Use of Capillary Gas Chromatography for Determining Hydrocarbons in High-Purity Silane

A procedure was proposed for the 2D gas-chromatographic determination of C₁-C₄ hydrocarbons in high-purity silane. The impurities were separated in a capillary column with a newly proposed adsorbent, poly(trimethylsilylpropyne). The detection limits for the impurities are (2?6) × 10^?7 vol %, which is 2.5–15 times lower than those found in the literature.     

The analysis of major impurities of lipophilic-conjugated phosphorothioate oligonucleotides by ion-pair reversed-phase HPLC combined with MALDI-TOF-MS

A simple and rapid ion-pair reversed phase high-performance liquid chromatography (IP-RP-HPLC) method was developed to analyse the major impurities of lipophilic-conjugated phosphorothioate oligonucleotides (ODNs), which provided better separation performance than capillary gel electrophoresis and ion exchange chromatograph methods. The study showed that covalent conjugations of lipophilic group (docosanyl, C₂₂) to ODN at 5′-termini (denoted as 5′C₂₂-Flu) or 3′-termini (denoted as 3′C₂₂-Flu) exhibited similar chromatographic retention behavior. Some important analytical conditions of IP-RP-HPLC, including column type, ion-pairing buffer composition, and separation temperature, were investigated for the effects on the separation of crude 5′C₂₂-Flu. As expected, the method developed was successfully applied to the analysis of crude 3′C₂₂-Flu and both purified products. Furthermore, the related impurities derived from the synthetic process were identified by matrix-assisted laser desorption-ionization time-of-flight mass spectrum. These MS results are of benefit to understanding the major process-related impurities in lipophilic-ODN conjugates synthesis, thereby elevating the quality of target products.     

The investigation and application of the packed glass capillary column with a core

A new type of packed glass capillary column (PGCC) with a core, and its potential usage in practice are described. The permeability of the column is considerably greater than that of conventional PGCC and its N/(P_i-P_o) value is also higher. This novel PGCC column has been successfully applied to the analysis of trace levels of ethyne, cyclopropane, propadiene, propyne, and other C₁? C₄ impurities in pure ethene, propene, 1,3-butadiene, and catalytic cracking gas samples as well as other petrochemical gases such as liquified petroleum gas.     

Detailed hydrocarbon analysis of gasoline by GC-MS (SI-PIONA)

A gas chromatographic – mass spectrometric (GC-MS) method has been developed for detailed analysis of the hydrocarbon content of gasoline. The method is equipped with special software and includes the analysis of oxygenated compounds in a single run. The technique utilizes three basic components: the separating power of high resolution capillary gas chromatography, a mass spectrometer with a controllable ion source and ion fragmentation ratios, and unique software for data handling and preparation of reports. The C₄ to C₁₂ range of hydrocarbons in gasoline is covered by the method. A sample of unleaded gasoline from a gas station was analyzed without sample preparation. The results are discussed.     

Determination of trace volatile fatty acids in ambient air by capillary gas chromatography–mass spectrometry in SIM mode

A simple, rapid and sensitive method was developed and validated for the analysis of C₂–C₅ volatile fatty acids (VFAs) in ambient air. This method involves preconcentration of VFAs with a sodium carbonate-impregnated silica gel tube, ultrasonic extraction with pure water, partition of VFAs to diethyl ether and determination using gas chromatography with a mass selective detector in the selected ion monitoring mode. A water-resistant free fatty acid phase capillary column was used to directly separate C₂–C₅ VFAs without the time-consuming derivatisation process. The limits of detection ranged from 0.001 to 0.003 µg m^?3 and the limits of quantification ranged from 0.003 to 0.010 µg m^?3. The validated method was successfully applied to the analysis trace-level VFAs in ambient air and in air samples from a landfill with perceived odour pollution.     

