Solutions Of Volatile Organic Compounds Research Articles

Principles and Calibration of Solid Phase Microextraction Fibre (Passive Sampler) for Measurements of Airflow and Air Infiltration in Dwellings

Tracer gas techniques have been the most appropriate experimental method of determining airflows and ventilation rates in houses. However, current trends to reduce greenhouse gas effects have prompted the need for alternative techniques, such as passive sampling. In this research passive sampling techniques have been used to demonstrate the potential to fulfil these requirements by using solutions of volatile organic compounds (VOCs) and solid phase microextraction (SPME) fibres. These passive sampling techniques have been calibrated against tracer gas decay techniques and measurements from a standard orifice plate. Two constant sources of volatile organic compounds were diffused into two sections of a humidity chamber and sampled using SPME fibres. From a total of four SPME fibres (two in each section), reproducible results were obtained. Emission rates and air movement from one section to the other were predicted using developed algorithms. Comparison of the SPME fibre technique with that of the tracer gas technique and measurements from an orifice plate showed similar results with good precision and accuracy. With these fibres, infiltration rates can be measured over grab samples in a time weighted averaged period lasting from 10 minutes up to several days.

Effect of PBPK Model Structure on Interpretation of In Vivo Human Aqueous Dermal Exposure Trials

Multiple research teams have reported data from in vivo human trials in which breath was monitored during and after whole-body or partial immersion in aqueous solutions of volatile organic compounds. Estimation of total dermal absorption from exhaled breath measurements requires modeling, a task to which physiologically based pharmacokinetic (PBPK) models have often been applied. In the context of PBPK models, the exposed skin compartment can be modeled in many different ways. To demonstrate potential effects of alternative skin models on overall PBPK model performance, alternative models of skin have been incorporated in a PBPK model used to predict chloroform in breath during and after immersion in aqueous solution. The models investigated include treatment of skin as both a homogeneous phase and as a membrane in which concentration varies with depth. Model predictions are compared with in vivo human experimental results reported in the prior literature. In the example chosen, the common practice of modeling skin as a homogenous phase leads to prediction of more rapid initial uptake and lower cumulative uptake than does modeling skin as a membrane. Numerical estimates of the permeability coefficient are shown to be dependent upon skin model form and temperature of the aqueous solution.

Concentration polarization, separation factor, and Peclet number in membrane processes

Concentration polarization affects almost all the membrane separation processes and can be the cause of a substantial reduction in the separation factor and flux. A generalized equation relating the modified Peclet number to the concentration polarization occurring in the boundary layer is proposed and shown applicable to the majority of membrane separation processes like gas separations, reverse osmosis, ultrafiltration, pervaporation, and dissolved gas permeation in liquid. The membrane permeability, separation factor (or solute rejection), membrane thickness, boundary layer mass transfer coefficient, and Henry's law coefficient are the factors that determine the extent of polarization. An analysis is presented to offer a clean division of the hydrodynamic effect from the pure membrane property for membrane separation processes of liquid phases. Also the effect of membrane thickness on polarization is discussed. An attempt has been made to reconcile the different approaches taken for different membrane processes in the literature. Experimental data from widely different sources illustrate and confirm the present theory for pervaporative separation of dilute solutions of volatile organic compounds, dissolved gas permeation, and ultrafiltration of proteins and carbowax. Specific suggestions are made to obtain independent experimental measurements of the Peclet number and polarization index in terms of measurable quantities like the actual and intrinsic separation factors.

Direct Determination of Organic Compounds in Water at Parts-per-Quadrillion Levels by Membrane Introduction Mass Spectrometry

Parts-per-quadrillion level detection of toluene and trans-1,2-dichloroethene in water has been achieved on-line, without preconcentration, by employing selective ionization in conjunction with membrane introduction ion trap mass spectrometry. The stored wave form inverse Fourier transform technique is used to create broad-band wave forms, notched at the resonance frequencies of analyte ions of interest. A series of such pulses is applied during ionization to eject unwanted ions and store only analyte ions. This capability is used over long ionization times to obtain extraordinarily low detection limits for aqueous solutions of volatile organic compounds, introduced into the ion trap using a silicone membrane located within in a commercially available capillary membrane inlet system

Analysis of Trace Levels of Volatile Organic Contaminants in Municipal Drinking Water by Glass Capillary Gas Chromatography Using Simultaneous Flame Ionization and Electron Capture Detection

Abstract A glass capillary gas chromatographic system using simultaneous flame ionization (FID) and electron capture (ECD) detection has been employed for the analysis of trace volatile organic pollutants in a municipal drinking water supply. The use of dual detectors with glass capillary columns allows resolution and detection of both halogenated and non-halogenated compounds simultaneously at less than microgram per liter (ppb) concentrations. By using diethyl ether as a solvent in preparing standard solutions of volatile organic compounds, standardization is made more accurate due to a reduction in solvent masking of early eluting peaks of interest. Additionally, ether shows promise for use in an internal standard method for quantification of VOA. These techniques were found to alleviate problems previously encountered in the analysis of purgeable organics and are described.

Application of gas chromatographic headspace analysis to the characterization of chemical equilibria in solutions

The possibility is considered of using headspace analysis in studies of chemical equilibria in solutions of volatile organic compounds. The main theoretical relationships for the determination of the constants of X + Y ⇄ XY type equilibria by the gas chromatographic analysis of equilibrated vapour above a solution are derived. New methods are proposed and have been checked experimentally for the measurement of the ionization constants of volatile organic compounds, and of the stability constants of metal complexes with unsaturated and aromatic hydrocarbons.

Method for Preparing Sterile Solutions of Volatile Organic Compounds

Method for Preparing Sterile Solutions of Volatile Organic Compounds