I seem to remember that Photoionization detectors are more sensitive than Flame Ionization Detectors. I have 2 questions:
1- is this a true statement?
2-can ethylene oxide be detected by PID/
By pgpg on Sunday, July 8, 2001 - 01:08 pm:
yes, is true, PE has a Voyager, a gc portatil PID for mesures of ethylene and oxide at ppb levels.
By Ron on Monday, July 9, 2001 - 09:11 am:
1. Some PID detectors are more sensitive than FIDs for aromatic and unsaturated compound. A blanket statement that the PID is more sensitive is not true, as the PID sensitivity is very compound dependant, and the design of the PID also affects sensitivity. The PID is measures concentration, not mass, so design is important. Lamp age and nominal eV rating also affect sensitivity.
2. Yes, but chromatography may be needed to separate the ethylene oxide from interfering compounds. A simple sniffer type device with no separation can generate false positives due to interfering compounds.
By chris knutsen on Monday, July 9, 2001 - 11:52 am:
we are using a standard ETO method with no interfering compounds. However, in the future, it appears that some regulations for medical devices will lower the acceptable levels at least 10-fold. The current methodologies would not be able to detect at these levels.
By Ron on Tuesday, July 10, 2001 - 09:23 am:
The ionization potential for ethylene oxide is 10.56 eV. The most common PID source is a 10.2 eV lamp with emission lines at 10.0 and 10.6 eV. This lamp is referred to as 10.0, 10.2, or 10.6 eV depending on the manufacturer, but they are all the same lamp. As would be expected, the ionization efficiency for ethylene oxide using one of these lamps is low. A higher energy lamp will ionize better, but will have a lower output, short lamp lifetime, and high replacement lamp cost, in addition to detecting more potentially interfering compounds. At this point you essentially have a very expensive FID that requires regular replacement of expensive consumables.
The PID is very good for some applications, but I doubt it is best for the application you need to do. There are some articles comparing detectors published a few years ago, and I don't remember any of the authors finding significant benefits from the FID. I don't have any references, but a quick search should turn up a few.
You might want to talk to Valco about the PDID detector for this application. I don't know if they have analyzed ethylene oxide, but I would expect better detection limits than a PID.
Another approach would be to collect the ethylene oxide on a sorbent tube, then use a device such as the SIS thermal desorber to inject the concentrated sample into the GC. With this approach you may be able to reach the detection limits you need with your existing FID.
By Anonymous on Tuesday, July 10, 2001 - 12:27 pm:
Excuse my butting in here, I have used the pulse discharge detector made by Valco for just this analyte and have found it to be an exceptional detector for these sorts of compounds. It is a "windowless" PID so to speak is very versatile and excellent sensitivity. It is fairly rugged and can operate at different energy levels according to the gas supplied to the detector. The same detector can also be operated in an ECD mode with very easy modifications. I apologize, I do not have their web address on hand. Hope this helps a bit,
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