by Grant Lobdell
Closely related to PFAS content, fluorine analysis via combustion ion chromatography is capable of recovering PFAS missed by other analytical techniques. Regulations have already begun to be written with this analysis in mind. For example, Clean Production Action’s eco-label certification, GreenScreen CertifiedTM, defines a PFAS free foam as having < 1 ppm total organic fluorine as measured by combustion ion chromatography. In contrast, Aqueous film forming foam (AFFF) typically contains about 1% organic fluorine from fluorinated surfactants. Given that 1% = 10,000 ppm, AFFF can have as much as 10,000x the amount of organic fluorine than its fluorine free counter parts!
Many people are comfortable interpreting regulations or results displayed as a percent but less comfortable when it comes to parts per million (ppm), parts per billion (ppb), or parts per trillion (ppt). When trying to grasp how they are all related, consider percent by a different name: part per hundred (pph):
- 1 % (pph) = 1 / 100
- 1 ppm = 1 / 1,000,000
- 1 ppb = 1 / 1,000,000,000
- 1 ppt = 1 / 1,000,000,000,000
The benefit of displaying a number in one unit over another comes down to convenience. For example, consider a regulation calling for < 100 ppb of a substance. It is much easier to write and/or say 100 ppb instead of 0.00001%. It can be cumbersome to write or say such a small number.
Conversion between units can be done relatively easily. Simply divide by the number in the name of the current unit (i.e. if ppm, divide by 1,000,000) and then multiply by the number in the name of the desired unit. For example, to convert 0.01 ppm to ppb:
0.01 ppm / 1,000,000 = 0.00000001 * 1,000,000,000 = 10 ppb
Of course, the math can be simplified in the example above such that X ppm * 1000 = Y ppb. Similarly, you will find that X ppb * 1000 = Y ppt, whereas X % * 10,000 = Y ppm.
To grasp how small some of these units truly are, consider the following:
- 1 pph = 1 second out of 100 seconds OR 1 second out of 1.7 minutes
- 1 ppm = 1 second out of 1,000,000 seconds OR 1 second out of 12 days
- 1 ppb = 1 second out of 1,000,000,000 seconds OR 1 second out of 32 years
- 1 ppt = 1 second out of 1,000,000,000,000 seconds OR 1 second out of 31,710 years
When a regulation is written requesting a substance be < 70 ppt, for example, the laboratory has to do the equivalent of isolating just 70 seconds out of almost 32,000 years!
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at lab@dyneusa.com or (800) 632-2304.
©Dyne Fire Protection Labs 2020