Development and Validation of a New LC Method for Analysis of Brimonidine Tartrate and Related Compounds

A novel liquid chromatographic method for analysis three potential impurities in brimonidine tartrate drug substance has been developed and validated. Efficient chromatographic separation was achieved on a C₈ column (250 mm × 4.6 mm, 5-μm particles) with a simple mobile-phase gradient at a flow rate of 1.0 mL min⁻¹. Quantification was achieved by use of ultraviolet detection at 248 nm. Resolution between brimonidine tartrate and its three potential impurities was greater than 3.0. Regression analysis showed the r value (correlation coefficient) was >0.999 for brimonidine and its three impurities. The method was capable of detecting all three impurities of brimonidine tartrate at levels below 0.07 μg in a test concentration of brimonidine tartrate of 1.0 mg mL⁻¹ and for an injection volume of 10 μL. A solution of brimonidine tartrate in acetonitrile–water 2:8 (v/v) was stable for 48 h. The drug was subjected to stress conditions as prescribed by the ICH. Degradation was found to occur slightly under oxidative stress conditions but the drug was stable to aqueous, acidic, and basic hydrolysis, and photolytic and thermal stress. The assay of the stressed samples was calculated relative to a qualified reference standard and the mass balance was found close to 99.8%. The method was validated for linearity, accuracy, precision, and robustness.

     

Analysis of light hydrocarbons C1–C5 with Porous Layer Open Tubular fused silica columns of aluminum oxide. Part 1: The column

A method is described for the preparation of a Porous Layer Open Tubular (PLOT) fused silica column coated with submicron particles of aluminum oxide for the analysis of light hydrocarbons. The column is thermally stable and provides reproducible analytical data over a long period of time. The column can be operated at temperatures easily controlled by commercially available gas chromatographic apparatus. 1,3-Butadiene is retarded much more than its principal impurities: thus the polarity of aluminum oxide is extremely useful for butadiene analysis because none of the contaminants is obscured by the butadiene peak. The analysis of the 16 most common C₁–C₄ hydrocarbons is achieved within 5 min at 60°C with helium as the carrier gas. Conditioning of the carrier gas with water vapor from CuSO₄.5H₂O to decrease the activity of the aluminum oxide is described. Some applications of a 30 m × 0.32 mm aluminum oxide PLOT column are given.     

Analysis of Spectinomycin by HPLC with Evaporative Light-Scattering Detection

A high-performance liquid chromatographic method with evaporative light-scattering detection (ELSD) has been developed for analysis of spectinomycin and related impurities. Separation of spectinomycin from structurally related impurities was achieved on a C₁₈ column. The optimized mobile phase was 25 mmol L⁻¹ ammonium acetate (pH 7.5)-methanol, 90:10 (v/v), at a flow rate of 0.6 mL min⁻¹. The temperature of the drift tube of the ELSD was 95°C and the flow rate of carrier gas was 2.2 L min⁻¹. The accuracy, specificity, precision, linearity, sensitivity, and robustness of the method were validated in accordance with ICH guidelines. In addition to determination of spectinomycin and related impurities, the method is also ideal for determination of the salts spectinomycin hydrochloride and spectinomycin sulfate.     

CZE Determination of Mismatched Double-Stranded Oligonucleotides (poly I:poly C12U) in Beagle Serum

A capillary zone electrophoretic (CZE) method with diode-array detection has been established for analysis of mismatched double-stranded oligonucleotides, poly I:poly C₁₂U, in beagle serum. The effects of sample pretreatment, buffer pH, buffer concentration, and applied voltage on the separation of inosine were optimized. Baseline separation was obtained for inosine within 11 min by use of 0.05 mol L^?1 borate running buffer, pH 9.60, and an applied voltage of 25 kV at 25 °C; the detection wavelength was 254 nm. To evaluate the performance of the method and demonstrate the utility of the approach, an experiment was designed in which poly I:poly C₁₂U were added to serum at different concentrations, artificially creating groups of samples. The proposed CZE method seemed a powerful technique for kinetic study of poly I:poly C₁₂U in serum.     

Development and Validation of a New LC Method for Analysis of Brimonidine Tartrate and Related Compounds

A novel liquid chromatographic method for analysis three potential impurities in brimonidine tartrate drug substance has been developed and validated. Efficient chromatographic separation was achieved on a C₈ column (250 mm × 4.6 mm, 5-μm particles) with a simple mobile-phase gradient at a flow rate of 1.0 mL min^?1. Quantification was achieved by use of ultraviolet detection at 248 nm. Resolution between brimonidine tartrate and its three potential impurities was greater than 3.0. Regression analysis showed the r value (correlation coefficient) was >0.999 for brimonidine and its three impurities. The method was capable of detecting all three impurities of brimonidine tartrate at levels below 0.07 μg in a test concentration of brimonidine tartrate of 1.0 mg mL^?1 and for an injection volume of 10 μL. A solution of brimonidine tartrate in acetonitrile–water 2:8 (v/v) was stable for 48 h. The drug was subjected to stress conditions as prescribed by the ICH. Degradation was found to occur slightly under oxidative stress conditions but the drug was stable to aqueous, acidic, and basic hydrolysis, and photolytic and thermal stress. The assay of the stressed samples was calculated relative to a qualified reference standard and the mass balance was found close to 99.8%. The method was validated for linearity, accuracy, precision, and robustness.     

