Determination of residual solvents in pharmaceuticals by thermal desorption-GC/MS.

A novel method for the determination of residual solvents in pharmaceuticals by thermal desorption (TD)-GC/MS has been established. A programmed temperature pyrolyzer (double shot pyrolyzer) is applied for the TD. This method does not require any sample pretreatment and allows very small amounts of the sample. Directly desorbed solvents from intact pharmaceuticals (ca. 1 mg) in the desorption cup (5 mm x 3.8 mm i.d.) were cryofocused at the head of a capillary column prior to a GC/MS analysis. The desorption temperature was set at a point about 20 degrees C higher than the melting point of each sample individually, and held for 3 min. The analytical results using 7 different pharmaceuticals were in agreement with those obtained by direct injection (DI) of the solution, followed by USP XXIII. This proposed TD-GC/MS method was demonstrated to be very useful for the identification and quantification of residual solvents. Furthermore, this method was simple, allowed rapid analysis and gave good repeatability.     

Determination of residual solvents in bulk pharmaceuticals by thermal desorption/gas chromatography/mass spectrometry

Thermal desorption (TD) techniques followed by capillary GC/MS were applied for the analysis of residual solvents in bulk pharmaceuticals. Solvents desorbed from samples by heating were cryofocused at the head of a capillary column prior to GC/MS analysis. This method requires a very small amount of sample and no sample pretreatment. Desorption temperature was set at the point about 20 degrees C higher than the melting point of each sample individually. The relative standard deviations of this method tested by performing six consecutive analyses of 8 different samples were 1.1 to 3.1%, and analytical results of residual solvents were in agreement with those obtained by direct injection of N,N-dimethylformamide solution of the samples into the GC. This novel TD/GC/MS method was demonstrated to be very useful for the identification and quantification of residual solvents in bulk pharmaceuticals.     

An Investigation on the Concentration Efficiencies of Some Macroreticular and Ambersorb Resins Using Radio-Labelled Organic Contaminants Commonly Encountered in Water

Abstract

The extraction efficiencies of the three commercially available Ambersorb®, carbonaceous, polymeric resins, XE-340, XE-347 and XE-348 were evaluated for their use as sorbents for environmental pollutants using four model, radio-labelled water-borne organic contaminants. Their accumulation behaviour was compared with that of the thoroughly-studied Amberlite®, macroreticular XAD-2 (hydrophobic) and XAD-7 (hydrophilic) resins. These model compounds were desorbed from the resins using known volumes of commonly-used solvents to select the solvent for a particular resin(s). In this preliminary study, at <4 μg/L concentrations of the labelled compounds in aqueous solution (pH 5.78), the order of extraction efficiency of the resins was found to be XAD-2 > XAD-7 > XE-340?-347?-348 for organics. Several inherent impurities originally present in the carbonaceous resins were desorbed by solvents during elution. These resins therefore required exhaustive soxhlet purification prior to use. Most of the impurities were identified by gas chromatography/mass spectrometry.     

Application of a monolithic silica capillary adsorbent for the preconcentration of airborne trichloroethylene and tetrachloroethylene

Monolithic silica with a bimodal pore structure was prepared in a fused silica capillary by the sol-gel process and investigated as an adsorbent for the preconcentration of airborne trichloroethylene and tetrachloroethylene. The airborne trichloroethylene and tetrachloroethylene are adsorbed when they flow through the silica capillary column and can be desorbed by liquid hexane followed by GC/MS analysis. The monolithic silica adsorbent is mechanically stable and no frits or other special structures are needed to retain them in place. In addition, owing to the smaller size of the capillary column, only a small volume of desorption solvent is needed. The present investigation demonstrates the satisfactory applicability of monolithic silica as a capillary adsorbent.     

Rapid concentration of organics from aqueous solutions through uncoated capillary columns: A new approach to purification and ultratrace analysis

Summary A new technique has been developed for the concentration of organics in aqueous solutions. Volumes greater than 100 ml can be utilized in this system, which previously could not have been done without a distillation or solvent extraction procedure. The method is based on the passage of the solution through uncoated capillary columns of various materials such as polyethylene, copper, aluminum, nickel, and many other metal and/or polymer columns of different dimensions. It is possible to achieve trace level analysis at the ppb to ppt level without the interferences inherent in other existing methods. The purification of solvents has been successfully demonstrated in this preliminary study, and will be discussed along with our suggestions for future investigations.Paper presented at the 21st Symposium on Advances in Chromatography, Oslo, Norway, June 3–6, 1985.     

