9 Reasons why an XSD is a better bet than an ECD
Posted on November 7th, 2012
If you own and use electron capture detectors, you will be well aware that despite some useful attributes, they suffer some serious disadvantages.
The electron capture detector contains a weak radioactive source that, in practical terms, offers no risk to anyone or the environment, but is, nevertheless, subject to regulations that have a habit of changing at random intervals and often catch people out in the process.
The ECD is unique among GC detectors, in that it brings with it significant paperwork and administrative issues.
In the chromatography lab, the ECD can be incredibly sensitive for many halogen containing compounds, but, rather annoyingly, has a very low (or no) response to some others.
The ECD is a fussy beast too. Unless it is in constant use, the detector will take many hours (or sometimes days) to stabilize. It has a weak response to oxygen, but there is a lot of oxygen around in the air and that means that you have to maintain ECD systems in a highly leak tight condition and also pay careful attention to the purity of the carrier gas you are using. An oxygen trap is essential. Keeping the detector clean and oxygen free is vital to reduce chemical noise if you are using the ECD for trace analysis.
Experienced users of ECDs will often keep a separately labeled stock of syringes for ECD use. This is to avoid the possibility of using a syringe that has been used previously with chlorinated solvents. Make the mistake of using the wrong syringe and you will send your ECD response off the top of scale, where it will stay for a very long time – you may well end up having to replace the detector with a new one.
The good news is that there is an alternative to the ECD that is altogether easier to live with – the Halogen Selective Detector (XSD) from OI Analytical.
Comparing the XSD with the Electron Capture Detector.
It is useful to compare the two detectors, because for many applications that currently call for the ECD, the XSD is a better alternative:
- The XSD has no radioactive source and requires no license, no special administration procedures and no wipe testing – unlike the ECD.
- There are no special regulations concerning ownership, maintenance, transportation or disposal of an XSD – unlike the ECD.
- The XSD is insensitive to oxygen and water – unlike the ECD.
- The XSD has a wider linear range than the ECD.
- The XSD’s response to chlorine is not compound specific – unlike the ECD.
- The XSD has a much shorter stabilization time – 30 minutes compared with a day or so for the ECD.
- The XSD has better selectivity towards halogen compounds compared with the ECD, so samples typically will need a less rigorous clean-up.
- The XSD is simple to use and easy to maintain; it is much more suitable for use by inexperienced operators than the ECD.
- The XSD is self-contained and may be installed on just about any make or model of GC.
The one remaining issue to address is that of sensitivity. This will vary of course, from compound to compound, but if we take Lindane as an example, 8.2 pg Cl on column will give a 16:1 signal to noise ratio and a detectivity of <1pg Cl/sec. For Lindane this gives a sensitivity of 1 pg/sec.
In round figures, this means that the XSD is 10-20 times less sensitive than an ECD, however, in the real World, what really matters is signal to noise when working with sample extracts (rather than standards) and it is here that the XSD can have a decisive advantage due to its much better selectivity.
In practical terms, for most applications, the XSD represents a perfectly feasible (and very attractive) alternative to the ECD.
A great example of this can be seen in this application note, that compares the results obtained from spiked garlic extracts. Garlic extracts contain a lot of sulphur compounds which give a huge background signal with an ECD (even after a florasil clean-up). With the XSD, running the same extract, the sulphur background is dramatically lower, due to the XSD’s greater selectivity.
If this sounds like something you ought to investigate, please get in touch. We have an XSD in our Cambridge laboratory and would be happy to show you what it can do for you.
Please call us now on +44 (0) 1223 279210, or email email@example.com.