Permeation Tubes Research Articles

Permeation characteristics of organic vapors in silicone rubber tubing

Since silicone rubber exhibits sufficient inertness, it can be used as a permeation device to generate known standard atmospheres of organic vapors. The permeation characteristics of organic vapors through silicone permeation tubes are examined by their transport phenomena under saturation steady state conditions. The permeation rate is a function of solubility and diffusion rate. The solubilities of organic vapors in silicone rubber can be estimated by the Flory-Huggins relationship with a single value of the interactive parameter (χ). The integral diffusion coefficient and the activation energy can be deduced from experimental permeation rate data and estimated solubility data. Several industrial organic vapors are studied at various concentrations, temperatures, and tube-wall thicknesses. The high permeation rate of organic vapors through silicone rubber is a consequence of the low energy for permeation.

Determination of CHFCl2(CFC21) in the troposphere

Abstract In the frame of the controversy about stratospheric ozone depletion by halocarbons, it has been hypothesized that CFC21, which has no industrial use, could be a decomposition product of CFCl1. However the quantitative analysis of this compound is quite difficult because of: 1. its low concentration 2. difficult GC separation fom other halocarbons and possible interferences and sample contamination. This problem has been solved by using analytical techniques based on the following points: 1. Sampling is carried out by trapping air on Carbopack B (graphitized carbon black) at low temperature and injecting via the heat stripping technique (1). This allows sampling of lagre air volume (up to 30 liters). 2. Analysis is performed by GC-ECD and GC-MS. An extremely selective GC column is used which allows the seperation of most halocarbons possibly present in the atmoshpere (1). The mass-spectrometer, used in the multiple ion monitoring mode (M.I.D.) (2), offers a very reliable method for the qualitative and quantitative determination of halocarbons (3). 3. Calibration is carried out by means of permeation tubes that allow to obtain the most reliable primary standard because of the accuracies of gravimetric measurements (4). Samples collected at different locations have been analyzed. Depending on metereological conditions, latitude and seasons, concentrations of CFC21 much larger than expected have been found. The regularities connected to the appearances and disapperances of CFC21 are such that the need for more extensive measurements are imperative to ascertain wether the hypotesis made about its origin can be feasible or not.

A Gas Exposure System for Insects

A system was developed for chronic low level exposure of insects to air contaminants. The system is economical, compact, and reliable. It incorporates the use of permeation tubes which is a new concept in entomological research to date. The system is useful in long term, constant temperature, low level fumigation studies involving a variety of gases.

Calibration of a permeation tube and a diffusion tube with an electrobalance.

An electrobalance equipped with a hang down assembly was used to calibrate a permeation rate of vinyl chloride in a permeation tube and a diffusion rate of organic solvent in a diffusion tube. The permeation rate obtained by the electro-balance coincided fairly with that measured by means of a chemical balance. Gas chromatographic analysis of organic solvent vapor in the dynamic mixture prepared by the diffusion tube technique showed that diffusion rate obtained by the elec-trobalance was practically close to that obtained by the gas chromatography. Calculated diffusion rate was also in good coincidence with the value observed by the electrobalance. Several advantages were presented to calibrate the permeation tube and the diffusion tube by the electrobalance.

Reaction of Copper and Copper Oxide with H 2 S

The lack of sulfidation of copper in indoor atmospheric corrosion has been attributed to the formation of copper oxide on copper, i.e., the oxide which forms on the copper surface initially inhibits the growth of corrosion (sulfide films) on the surface. A permeation tube apparatus has been constructed with a quartz crystal microbalance (sensitivity ∼10−8g) to elucidate the reaction of copper and copper oxide with . The film composition was measured with ESCA and Auger spectroscopy and the film thickness was measured with the quartz crystal microbalance to avoid the ambiguity of thickness estimation from sputter rate measurements in depth profiling. Results indicate that copper oxides grown in air (several hundred Å thick) provide good protection against at low relative humidities, but little protection at high relative humidities. Oxides grown in pure oxygen provide more protection, but still tarnish rapidly at higher relative humidities.

