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Biomedical subjects

R G Melcher

Publications and source records attributed to R G Melcher.

8 recordsLinked to original sources
PubMed1986

Development and validation of personal monitoring methods for low levels of acrylonitrile in workplace atmosphere: I. Test atmosphere generation and solvent desorption methods.

The purpose of this study was to optimize monitoring methods and to investigate new technology for the determination of low levels of acrylonitrile (0.05 to 5 ppm) in workplace atmospheres. In the first phase of the study, a dynamic atmosphere generation system was developed to produce low levels of acrylonitrile in simulated workplace atmospheres. Various potential sorbents were investigated in the second phase, and the candidate methods were compared in a laboratory validation study over a concentration range from 0.05 to 5 ppm acrylonitrile in the presence of potential interferences and under relative humidity conditions from 30% to 95% RH. A collection tube containing 600 mg Pittsburgh coconut base charcoal was found to be the optimum tube for sampling for a full 8-hr shift. No breakthrough was observed over the concentrations and humidities tested. The recovery was 91.3% with a total relative precision of +/- 21% over the test range, and the recovery was not affected by storage for up to five weeks.

Acrylonitrile↗
PubMed1986

Development and validation of personal monitoring methods for low levels of acrylonitrile in workplace atmosphere: II. Thermal desorption and field validation.

Thermal desorption is a more sensitive alternative to solvent desorption for the determination of acrylonitrile in air. A dual-bed collection tube (Tenax GC and Carbosieve B) was developed for collecting and concentrating low levels of acrylonitrile. Two thermal desorption techniques were evaluated for the recovery of acrylonitrile collected on the dual-bed tubes over a concentration range from 0.05 to 5 ppm. A commercially-available system, the Century Programmable Thermal Desorption Unit, was easy to operate, allowed for multiple injections of the sample and had a recovery of 82 +/- 12% (RSD). Samples were stored for up to two months without affecting the recovery and there was not an observable effect from humidity or from the presence of other organic compounds. This system was found to have limitations at acrylonitrile concentrations above 1 ppm. A field validation study tested the sampling and analytical methods developed for monitoring low levels of acrylonitrile in the workplace. Three methods employing Pittsburgh Coconut-Base activated charcoal, Ambersorb XE-348 and Tenax-GC and Carbosieve B sampling mediums were validated for concentrations ranging from 0.05 to 5 ppm and confirmed in the field from 0.02 to 3 ppm in tests conducted at plant sites. These field studies were run over varying humidity and temperature conditions. The overall absolute recoveries and relative standard deviations found for these methods found during the field trials are 90 +/- 18% for charcoal; 85 +/- 11% for Ambersorb XE-348; and 90 +/- 19% for the Century dual-bed sorbent. These values were in quite good agreement with the 91 +/- 10%, 88 +/- 8%, and 82 +/- 12% determined in laboratory studies.

Acrylonitrile↗
PubMed1979

Simultaneous determination of polar and non-polar solvents in air using a two-phase desorption from charcoal.

A gas chromatographic procedure is described which is capable of measuring both polar and non-polar organic solvents present simultaneously in the work environment at concentrations between 1/100 and 1 times the Threshold Limit Values (TLV). Airborne organics are collected on a single activated charcoal tube for periods of 3 to 6 hours and desorbed with a two-phase (water/carbon disulfide) desorption mixture. Organic and aqueous phases are analyzed separately on the same gas chromatographic column packed with Oronite NIW on Carbopack B. Recoveries were determined for fifteen common solvents. Most recoveries were greater than 90% with all coefficients of variation being less than +/- 10%. Breakthrough was observed only when solvents were present at very high concentrations. Examples of field sampling are also presented. This procedure is generally applicable for monitoring complex mixtures of volatile organic compounds in air. Advantages include excellent recoveries for polar solvents such as acetone and ethanol, utilization of common analytical instrumentation under a single set of operating conditions and compatibility with TWA personnel monitoring methodology.

Air↗
PubMed1978

Phase equilibrium method for determination of desorption efficiencies.

The principle of phase equilibrium is applied to the determination of desorption efficiencies of organic compounds collected on activated charcoal. The method depends on the existance of a true equilibrium distribution between the adsorbed and solution phases of organics in the desorption solvent--adsorbent matrix. Improved and more consistant desorption efficiencies are obtained by considering the effects of variations in the adsorbent--solvent ratio and equilibrium temperature at time of analysis. The technique may also provide early detection of interaction or reaction of the sorbate on the adsorbent surface.

Adsorption↗
PubMed1978

Criteria for the evaluation of methods for the collection of organic pollutants in air using solid sorbents.

A small tube containing a solid sorbent is convenient to use for collecting and concentrating trace organics in ambient air and worker breathing zones. Many techniques for air sampling with solid sorbents, especially for the long term eight hour sample, are relatively new. It is necessary to have criteria to judge methods utilizing these techniques and to establish guidelines which are accurate and practical. Parameters which affect collection and recovery and information necessary to define, develop and evaluate a sampling method are discussed. Progressive steps for the development and validation of air sampling methods are recommended.

Adsorption↗