气提浓缩仪分析水中痕量挥发性有机物研究

本文描述了气提浓缩仪的设计及操作程序用于对水中痕量挥发性有机物的测定。分析物被气提吸附于TenaxGC柱上,然后直接脱附到毛细管气相色谱柱上进行分析,并用FID或MS鉴定。本文除对色谱条件进行优化外,对气提时间和脱附温度等分析操作条件也进行了研究。检测下限为0.01-0.30PPb,峰面积检测精度优于6.9％,对16种化合物的回收率优于74％。     

Isolation,Concentration and Subsequent Analysis by Capillary Gas Chromatography of Trace Amounts of Organophosphorus Compounds from Aqueous Samples

Abstract

Trace amounts (ppb or less) of phosphorus containing compounds present in aqueous samples are adsorbed on XAD-4 and subsequently eluted by means of ethyl acetate. The solvent and the eluted compounds are evaporated and swept over a Tenax-GC tube. This gas stripping method traps the phosphorus containing compounds together with only a small amount of the solvent whereas the water entrapped in the XAD step is removed simultaneously. The compounds are desorbed from the Tenax-GC tube and injected into the gas chromatograph using the combination of thermal desorption, cold trapping and flash heating. The subsequent analysis is carried out on a capillary column and the compounds are detected by means of a flame photometric detector. The various steps of the analytical procedure are discussed, including the recoveries of the different compounds studied and some instrumental aspects.     

Comparison of different algorithms to calculate electrophoretic mobility of analytes as a function of binary solvent composition

Ten different mathematical models representing the electrophoretic mobility of analytes in capillary electrophoresis in mixed solvents of different composition have been compared using 32 experimental data sets. The solvents are binary mixtures of water-methanol, water-ethanol and methanol-ethanol, respectively. Mean percentage deviation (MPD), overall MPD (OMPD) and individual percentage deviation (IPD) have been considered as comparison criteria. The results showed that a reorganized solution model, namely the combined nearly ideal binary solvent/Redlich-Kister equation, is the most accurate model among other similar models concerning both correlation ability and prediction capability.     

Rapid determination of desorption efficiency, and analysis of solvent mixtures for occupational exposure studies

Summary An analytical procedure has been developed for simultaneous determination of solvent mixture vapors to enable evaluation of occupational exposure. To determine the desorption efficiency the volatile components of the solvent mixtures were generated from a glass tube filled with glass wool. This device is easy to prepare and use. These vapors were then collected in activated charcoal tubes and analyzed by capillary gas chromatography. The method was tested with a mixture of 22 solvents, including aliphatic and aromatic hydrocarbons, alcohols, ethers, esters, and ketones, all at low concentrations. All the components were detected. When a 99∶1 mixture of carbon disulfide-dimethylformamide was used for desorption the efficiency was>75% for most of the solvents.     

Determination of Airborne Nicotine by Automatic Two-Stage Thermal Desorption Gas Chromatography

Abstract

An automated two-stage thermal desorption technique has been developed for the determination of airborne nicotine. Pumped samples are collected on adsorbent tubes and analysed by capillary gas chromatography using flame ionisation detection. The preconcentration effect of the adsorbent compared to solvent trapping or solvent desorption methods permits shorter sampling times and precludes the need for a selective detector.

By use of a basic program all exposure volumes and component details are entered into a method run table and after analysis exposure levels are automatically calculated and printed in report form by the data handling system. Consequently a large throughput samples may be analysed automatically and efficiently with minimal analyst involvement or sample preparation.

The technique described was originally developed to sample airborne nicotine in workplace environments where tobacco is processed. Comparison between this technique and the standard NIOSH method for airborne nicotine is discussed.     