Sulfur trioxide permeation tube for calibration of sulfuric acid measurement methods

Sulfur trioxide permeation tubes were prepared and calibrated for use in evaluating the effectiveness of flue gas sampling equipment designed for determination of sulfuric acid in fossil fueled combustion sources. By diluting and passing the vapors from the liquid SO/sub 3/ permeation tube through a midget bubbler, the resulting sulfuric acid aerosol was efficiently collected by a quartz fiber filter and titrated after washing. Over the 45 to 80/sup 0/C temperature range, the SO/sub 3/ permeation rate varied exponentially from about 2 to 35 ..mu..L/min with a repeatability of +-8%. At a constant temperature, the repeatability was better than +-3%. The SO/sub 3/ permeation tube had a projected refrigerated storage lifetime of 30 years, an operating lifetime of 1 month at 65/sup 0/C or 1 year at 35/sup 0/C, and a permeation rate suitable for calibrating H/sub 2/SO/sub 4/ flue gas monitors. As a generator for simulating atmospheric H/sub 2/SO/sub 4/ aerosol concentrations, a permeation wafer device emitting SO/sub 3/ at 0.1 ..mu..L/min was expected to have a 10-year operating lifetime at 65/sup 0/C. 3 figures, 3 tables.

A new method for the generation of standard atmospheres of organo isocyanates

A new and versatile method for the generation of standard atmospheres of several organo isocyanates based on permeation technique has been developed. Several membranes were screened for integrity, compatibility and permeability of these isocyanates. Silicone membrane was found to be the best membrane for the construction of permeation devices. Two types of permeation are described: liquid phase and gas phase. The liquid phase permeation tubes are recommended for generation of high concentrations (ppm) and gas phase permeation is preferred for generation of atmospheres with low concentrations (ppb). Several simple designs for construction of permeation devices are described. The permeation of isocynates were evaluated gravimetrically and were shown to be constant, provided the temperature and the flow rate of air over the permeation tube are maintained constant.

Measurement of atmospheric vinyl chloride.

Methods for atmospheric vinyl chloride measurement have been reviewed. The lowest detection limits and most specific measurement are achieved by scrubbing atmospheric samples with activated charcoal, desorbing the vinyl chloride, and assaying it by gas chromatography (GC). NIOSH currently recommends collecting samples using tubes packed with 150 mg of coconut shell charcoal, desorbing with carbon disulfide, and analyzing by GC equipped with flame-ionization detection (FID); the method is capable of detecting less than 1 ppm vinyl chloride and has an apparent recovery of abo the ppb level with no loss of accuracy or precision. Some field methods, such as infrared analysis and conductivity measurement, are capable of detecting 1 ppm or lower but are subject to interferences by other contaminants; th-y could be useful for evaluating sources of vinyl chloride leaks and for continuous monitoring. Permeation tubes are superior to gravimetric or volumetric methods for generating atmospheres of known vinyl chloride concentration.

Preparation of permeation tubes containing 35SO 2

Preparation of permeation tubes containing 35SO 2

Preparation of refillable permeation tubes

Preparation of refillable permeation tubes

PREPARATION OF DYNAMIC MIXTURE OF VINYL CHLORIDE AND AIR BY PERMEATION TUBE

A method to construct a permeation tube of vinyl chloride was described. The constructed tube was held in a water jacket, temperature of which was controlled by circulating water from a thermoregulated water bath, and a clean air diluent flew through the jacket to prepare air-gas mixture stream of known concentration. The concentration of vinyl chloride in the stream was determined gas chromato-graphically and a fairly good linearity was observed between the calculated con-centration and chromatographic peak height. An apparent activation energy of permeation was calculated from temperature dependency of permeation rate.

Advances in assembling permeation tubes

Advances in assembling permeation tubes

Generation of accurate halocarbon primary standards with permeation tubes

Generation of accurate halocarbon primary standards with permeation tubes

Determination of hydrogen sulfide, carbonyl sulfide, carbon disulfide, and sulfur dioxide in gases and hydrocarbon streams by gas chromatography/flame photometric detection

The application of a gas chromatograph/flame photometric technique to the separation and measurement of four compounds, H/sub 2/S, COS, CS/sub 2/, and SO/sub 2/ in inert gases and hydrocarbon streams, is described. Three columns were necessary to achieve separation of the sulfur compounds from each other and from interferences. These procedures are applicable up to the 50-ppM level. Higher levels are measured after dilution. The lower detection limits in mole ppM are: COS and CS/sub 2/, 0.2; SO/sub 2/, 0.4; and H/sub 2/S, 0.8. The standard deviation for H/sub 2/S at 6.70 mole ppM level is 0.23 and for COS at 3.97 mole ppM is 0.06. Although not measured, CS/sub 2/ is expected to behave like COS and SO/sub 2/ like H/sub 2/S. The accuracy of the blends prepared by means of permeation tubes is estimated to be 3% of the amount present.