The Analysis of volatile compounds by purge and trap with whole column cryotrapping (WCC) on a fused silica capillary column

The purge and trap (P&T) method of analysis has been interfaced with fused silica capillary column gas chromatography. This interfacing has been accomplished without splitting the P&T trap desorption carrier gas. Thus, 100% of the purged compounds are transferred to the column. The analytes are cryofocussed on the column using whole column cryotrapping (WCC) at ?80°C. The resulting P&T/WCC procedure is extremely well-suited to the analysis of trace purgeable aqueous organic compounds. Samples and standards containing a variety of aromatic standard compounds were analyzed. The standards included benzene, toluene, ethylbenzene, xylenes, C₃-C₄-benzenes, and naphthalene, as well as three P&T internal standard compounds. Chromatographic peak widths were uniformly less than 6 s at the base and excellent precision was obtained in the relative retention time data for all compounds. The chromatogram of a groundwater sample contaminated with aromatic gasoline compounds is also presented. Since P&T/WCC works well with fused silica capillary columns, the full sensitivity and chromatographic efficiency of capillary gas chromatography is made available to P&T analyses.     

CZE Determination of Mismatched Double-Stranded Oligonucleotides (poly I:poly C12U) in Beagle Serum

A capillary zone electrophoretic (CZE) method with diode-array detection has been established for analysis of mismatched double-stranded oligonucleotides, poly I:poly C₁₂U, in beagle serum. The effects of sample pretreatment, buffer pH, buffer concentration, and applied voltage on the separation of inosine were optimized. Baseline separation was obtained for inosine within 11 min by use of 0.05 mol L⁻¹ borate running buffer, pH 9.60, and an applied voltage of 25 kV at 25 °C; the detection wavelength was 254 nm. To evaluate the performance of the method and demonstrate the utility of the approach, an experiment was designed in which poly I:poly C₁₂U were added to serum at different concentrations, artificially creating groups of samples. The proposed CZE method seemed a powerful technique for kinetic study of poly I:poly C₁₂U in serum.

     

Improving the Detectability of Sequential Injection Chromatography (SIC): Determination of Triazines by Exploiting Liquid Core Waveguide (LCW) Detection

Coupling a liquid core waveguide cell to a sequential injection chromatograph improved the detection limits for determination of triazine herbicides without compromising peak resolution. Separation of simazine, atrazine, and propazine was achieved in water samples by a 25 mm long C₁₈ monolithic column. Detection was made at 238 nm using a type II LCW (silica capillary coated with Teflon® AF2400) cell with 100 cm of optical path length. Detection limits for simazine, atrazine, and propazine were 2.3, 1.9, and 4.5 µg L^?1, respectively. Reduced analysis time and low solvent consumption are other remarkable features of the proposed method.     

A Chemometrical Approach to Optimization and Validation of an HPLC Assay for Rizatriptan and its Impurities in Tablets

Abstract

An isocratic reversed‐phase high‐performance liquid chromatographic method was developed and validated for the analysis of a novel antimigraine drug, rizatriptan benzoate, in a dosage form along with its two impurities, L‐749.019 and L‐783.540. The method used a C₁₈ XTerra? (150×3.9 mm), 5 µm column. The mobile phase consisted of a mixture of methanol, TEA (1%) and 10 mM KH₂PO₄ (5:9.5:85.5 v/v) at a flow rate of 1.2 ml min^?1 (pH of the water phase was adjusted to 5.5 with 85% orthophosphoric acid). Column temperature was 20°C and the detection was performed at 225 nm. The central composite design technique and the response surface method were used in the robustness test considerations. The method was applied satisfactorily to the analysis of commercial rizatriptan formulation.     

