Workplace Monitoring
There are myriad sampling techniques for special work situations and chemicals. For example, if you draw air contaminated with an inert hydrocarbon, such a benzene, through a sampling tube with charcoal, the benzene will leave the air, and be absorbed by the charcoal, where it remains until it is desorbed in the laboratory. But how about a very water soluble contaminant such as methanol? There are many media that will absorb methanol, but they also absorb water. So in a humid environment, the water vapor will interfere with the measurement of methanol. Some gases are highly reactive and must be trapped on special media from which they can be separated later. Some chemicals degrade or change form quickly, so they must be made to react directly, so that the reaction products can be measured later. The toxicity of particles often depends on their size. We can't get into all the details, but I want you to look at these:
Direct Reading
The cheapest and most popular of the direct reading instruments is the color-metric tube. Often known by the name of their best-known manufacturer, Draeger tubes. A hand pump is used to suck a quantity of air through a glass tube. There is a chemical in the tube that changes color when exposed to the gas. The length or color intensity of the stain indicates the concentration of the contaminant. There are tubes for hundreds of chemicals available The advantage of the tubes is that they are cheap and fast. The disadvantage is that they are only accurate to plus or minus 25%. There is fine print in the instructions that indicates significant interferences for some chemicals.
Draeger makes electronic direct reading instruments too. But there are many others. For example Industrial Scientific. Look around and see the types of direct reading instruments available.