Preparation of Sulfur Dioxide with Constant Low Concentration from the pH Controlled Sodium Hydrogensulfite Solution

A new method was developed for the generation of sulfur dioxide with constant low concentration (from 10 to 0.01 ppm). This method is based on the generation of sulfur dioxide from an aqueous solution of sodium hydrogensulfite with appropriate buffer agents. The pH of the solution was controlled by adding the buffer agents to it. Sulfur dioxide was generated by passing air through the surface of the solution. The generated gas was diluted with air of constant stream, passed through a purification bed. The concentration of the gas depended on pH, concentration, and temperature of the sodium hydrogensulfite solution. The gas generation from the solution began at pH 7.0, and generation of a large amount of gas occurred at pH 4. O. A logarithmic relationship between concentration of the solution and that of the generated gas in the air stream was found in a concentration range of sodium hydrogensulfite solution from 5 X 10 to 5x 1O2- pglml. The temperature dependence on this method was much less than that on the permeation tube method and the variation of concentration of the generated gas with temperature was 0.O2- ppm/°C at 20, ---30°C, 0.56 ppm of SOO. The concentration of the generated gas reached a constant value within about 40 min after starting of the air flow, and it remained constant at least during 6 hours. The range of variation of the generated gas was 2% at 0.56 ppm.

Development of calibration systems for measuring total reduced sulfur and sulfur dioxide in ambient concentrations in the parts per billion range

A calibration system tested by the Pulp and Paper Research Institute of Canada for monitoring total reduced sulfur and SO/sub 2/ in the 0.1 to 100 ppB concentration range uses permeation tubes with an exponential dilution flask, a flame photometric detector, and a solid NaHCO/sub 3/ filter to separate SO/sub 2/ from reduced sulfur compounds. Results show that the system works effectively to achieve continuous calibration and monitoring in this concentration range.

Use of permeation tubes for calibration of vinyl chloride analyses

Use of permeation tubes for calibration of vinyl chloride analyses

Preparation of vinyl chloride standards using a permeation tube

Vinyl chloride permeation tubes have been utilized to provide a convenient and accurate standardization procedure for charcoal tube monitoring of atmospheric vinyl chloride. The procedure circumvents the need of determining charcoal desorption efficiencies and eliminates the handling of free vinyl chloride in the laboratory preparation of vinyl chloride standards.

Trace analysis for chlorinated hydrocarbons in air by quantitative combustion and coulometric chloride determination: Application to standardization of vinyl chloride permeation tubes

Methods for high-temperature combustion of vinyl chloride in air were studied theoretically and two types of gas mixtures were found to give 100% conversion into HCl. The chloride was determined by coulometric titration with silver, in 70% acetic acid. Good agreement between theoretical and experimental results was obtained. Permeation rates of vinyl chloride from fluorinated ethylene propylene permeation tubes were determined gravimetrically and with the coulometric method developed. The standard deviations of the methods were 0.002 and 0.001 μg min respectively for permeation rates of 0.5 μg min when the temperature was controlled to ± 0.02°. The coulometric mean value was 99.9% of the gravimetric mean; 1 ppm of vinyl chloride in air could be determined coulometrically with a standard deviation of about 0.002 ppm.

Dynamic Calibrations of Saltzman Type Analyzers Using NO2 in Air Mixtures

This paper describes how dynamic dilution systems can be used I prepare ambient levels of NO2 in air for calibration of Saltzms type continuous analyzers. Permeation tubes may in the future b more applicable, but for the present these are not in general use. A number of field calibrations were made on regular station an; lyzers using a special portable field calibrator which showed th; each instrument has a unique Saltzman factor. These were four to vary all the way from 70 to 90.