Selective reductive desorption of a SAM-coated gold electrode revealed using fluorescence microscopy

The reductive desorption of a self-assembled monolayer (SAM) of a fluorescent thiol molecule (BodipyC10SH) from Au was characterized using electrochemistry and epi-fluorescence microscopy. Molecular luminescence is quenched near a metal surface, so fluorescence was only observed for molecules reductively desorbed and then separated from the electrode surface. Fluorescence imaging showed that reductive desorption was selective, with desorption occurring from different regions of the Au electrode depending on the extent of the negative potential excursion. When desorbed, the molecules were sufficiently mobile, diffusing away from the electrode surface, thereby preventing oxidative readsorption. At sufficiently negative desorption potentials, all of the thiol was desorbed from the electrode surface, resulting in fluorescence at the air/solution interface. The selective removal of the thiol monolayer from distinct regions was correlated to features on the electrode surface and was explained through potential-dependent interfacial energies. This in situ electrofluorescence microscopy technique may be useful in sensor development.     

Absorption and desorption of organic liquids in elastic superhydrophobic silica aerogels

The experimental results of the studies on the absorption and desorption of organic liquids in elastic superhydrophobic silica aerogels, are reported. The elastic superhydrophobic aerogels were prepared using methyltrimethoxysilane (MTMS) precursor by a two-step sol-gel process followed by supercritical drying. Monolithic superhydrophobic silica aerogels were used as the absorbents. In all, four alkanes, three aromatic compounds, four alcohols and three oils were used. The absorption property of the aerogel was quantified by the mass and moles of the organic liquid absorbed by unit mass of the aerogel. The superhydrophobic aerogels showed a very high uptake capacity and high rate of uptake. The desorption of solvents and oils was studied by maintaining the as-absorbed aerogel samples at various temperatures and weighing them at regular time intervals until all the absorbed liquid got totally desorbed. This was verified by measuring the weights of the aerogel samples before and after desorption. The transmission electron micrograph observations showed that the aerogel structure was not much affected by the solvent absorption, while the oil absorption led to the shrinkage resulting in a dense structure after the desorption. In all the cases, the aerogels retained hydrophobicity and could be re-used as absorbents.     

Interactions of Pb(II) with particles of a polluted river

Pb(II) interactions with the surface of suspended matter from a polluted river was studied using differential pulse anodic stripping voltammetry (DPASV) technique. Three sampling sites were selected and studies have been done with samples collected in different times of the year (winter, autumn and summer). The values have been compared with those obtained in spring in the same conditions [Sci. Total Environ. 151 (1994) 101].Particles were separated by centrifugation and suspensions of the freeze-dried particles were titrated with Pb(II), being measured the labile metal fraction by DPASV. For comparison, suspensions of river water without any separation have also been titrated.Results show that surface metal complexes are inert, within the time scale of the analytical technique and desorbed organics from surfaces, form labile Pb(II) complexes in solution. For each sample it was determined the capacity for Pb complexation of particles and desorbed organics and the differential function has been estimated. Despite the heterogeneity of ligands, the systems interpreted in a discontinuous way, present one or two kinds of dominant ligands with Pb affinity.     

The Use of Automated Headspace Gas Chromatography for Determination of 1,1,1-Trichloroethane in Rat Blood and Brain Tissue

Abstract

1,1,1-trichloroethane in blood and brain tissue from rats which had been artificially ventilated with solvent (8000 ppm) was analysed by automated headspace gas chromatography using a fused silica capillary column. A given concentration of 1,1,1-trichloroethane in the brain could be correlated with a corresponding concentration in the blood; both the uptake and release of the solvent were quicker in blood than in brain. No volatile metabolites of the solvent were found. Automated headspace gas chromatographic analysis is a rapid and sensitive technique for the quantitative registration of volatile organic solvents, e.g. of industrial importance, in body fluids and tissues.     

Determination of volatile organics in gaseous phase using porous adsorbents

A novel procedure is developed for the quantitative determination of volatile organics in the gas phase over samples. Substances were extracted and preconcentrated from the gas phase on porous polymer adsorbents under the conditions of thermodynamic equilibrium, followed by back extraction from the adsorbent using organic solvents. The final monitoring was performed by capillary gas chromatography with an internal standard. The influence of adsorption time and the concentration of substances in an aqueous solution on the degree of extraction were also studied; linear correlations between the quantities of substances in the gas and aqueous phases were found. The method was used for the determination of volatile substances in the gas phase over liquid and solid matrixes of different origin.     

