Assay Technology, Inc. manufactures several organic vapor monitors, most notably the 566, 546, and 525. Customers are asked to choose the best badge based on what they know about the environment and sampling duration. This flexibility is great for selecting the right ‘tool’ for the job, but it means laboratories have to be prepared to analyze all the different badges they will receive. It also means that labs will need sampling rates, desorption efficiencies (DEs), reporting limits, and analytical methods for each chemical on each badge. Laboratories will call us and ask what the similarities and differences are in order to determine, for example, if they have to perform DEs on both the 566 and 546 badges (no) or if they can use the 566 badge to collect 574 chemicals (yes). Below, we go through the logic. Here’s how labs can save a lot of time:
|525AT||TraceAir II, High Sampling Rate||Indoor Air Quality, STEL, and chemicals with PELs of 10 ppm or less||The 525 uses the same charcoal as the others but there is almost three times more media inside the 525 badge as the ChemDisk II badges (566, 546, 574, 549): 445 mg|
|546AT||Organic Vapor, High Capacity||Chemicals with PELs 200 ppm or greater||Exact same badge as the the 566 except 1/4 the sampling rate|
|549AT||HCFC Monitor||Specific List of HCFCs||Exact same badge as the 546 and 566 except the badge samples slower because it has only 4 holes. The badge has so few holes to reduce the amount of reverse diffusion from the very volatile HCFCs which also have high PELs.|
|566AT||Organic Vapor, Most Versatile||Most Versatile Organic Vapor, good for most applicable chemicals||The 566 uses the exact same charcoal as the 546, 549, and 574 (150 mg).|
|574AT||Halogenated Anesthetic Gases||Specific List of Anesthetic Gases||This badge is exactly the same as the 566. The difference is in the labeling and the materials are only QC’d for anesthetic gases.|
Here are some important points given the information above:
546 vs 566
- Since the wafers inside the 546 and 566 are identical, the DEs and reporting limits, ug, should be the same. The difference is in name only. So, it is necessary to perform DE or RL studies for each chemical on only one – either the 566 or 546 – and values will be the same for both products.
Varying the extraction volume to adjust the DE.
- For charcoal media, the desorption efficiency varies depending on the ratio of solvent to charcoal. For example, when we desorb the 525 for acetonitrile with 2 mL of solvent, the DE is 55.3%. When the 525 was desorbed with 4 mL of solvent, the DE rose to 74.9%. At 6 mL, the DE is 87.2%. See the table below. By using this method, even methanol is over 80%. If you want a higher DE, try increasing the desorption volume.
Using a cosolvent to increase the DE.
- For many years, Assay Technology has added a cosolvent to increase the recovery of chemicals that are difficult to desorb from charcoal. Different laboratories use different cosolvents. We use a mixture of 97% carbon disulfide / 3% benzyl alcohol. This definitely helps with many chemicals, such as alcohols, ketones, acrylates, etc. Recently, in a attempt to avoid having to use more solvent to obtain better DEs on the 525 badge (see above) we tried a 6% benzyl mixture. The recovery of some chemicals was better, but not all. If you need to increase the DE, increasing the extraction volume looks to be the best option if you are already using a cosolvent.
Match the ratio of solvent to charcoal to get the same DE for the 566, 546, and 525.
- The amount of charcoal in the 525 TraceAirII badge is 3 times the amount in the 566. If you desorb using the same amount of solvent for both badges, the ratio of solvent to charcoal will be different. So, the DEs for many chemicals will be different. But, if you extract the 566/546 badges in 2 mL and the 525 in 6 mL, the DEs will be the same because the ratio of solvent to charcoal will be the same. For example, when extracting 566s with 2 mL, the acetonitrile DE was 87.7%. When we used 2 mL of solvent on the 525, the recovery was 55.3% . It’s the same charcoal, but the ratio of solvent to charcoal is different. If you increase the amount of solvent used with the 525 so the charcoal/solvent ratio is the same as the 566 ratio (6 mL instead of 2 mL), the 525 DEs will match the 566 DEs, within a few percent. These studies were performed at levels closer to the PEL than the reporting limit.
If you have the 566 sampling rate, you have the 546 sampling rate.
- Just divide the 566 rate by 4 and you’ll have the 546 sampling rate.
566 vs 574
- If you want to use the 566 badge for 574 anesthetic gases, they will function the same. However, the 566s haven’t been verified to not contain the anesthetic gasses. So sending a field blank or two would be the most conservative approach if you do not have any 574s, but you do have 566s.
How 525 DEs Change by Extraction Volume
|566 DE||525 DE||525 DE||525 DE|
|Extraction Volume||2 mL||2 mL||4 mL||6 mL|
|Methyl Ethyl Ketone||96.0%||87.0%||97.0%||97.0%|
|Methyl Isobutyl Ketone||98.3%||92.0%||90.6%||98.4%|
|Solvent: 97% Carbon Disulfide / 3% Benzyl Alcohol|