Theoretical analysis on yellow emission of gallium nitride with vacancy defects or impurities

The absorption and the emission spectra of wurtzite GaN with some vacancy defects or impurities (V_Ga, V_Ga–O_N, V_Ga–H, V_N, V_N–H, C_Ga, C_N, C_i, Si_Ga, O_N) were calculated by using TDDFT method with cluster models. Ga₂₆N₂₆H₅₀ cluster is chosen as a basic cluster according to the predicted energy gap. The TD-B3LYP calculation results show that yellow emission of about 2.2 eV of GaN material attributes to the presence of V_Ga–O_N complex. The other vacancy defects or impurities bring out emission of about 2.0–2.1 eV or have no effect on yellow emission of GaN.     

Eine neue Methode zur stereochemischen Analyse offenkettiger terpenoider Carbonyl-Verbindungen,

A New Method for the Stereochemical Analysis of Acyclic Terpenoid Carbonyl Compounds A new method for the determination of the enantiomeric and diastereoisomeric composition of terpenoid carbonyl compounds is presented. Separation of the diastereoisomeric (+)-L -diisopropyl-tartrate acetals derived from dihydrocitronellal ( 6 ), hexahydropseudoionone ( 3 ), hexahydrofarnesal ( 7 ), and hexahydro far nesy lace tone ( 4 ), the C₁₀, C₁₃, C₁₅, and C₁₈ intermediates in various syntheses of naturally occurring tocopherols and vitamin K₁, can be achieved by capillary GC on a cyanopropylsilicon-coated glass column under standardized conditions. This technique, presenting a significant improvement over existing methodologies, is considered to be particularly useful for the analysis of highly enriched samples, typically obtained by present-day asymmetric synthesis. With reproducibilities of ± 0.3%, and, therefore, safe for routine analysis, the complete Stereochemical characterization of terpenoids with 15 and 18 C-atoms bearing two stereogenic centres is performed in a single operation for the first time.     

A Stability-Indicating LC Method for Analysis of Balsalazide Disodium in the Bulk Drug and in Pharmaceutical Dosage Forms

A novel, sensitive, stability-indicating gradient RP-LC method has been developed for quantitative analysis of balsalazide disodium and its related impurities both in the bulk drug and in pharmaceutical dosage forms. Efficient chromatographic separation was achieved on a C₁₈ stationary phase with a simple mobile-phase gradient prepared from methanol and phosphate buffer (10 mm potassium dihydrogen orthophosphate monohydrate, adjusted to pH 2.5 by addition of orthophosphoric acid). The mobile-phase flow rate was 1.0 mL min^?1. Quantification was achieved by use of ultraviolet detection at 240 nm. Under these conditions resolution of balsalazide disodium from its three potential impurities was greater than 2.0. Regression analysis resulted in a correlation coefficient greater than 0.99 for balsalazide disodium and all three impurities. This method was capable of detecting the three impurities at 0.003% of the test concentration of 0.3 mg mL^?1, using an injection volume of 10 μL. Inter-day and intra-day precision for all three impurities and for balsalazide disodium was within 2.0% RSD. Recovery of balsalazide disodium from the bulk drug (99.2–101.5%) and from pharmaceutical dosage forms (99.8–101.3%), and recovery of the three impurities (99.1–102.1%) was consistently good. The test solution was found to be stable in 70:30 (v/v) methanol–water for 48 h. When the drug was subjected to hydrolytic, oxidative, photolytic, and thermal stress, acidic and alkaline hydrolysis and oxidizing conditions led to substantial degradation. The RP-LC method was validated for linearity, accuracy, precision, and robustness.     

Ionic liquids versus ionic liquid-based surfactants in dispersive liquid–liquid microextraction for determining copper in water by flame atomic absorption spectrometry