Solvent desorption of asphaltenes from solid surfaces

The main goal of this paper is to compare the ability of different organic solvents to desorb asphaltenes from stainless steel surfaces. The asphaltenes were extracted from a North Sea crude oil by precipitation. The organic solvents are characterized based on their Hansen solubility parameters (HSPs). The adsorption of asphaltenes was followed by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). The asphaltene desorption efficiency of the solvents tested varied between 20% and 70%, with pyridine as the most efficient solvent. Carbon disulfide was found to be a poor desorption solvent, indicating the importance of solvent polarity. A simple model based on the HSPs seemed to give a good quantitative explanation of experimental desorption experiments.     

In situ extraction/preconcentration of PCBs and PAHs from aqueous samples using polytetrafluoroethylene tubing

In situ extraction/preconcentration of organics from water samples was accomplished using polytetrafluoroethylene (PTFE) tubing. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were concentrated inside the tubing by flowing aqueous samples through it. The adsorbed PCBs and PAHs were then recovered by solvent desorption. The eluent was subsequently analyzed using gas chromatography with electron capture detection (GC-ECD) or gas chromatography with flame ionization detection (GC-FID). Multiple samples were simultaneously processed to concentrate organics onto several PTFE tubings. Analyses of seawater and surface microlayers using this technique demonstrated that organics in the surface microlayers were elevated with respect to those in the water column, consistent with previous findings.     

Acceleration of free release static coating of capillary columns by the presence of polar solvents in the coating solution – a theoretical study

The cause of an observed acceleration in the free release static coating process of a capillary when more polar solvents are added to alkanes as stationary phase solvents has been studied. By using a computer program, 9 of the relevant physical parameers were calculated in relation to the composition of the solvent hixtures. Curves of these parameters vs composition of the mixures were drawn. From the results it can be deduced that the change of these parameters with the increase of polar solvents in the solution, is probably insufficient to explain the drastic increase of the free release static coating speed. A physical model is proposed to calculate the depth of the meniscus around which sufficient heat can be transferred into the evaporating surface per unit time, to evaporate the solvent at a rate that the coating speed indicates. It is demonstrated that when pentane-acetone mixtures are used to coat a capillary, the depth of the meniscus indeed is greater than when pure pentane is used. The proposed model may lead to a better understanding of phenomena involved in the static coating process.     

Recent developments and applications of liquid phase microextraction in fruits and vegetables analysis

The sample preparation step has been identified as the bottleneck of analytical methodology in chemical analysis. Therefore, there is need for the development of cost‐effective, easy to operate, and environmentally friendly miniaturized sample preparation technique. The microextraction techniques combine extraction, isolation, concentration, and introduction of analytes into analytical instrument, to a single and uninterrupted step, and improve sample throughput. The use of liquid‐phase microextraction techniques for the analysis of pesticide residues in fruits and vegetables are discussed with the focus on the methodologies employed by different researchers and their analytical performances. Analytes are extracted using water‐immiscible solvents and are desorbed into gas chromatography, liquid chromatography, or capillary electrophoresis for identification and quantitation.     

Application of an automatic thermal desorption–gas chromatography–mass spectrometry system for the analysis of polycyclic aromatic hydrocarbons in airborne particulate matter

The application of the thermal desorption (TD) method coupled with gas chromatography–mass spectrometry (GC–MS) to the analysis of aerosol organics has been the focus of many studies in recent years. This technique overcomes the main drawbacks of the solvent extraction approach such as the use of large amounts of toxic organic solvents and long and laborious extraction processes. In this work, the application of an automatic TD–GC–MS instrument for the determination of particle-bound polycyclic aromatic hydrocarbons (PAHs) is evaluated. This device offers the advantage of allowing the analysis of either gaseous or particulate organics without any modification. Once the thermal desorption conditions for PAH extraction were optimised, the method was verified on NIST standard reference material (SRM) 1649a urban dust, showing good linearity, reproducibility and accuracy for all target PAHs. The method has been applied to PM10 and PM2.5 samples collected on quartz fibre filters with low volume samplers, demonstrating its capability to quantify PAHs when only a small amount of sample is available.