User`s guide

Sampling Techniques

321

Introduction

Two general methods of sampling are used for ATD/TD analyses i.e.

Trapping Volatiles from the Vapor Phase and Direct Sampling.

With direct sampling methods you place a known quantity of the

sample into the tube. Alternatively, you can trap volatiles on the

tube. Various sampling methods are discussed in this chapter. For

more detailed information you may want to obtain some of the listed

reference material (see later in this chapter and in Appendix C).

Table 23 Thermal Desorption Sampling Techniques

Theory of Diffusive Monitoring

Diffusive monitoring is a simple and convenient air sampling

procedure. The small, light, diffusive samplers are preferred by

workers during personal monitoring studies and, using them

eliminates the risk of an individual changing working practices

simply because he/she has to carry a sampling pump.

To be effective, diffusive monitors must be capable of maintaining

the following conditions during the sampling process:

• ambient concentration of the component(s) of interest at the

surface of the monitor

• zero concentration of the component(s) at the surface of the

adsorbent or reactive material

• a linear concentration (diffusion) gradient between the two.

Trapping Volatiles from the

Vapor Phase

Direct Sampling

Diffusive Monitoring

(stainless steel tubes only)

Liquids and Emulsions

Pumped Sampling

(Air Monitoring)

Resins and Ointments

Purge and Trap Solid Sampling

Soil Probes