ABSTRACT
Gas and vapor mixtures with air can be produced by a wide variety of methods. Each situation must be dealt with separately depending on the experimental circumstances. Before a scientist devises any system, he must decide what concentrations, volumes, flow rates, accuracies, and equilibrium times are required. In addition, he must determine if his material resources and budget are sufficient to fabricate a system to meet his needs. The summary presented in Table 1.1 can be used as a guide to acquaint the reader with the basic systems discussed in this book. Once the proper system requirements are determined, the reader can better identify which chapter and section will best fit the immediate experimental needs. Characteristics of Methods for Producing Gas and Vapor Mixtures
Methods
Usual Range of Concentration
Volume of Test Mixture (L)
Average Best Accuracy (%)
Operating Pressure (atm)
Degree of Wall Loss
Static systems
Single vessel
10 ppm to 5%
10% of vessel
3–5, 1
≤1
Medium
Multiple vessel
10 ppm to 5%
Vessel volume a
5–10, 3
≤1
Medium
Nonrigid chamber
10 ppm to 5%
1–1000
3, 1
1
High
Gravimetric
Low ppm to 50%
1–5000
0.1–0.002
1–150
Medium
Partial pressure
100 ppm to 50%
0.5–5000
5–10, 1
1–150
Medium
Volumetric
Low ppm to 50%
0.5–5000
3–5, 2
1–150
Medium
Partial evacuation
Low ppm to 50%
0.1–2
1–5, 1
0.001–1
Low to medium
Dynamic systems
Gas stream mixing
Single dilution
100 ppm to 50%
>5000
1–3, 1
≤1
Low
Double dilution
Low ppb to 1%
>5000
5–10, 2
≤1
Low
Injection
Syringe drive
1 ppm to 0.1%
5–1000
2–5, 1
≤1
Low
Liquid pumps
1 ppm to 5%
Very large
5, 1
1
Low
Gravity feed
100 ppm to 5%
Large
5, 3
≤1
Low
Pulse diluter
0.1 ppb to 0.1%
Very large
3–5, 1
≤1
Low to medium
Diffusion
0.1 to 500 ppm
Very large
2–6, 1
1
Low
Permeation
0.05 to 200 ppm
Large
1–3, 0.5
1
Low
Evaporation
50 ppm to 10%
Large
3–15, 2
≤1
Low
Electrolysis
Low ppm to 1%
Ltd. by soln. vol.
2–5, 1
1
Low
Chemical reaction
Low ppm to 1%
Ltd. by react vol.
3–10, 1
1
Low to medium
Static systems
Single vessel
Low
Low
Yes b
Yes
No
Multiple vessel
Low
Low
Yes b
Yes
No
Nonrigid chamber
Very low
Low
Yes
Not always
No
Gravimetric
Medium to high
Low
Yes c
Usually
Usually
Partial pressure
High
Medium
Yes c
No d
Usually
Volumetric
Medium
Medium
Yes c
No d
Usually
Partial evacuation
Medium
Low
No
Yes
Not always
Dynamic systems
Gas stream mixing
Single dilution
Low to medium
Low
No
No d
Yes
Double dilution
Medium
Low to medium
No
No d
Usually
Injection
Syringe drive
Medium to high
Medium to high
No
Yes
Usually
Liquid pumps
Medium
Low to medium
No
Yes e
No
Gravity feed
Low
Low
No
Yes e
No
Pulse diluter
High
High
No
No
Yes
Diffusion
Medium
Low to medium
No
Yes e
No
Permeation
Low to medium
Low to medium
No
Not always
Not always
Evaporation
Low to medium
Low
No
Yes e
No
Electrolysis
Medium
Medium
No
Not always
Yes
Chemical reaction
Medium
Medium
No
No
Yes
Three vessels in series.
Dilution occurs when test mixture is removed from vessel.
No, if downstream dilution is not available.
Best for gases only.
Best for liquids only.
