Module Monitoring and Measuring Human External Exposure Integrated

Module Monitoring and Measuring Human (External) Exposure: Integrated Monitoring of Airborne Organic Gases and Vapors Using Absorbents Michael Bisesi, Ph. D, REHS, CIH Senior Assoc. Dean, Academic Affairs Director, Center for Public Health Practice Chair & Assoc. Professor, Environmental Health Sciences Exposure Science Monitoring Techniques

Module: Integrated Monitoring of Airborne Inorganic & Organic Gases & Vapors Using Absorbents Objectives: § Name, identify, and assemble the components of the sampling train § Name, identify, and assemble the components of the calibration train § Summarize principles of integrated sampling and analysis of air for airborne organic gases and vapors using liquid absorbents § Perform applicable calculations References: § Bisesi, M. (2003, 2 nd ed. ). Bisesi & Kohn’s Industrial Hygiene Evaluation Methods. CRC press/Taylor & Francis Publishers. Boca Raton, FL. § CDC/NIOSH Manual of Analytical Methods. http: //www. cdc. gov/niosh/docs/2003 -154/

Polar Gases/Vapors § Relatively water-soluble § Organic solvents such as alcohols http: //www. aceorganicchem. com/Elite/organic-chem-15 -organic-solvents-likes-dissolve-likes/

Polar Gases/Vapors

Absorbents § Solid adsorbent media are preferred for conducting integrated monitoring of gases and vapors § However, some compounds are not collected efficiently using these media § Solid adsorbents (i. e. activated charcoal and silica gel) are used most frequently to collect relatively water insoluble and nonreactive gases or vapors § Liquid absorbents, are used for relatively more soluble and reactive gases and vapors § Makes them an alternative collection media for organic gases and vapors, as well as, some inorganic gases and mists

Absorbents § Adsorption- gas or vapor molecules bond to the surface of a solid medium § Absorption- dissolution of molecules of gases and vapors into a liquid medium § The liquid absorbents are contained in specialized sampling devices during monitoring. § Purpose of the sampling devices is to enhance aeration of the liquid absorbent with the sampled air so that increased surface area and mixing is available. § Increased contact between the gas and vapor molecules and the liquid absorbent enhances the efficiency of collection of the contaminant.

Midget Impingers § Midget impingers are columnar glass devices that provide a reservoir for liquid absorption reagents § Inserted in the reservoir is a hollow glass inlet tube open at each end and tapered at the bottom. § When the reservoir is filled with 10 -20 ml of liquid medium, the tapered end of the tube is immersed in the fluid § The tube serves as a conduit for the air to enter the impinger and mix with and dissolve into the liquid absorbent

Midget Bubblers § Designed very much like impingers, except that the glass inlet tube is not tapered. § The end of the hollow tube in a midget bubbler is a porous piece of glass with a sponge‑like appearance. § This structure is called a "frit" and is immersed in the liquid absorbent. § When air is drawn through the fritted glass at the end of the tube, smaller and more bubbles are generated relative to the midget impinger. § The actual size of the bubbles depends on the nature of the liquid and the diameter of the frit pores.

Midget Bubblers (cont’d) § Frits range from “fine” to “extra coarse” § Depending on the number of pores per unit area § The more coarse the frit, the more rapid the flow § The small bubbles generated allow increased surface area for contact and mixing of gases and vapors with the absorbent § can result in increased collection efficiency § Midget bubblers are generally used to collect less reactive gases or vapors that might not be collected as efficiently using midget impingers

Spills § Major disadvantage of using midget impingers and bubblers is that the liquid absorbent can spill and/or be pulled into the air sampling pump. § Important that the impingers be positioned vertically during monitoring § Holster devices can be used to assist in maintaining the impinger in a vertical position § “Spill-proof” devices are available § Spill trap can be used, such as an empty impinger in line between the pump and the impinger that contains the liquid medium

Volatile Liquid Absorbents § It is possible for volatile liquid absorbents to generate vapors which can be pulled into the pump § When these types of reagents are used a vapor trap, such as a charcoal tube for non-polar or a silica gel tube for polar solvents, in line between the pump and impinger

Sample Collection § The air is actively drawn into the impinger or bubbler by means of an air sampling pump that is connected via a flexible hose to a glass outlet tube that projects horizontally from the top of the device. § As the air is pumped from the atmosphere and into and through the vertical glass inlet tube, bubbles are formed as the air enters the liquid medium. § The combination of the bubbles and mixing facilitates collection or trapping of the gas or vapor molecules in the liquid absorbent.

Calibration Train: Organic Vapors § High- or Multi-flow pump § Flexible Tygon tubing § Glass midget impinger or bubbler containing liquid absorbent § Frictionless bubble tube (or equivalent)

Sampling Train: Organic Vapors § High- or multi-flow pump § Flexible Tygon tubing § Glass midget impinger or bubbler containing liquid absorbent

Impingers and Bubblers

Sampling Train: Organic Vapors

Analysis: Organic Vapors § “Spectrophotometric” § UV/Vis Spectrophotometer

UV/Vis Spectrophotometery

UV/Vis Spectrophotometery (cont. )

UV/Vis Spectrophotometery (cont. )

Addendum to Modules: Alternative Method for Integrated Monitoring of Airborne Organic & Inorganic Gases and Vapors § Passive Diffusion Dosimeters § Do not need active flow pump § Simply attach media to area or person being monitored § Submit for laboratory analysis (some have direct-read capabilities) § Still being evaluated for accuracy and precision relative to conventional active sampling methods

Alternative: Passive Dosimeters § Alternative sampling devices called passive dosimeters have been developed and are continually being perfected for monitoring organic gases that have been traditional sampled using glass tubes containing charcoal and silica gel adsorbents. § The devices are referred to as "passive" dosimeters since they due

Alternative: Passive Dosimeters § Instead, the devices are designed to enhance the passive diffusion of airborne vapors into the dosimeter where the contaminant adsorbs to a solid sorbent, typically activated charcoal. § The rate of diffusion is controlled by the dimensions of the collection device, the diffusion coefficient of the

Examples: Passive Dosimeters

Passive Dosimeter

Bulk Sampling

REMEMBER: Some Major Questions to Answer Pre-Sampling: § § Sampling Train, including media? Calibration? Flow Rate? Sampling Duration (Min/Max Sample Volume)? § Number of Samples? § Number of Blanks? § Media Handling and Storage: Pre- and Post-Sampling?

ALWAYS! § Check the Applicable Method § NIOSH § OSHA § etc. § Check w/ the Analytical Laboratory § Document Calibration, Field, and Laboratory Notes, Observations, Data. . .