This work compares the performance of dispersive liquid–liquid method (DLLME) as a prior step for determining copper by flame atomic absorption spectrometry (FAAS), when using the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (C₄MIm-PF₆) or the IL-based surfactant 1-hexadecyl-3-butylimidazolium bromide (C₁₆C₄Im-Br) as extractant solvents. For the water-insoluble C₄MIm-PF₆, the most conventional DLLME mode using acetonitrile as dispersive solvent was employed. For the water-soluble C₁₆C₄Im-Br, the in situ DLLME mode with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf₂) as metathesis reagent was employed. In both approaches, some effective parameters such as volumes of extractant and dispersive solvents, concentration of complexing agent, pH of sample solution, salting-out effect and final diluting solvent to ensure compatibility with FAAS, were properly optimised. The optimum conditions for the IL-DLLME method using C₄MIm-PF₆ were: 100 μL of neat C₄MIm-PF₆, 1 mL of acetonitrile, 10 mL of water, no control of pH for environmental waters, NaCl content of 23 g L^?1, diethyl dithiocarbamate (DDTC) as complexing agent at 10 mg L^?1 and final dilution of the micro-droplet with acetonitrile up to 70 µL. The optimum conditions for the in situ IL-DLLME method using C₁₆C₄Im-Br were: 0.8 mL of acetonitrile, 10 mL of water containing C₁₆C₄Im-Br at 25.2 mmol L^?1, final dilution step of the micro-droplet with 200 µL of acetonitrile and remaining conditions as those of C₄MIm-PF₆. The analytical performance of both methods was similar, being slightly better for the IL-DLLME method using C₄MIm-PF₆, with limits of detection (LOD) of 3.3 µg L^?1 (versus 5.1 µg L^?1 when using C₁₆C₄Im-Br), precision values as intraday relative standard deviation (RSD in %) lower than 8.8% (being of 10% for the C₁₆C₄Im-Br method) and an enrichment factor of 54 (being 27 when using C₁₆C₄Im-Br). The DLLME-FAAS method with C₄MIm-PF₆ was used in the analysis of environmental waters with successful performance, with relative recoveries of 110% and 105%, and interday precision with RSD values of 21% and 7.4% for spiked levels of 60 and 160 µg L^?1, respectively. The results obtained when analysing an urban wastewater sample coming from an inter-laboratory exercise was comparable to those obtained for other 93 laboratories. The method was also valid for the determination of Cu²⁺ in presence of foreign ions commonly found in natural waters.     

Development of a Simple,Rapid, and Robust Isocratic Liquid Chromatographic Method for the Determination of Pyrimethamine and its Synthetic Impurities in Bulk Drugs and Pharmaceutical Formulations

Pyrimethamine is an important antiparasitic drug in the treatment of malaria and toxoplasmosis and is often used in combination with either sulfadoxine, sulfalene, or sulfadiazine. Determining the content of pyrimethamine and investigating the related substances is currently possible applying either a compendial monograph utilizing thin layer chromatography as well as liquid chromatographic methods used by the respective manufacturers. To provide a simple method which is capable of determining the content of pyrimethamine and of resolving four of its potential synthetic impurities a very simple, cheap, precise, and accurate isocratic RP-HPLC method was developed. All analytes can be separated within a total runtime of 30 min and the method was linear within the concentration ranges of 0.12–0.740, 0.104–0.621, 0.120–0.710, 2.0–11.8, and 1.01–5.80 µg mL^?1 for pyrimethamine, impurity A, impurity B, impurity C, and impurity D, respectively. These substances were separated by employing a Eurospher-II C₁₈H column (250 × 4.6 mm, 5 µm particle size), a mobile phase being a mixture of a 0.05 M KH₂PO₄ buffer solution (pH 2.6) and methanol in the ratio 40:60 (v/v). The analysis was carried out at 30 °C, applying a flow rate of 1.2 mL min^?1, and a detection wavelength of λ = 215 nm. The coefficients of determinations (R ²) for the five analytes were greater than 0.994 for pyrimethamine and all impurities. Results of recovery studies were within the range of 89.1–105.1% for all substances. In all tested genuine batches of pyrimethamine raw material impurities within the specified limits were present which is concurrent with results obtained from using the present manufacturer’s method.     

Determination of impurities in remoxipride by capillary electrophoresis using UV-detection and LIF-detection; principles to handle sample overloading effects

Summary A capillary electrophoresis method for determination of remoxipride-related impurities was developed using a dynamically tetraalkylammonium-coated C₈ capillary. The shape of the overloaded principal peak was regulated by substituting tetraalkylammonium ions of different size for sodium ions, thereby altering the conductivity in the background electrolyte. An adequate separation of the compounds was obtained after addition of methyl-β-cyclodextrin as structural selector in combination with a reversed electroosmotic flow. The detection level for the impurities was 0.05 % (w/w) with the Beckman Pace 2100 using UV-detection. The limit of detection was substantially improved for the fluorescent compound FLA 797 using a LIF-detector equipped with a He-Cd laser as excitation source achieving detection levels below 0.0005 %. Presented at the 6th International Symposium on High Performance Capillary Electrophoresis, Jan. 31–Feb. 4 1994, San Diego, USA.