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2. ©2009 Mourne Training Services Dear Lab Tech Guy, Sometimes while using Agilent HPLC, I am facing problems of more back pressure while purging. Someone told me that it is due to the frit. What is the exact function of this frit and how can I increase the life of the frit? Also, is this frit present in Waters HPLC as well? Yours, Sanjeev (Haryana, India)

3. Dear Sanjeev, The frit you refer to is located in the purge valve on an Agilent HPLC system. Its purpose is to protect the HPLC system and the column by removing particulates from the mobile phase. This PTFE frit (shown on the right) is intended as a disposable part which is changed on a regular basis, hence the low cost at approximately $30 for a pack of 5. The frit should be changed when you experience high back pressure during purging, the Agilent recommendation is as follows: “The most common way to determine if the Purge Valve frit needs to be replaced is by opening the Purge Valve and establishing a flow of 1 mL/min of Methanol. If the pressure is more than 7 bar, the frit should be replaced”. Exchanging the frit is simple (there is a useful demonstration video on the Agilent website). Make sure to inspect the gold seal when you are changing the frit and replace it too if there is any sign of damage. ©2009 Mourne Training Services Expanded view of the purge valve PTFE frit Gold seal

4. ©2009 Mourne Training Services When you remove an old frit, inspect it carefully. Does it shown any signs of discolouration? Black stains are indicative of microbial growth and this may be one reason why your frits need to be changed very often. To maximise the lifetime of the purge valve frit you need to pay particular attention to your mobile phase. Make sure that your mobile phase is very clean and if possible filtered. Mobile phase reservoirs which contain water or solutions of buffers are susceptible to growth of microorganisms and this is the main source of the discoloration on the purge valve frit. Be very careful when applying expiry dates to these types of solutions, it is preferable to prepare these freshly each time they are required.

5. The Waters Alliance HPLC systems do not have a frit in the purge valve. However, there is an in-line filter which is located between the pump and the injector (shown on the left). The purpose of this component is also to capture particulate contamination. When the filter becomes blocked (pressure increase will be observed), it may be removed from the casing and replaced, or it is also possible to extend its life by cleaning in methanol using sonication. In summary then, filtering the previous for the main advice, the frit is there to help protect your HPLC system and changing it is a normal maintenance procedure. Make sure your mobile phase is as clean as possible (no particulates, no microbial growth) to extend the lifetime of your frits. Yours preventatively, ©2009 Mourne Training Services

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