous humor

A simple, sensitive and reliable HPLC ion-pairing method with fluorescence detection, was developed for penciclovir determination in plasma and aqueous humor, with a Zorbax SB-aq C18 (100 mmx2.1 mm) column. Plasma samples were treated by solid-phase extraction with Oasis MCX (30 mg) cartridges. Ganciclovir, an antiviral drug structurally related to penciclovir, was used as internal standard (I.S.). Aqueous humor samples were directly injected into the chromatographic system. Separation was performed by a gradient elution with a mobile phase consisting of a mixture of acetonitrile and phosphate buffer 50mM containing 5mM of sodium octanesulfonate, pH 2.0, at a flow rate of 0.3 ml/min. The method was validated and showed good performances in terms of linearity, sensitivity, precision and trueness. Quantification limit was obtained at 0.05 microg/ml for aqueous humor and at 0.1 microg/ml for plasma. Finally, the proposed analytical method was used to measure penciclovir in clinical samples for a pharmacokinetic study, after oral administration of famciclovir.

Determination of Antihypertensive Small Peptides, Val-Tyr and Ile-Val-Tyr, by Fluorometric High-Performance Liquid Chromatography Combined with a Double Heart-Cut Column-Switching Technique

A double column-switching HPLC method with naphthalene-2,3-dialdehyde (NDA) was applied for determination of two plasma antihypertensive peptides, Val-Tyr (VY) and Ile-Val-Tyr (IVY). After a first separation on a Phe-ODS column, double heart-cuts of the retention time corresponding to NDA-VY and NDA-IVY elutions were successfully separated on an analytical ODS column: 60% acetonitrile in 0.1% trifluoroacetic acid containing 5 mM sodium 1-octanesulfonate at 1.0 mL/min. Within-run coefficients of variation were 1.73% and 4.73% for VY and IVY, respectively.

Effect of lipophilic counter-ions on membrane diffusion of benzydamine

Many topically applied drugs are ionized molecules that exhibit poor penetration across the lipid domains of the stratum corneum. Reduction of the charge on the molecule would be expected to enhance skin penetration. The objective of this study was to investigate the interaction of the non-steroidal anti-inflammatory drug benzydamine hydrochloride with suitable counter-ions including ibuprofen sodium. The influence of pH of the donor solution and hence degree of ionization on partitioning between n-octanol:buffer and the flux of benzydamine hydrochloride across polydimethyl siloxane (PDMS) membrane and human epidermis was determined. The maximum flux was determined at pH 7.6 when the fraction unionized was 2.51%, rather than at pH 9 when the fraction unionized was 38.7%. This suggests that at higher pH, although the permeability coefficient is increased, the decrease in solubility and therefore concentration of dissolved benzydamine in the medium results in a decrease in flux across the PDMS membrane. Ion-pair formation or interaction with each of the counter-ions was confirmed by NMR spectroscopy. Significant increases in log P and flux across PDMS membrane were determined for the ion-pairs (0.087, 12.54, 11.31, 0.121 μg cm −2 h −1 for benzydamine hydrochloride and ion-pairs with ibuprofen sodium, sodium benzoate and sodium octane sulfonate respectively). This study shows that it is possible to significantly enhance the flux of salts across a lipophilic membrane in the presence of counter-ions, resulting from intermolecular interaction and/or ion-pair formation.

HPLC를 이용한 시판 아테놀롤 원료 및 제품 중 유연물질의 분석

Atenolol and related compounds found in raw materials and commercial products were analyzed by reversed-phase high-performance liquid chromatography. A mixed solution of phosphate buffer (3.4 g/l, pH 3.0), tetrahydrofurane and methanol (800:20:180, v/v/v) including sodium octanesulfonate (1 g/l) and tetrabutylammonium-hydrogensulfate (0.4 g/l) was used as mobile phase at the flow rate of 0.25 ml/min. Detection was carried out at UV 226 nm. Atenolol related compounds, such as bis ether, tertiary amine and blocker acid were identified by comparing the retention time of the standard. The within-day and between-day precisions of the separated compounds were less than 1.2% and 3.4%, respectively. The contents of related compounds of the tested samples were under the limit prescribed in the European Pharmacopoeia. The pattern of the related compounds showed that atenolol raw materials and products could be classified in three different groups, indicating that the materials originated from different source or treated in different way.

HPLC analysis of pheomelanin degradation products in human urine.

A sensitive and specific high performance liquid chromatography (HPLC) method was developed to quantify 4-amino-3-hydroxyphenylalanine (4-AHP) and 3-amino-4-hydroxyphenylalanine (3-AHP) in urine. In degradation studies of melanin pigment, 4-AHP and 3-AHP are derived from benzothiazine units of pheomelanin and pheomelanin-related metabolites such as trichochromes. 5-S-Cysteinyldopa-derived benzothiazine products give 4-AHP while 2-S-cysteinyldopa-derived benzothiazine products give 3-AHP. 3-AHP is also derived from nitrotyrosine formed by nitration of tyrosine with reactive nitrogen species. For this reason, the influence of this biological process on the amount of 3-AHP found in biological material have been investigated. The method is based on hydriodic acid hydrolysis of the melanin polymer and reversed-phase HPLC with electrochemical detection of the degradation products 4-AHP and 3-AHP. The mobile phase consists of 25 mM ammonium acetate and sodium octanesulfonate as an ion-pairing reagent. The 4-AHP and 3-AHP peaks were well separated and the detector response was linear within the range 0-2 ng injected for both compounds. With the developed chromatographic system, 4-AHP and 3-AHP showed good separation in the biological samples. There was a strong correlation between 4-AHP and 3-AHP in the urine of 50 malignant melanoma patients and two healthy subjects (R0.977). The two compounds were also strongly correlated with 5-S-cysteinyldopa in urine, the correlation coefficients being 0.862 and 0.907, respectively. The method described is sensitive enough for analysis of pheomelanin in urine and in several other biological samples. The results indicate that 3-AHP in urine is not influenced by excreted 3-nitrotyrosine and the data indicate that pheomelanins are excreted in the urine of melanoma patients.

Sorption/diffusion behaviour of anionic surfactants in polyacrylamide hydrogels: from experiment to modelling

The sorption and diffusion processes of anionic surfactants with different chain length through polyacrylamide hydrogels with low swelling degree have been studied by electrical conductivity measurements. The multicomponent equilibrium equation has been used to model the sorption isotherms of different anionic surfactant in the hydrogels. Such isotherms show that initial rapid sorption of unimer surfactant into the membranes occurs, suggesting that non-freezing water can be involved in these interactions. In aqueous solution, at concentrations near and above the critical micelle concentration an anti-co-operative region is found. The diffusion coefficients of the anionic surfactants inside the hydrogel matrix show that the mobility of diffusing surfactant entities is dependent on cross-linker concentration and chain length. The Cukier hydrodynamic model and the free volume theory as modified by Peppas and Reinhart were applied to explain the dependence of the diffusion coefficients of surfactant on surfactant concentration inside the hydrogel. The hydrodynamic model was applied with success to the more hydrophilic surfactant, sodium 1-octanesulfonate, showing that the diffusion coefficients, D, increase when the resistance to hydrodynamic medium decreases; when the surfactant chain length increases (sodium dodecyl sulfate and sodium 1-hexadecane sulphonate) the variation of D with the free volume can only be understood considering the sieving effect produced by the surfactant inside gel.