Richard G. Melcher

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.

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.

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.

Dynamic U-tube system for solid sorbent air sampling method development

The system consists of a U-shaped calcium chloride drying tube used as a flow chamber and sample container and having one side arm for an air inlet and another to hold the sorption tube, which contains carbon, silica gel, or another sorbent and leads to the pump. Good recoveries were obtained in tests at 85/sup 0/C with silica gel as sorbent and 0.2 to 10 ppM of naphthalene, 1-methylnaphthalene, or biphenyl, and at 25/sup 0/C with activated charcoal as sorbent and 0.2 to 18.0 ppM of benzene, toluene, ethylbenzene, styrene, or divinylbenzene. Thus, determinations can be made of the interaction of components, what constitutes breakthrough, what breakthrough is, and how much of a safety factor must be designed into a particular sampling program to prevent breakthrough during field sampling. The method was superior to other techniques for most applications, particularly for compounds which are normally either liquids of low volatility or solids. Diagrams, graph, and tables are included.

Collection and Ion Chromatographic Determination of Ammonia and Methylamines in Air

A method is described for the collection of ammonia (NH3), monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) from air and their subsequent determination by ion chromatography. Samples are collected with 800-mg silica gel sampling tubes at a flow rate of 1 L/min for 10 minutes or at 100 mL/min for up to 7.5 hours. Samples collected with sulfuric acid-treated tubes can be stored at room temperature for at least 21 days with no loss in recovery. Untreated samples can be stored in a refrigerator up to 32 days. The method has been validated from 2 to 50 ppm v/v when a 10 L air sample is taken. No loss in recovery was observed when sampling up to 23 L of air at 100% relative humidity. The recovery and total precision (95% confidence level) for NH3, MMA, DMA, and TMA were 91 +/- 12.5%, 93 +/- 10.3%, 92 +/- 9.6% and 84 +/- 17.6%, respectively.

Collection of Ethanolamines in Air and Determination by Mobile Phase Ion Chromatography

A method is described for the collection and determination of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) in air. Samples were collected by pulling air through a glass tube containing alumina, cleaned especially to remove interfering inorganic ions. The ethanolamines were desorbed with water and determined by Mobile Phase Ion Chromatography (MPIC). The recovery and total relative precision for MEA, DEA and TEA – all collected from air at a flow rate of 100 mL/min for 7 hr – was 93.1±17%, 92.7±15% and 89.4±21%, respectively (95% confidence level). The method was validated for all three compounds from approximately the limit of detection (3 × noise) to ten times the limit of detection. Based on a sample size of 42 L, MEA was validated over the range from 0.12 to 3.0 ppm v/v (TLV®=3), DEA over the range from 0.25 to 3.3 ppm v/v (TLV=3) and TEA from 0.31 to 3.7 ppm v/v (no TLV assigned). No effect on recovery was observed when sampling at high humidity or on storage of the samples f...

Reactive adsorbent derivative collection and gas chromatographic determination of chloromethyl methyl ether in air

A method has been developed and validated for the derivatization and collection of chloromethyl methyl ether (CMME) on a reactant-coated solid adsorbent tube. Following sampling, the CMME derivative is desorbed into methanol, cleaned up with aqueous KOH, extracted into hexane, and analyzed by gas chromatography with electron capture detection. Air containing the CMME is pulled through an air sampling tube containing 1.5% potassium 2,4,6-trichlorophenate on modified 120/140 mesh GLC-110 as the adsorbent. A derivative is formed by the reaction: The procedure is designed for industrial hygiene monitoring to give an accurate 4-hour time-weighted-average of the exposure level. Yields were found to be 56±10% (2σ) while recoveries independent of yield were 96±6% (2σ) for CMME concentrations in the range of 6 ppb (v/v) to 900 ppb (v/v) in air. Breakthrough concentrations, humidity and storage effects and other parameters were also investigated.

Oxygen Depletion in Corroded Steel Vessels

Although steel treated with MgCl2 has shown high corrosion rates when in a warm humid atmosphere, the rapid and extensive oxygen depletion observed in a MgCl2 evaporator was much greater than expected. A plant test of a MgCl2 evaporator showed the oxygen content decreased from normal (20.95%) to approximately 1% in 24 hr. The reason for this unexpected O2 depletion was investigated in the laboratory by enclosing test samples in a simulation chamber and monitoring O2 and N2 with a mass spectrometer interfaced to the chamber with a silicone hollow fiber membrane probe. The tests show that the surface scale (magnetite) increases O2 depletion by more than ten fold over that of clean metal. The tests also show that the formation of Fe2O3 is not a factor in the first 24 hr but that the formation of an iron-magnesium compound, Iowaite [Mg4Fe(OH)8OCl·XH2O], which contains a high percentage of oxygen, was observed in the exposed samples. The study has shown that the corrosion process during equipment downtime can ...

Concentration and determination of the propylene glycol butyl ether esters of 2,4-dichlorophenoxyacetic acid (PGBE 2,4-D) in air

A method has been developed and validated for the determination of airborne propylene glycol butyl ether ester and the dipropylene glycol butyl ether ester of 2,4-dichlorophenoxyacetic acid. The method is designed to collect samples in the breathing zone of workers for 4 hours at 150 mL/min. using a tube containing 750 mg of Amberlite XAD-2 resin and a portable pump. Recoveries of 85.2% and 81.4% were obtained for the two esters over a range of 0.67 and 13.3 mg/m3 by desorption wih hexane. The extracts were analyzed by electron capture gas chromatography using a highly efficient and inert bonded Carbowax 20-M column packing. The recovery was not affected by 80% relative humidity or refrigerated storage for two weeks. Some loss in recovery was observed for the 0.67 mg/m3 level when samples were stored at room temperature for two weeks. The overall precision of the method for the two esters is +/- 17% and +/- 16% at the 95% confidence level.

Improved methodology for field validation of industrial hygiene monitoring methods

During the development and validation of industrial hygiene monitoring methods in the laboratory, various parameters of collection, storage, and analysis are studied. It is not feasible, however, to study all the environmental variables in the laboratory, so field validation is necessary to detect problems which are specific to the actual work site. A statistical procedure to evaluate the field validation experiment is described together with the methodology necessary to perform these experiments and the equipment to facilitate these experiments. These procedures are demonstrated in an experiment measuring acrylonitrile in the workplace.