Chromatography Forum

I work with a HPLC Varian PROSTAR 230 and a column RP C18 with precolumn.
Working with 100% methanol (flow 1 ml/min) I have 160 bar!!!! I tried to clean the column with different solvents and I changed the precolumn but I had any good result....today I started a run without the column using the union, but I still have 145 bar with 100% of methanol.
100% avetnitrile allow me to work with 40 bar.
when I try to change from acetonitrile to water I get 220 bar when the mixture is still 23% water and 77% acetonitrile....Please can nayone help me in solving this problem?
Today I will try to clean the system using the union and not the column....with a low flux (0.4 ml/min) and changing solvents with different polarity....hope to tell new some good news!

This sounds as if there's something stuck in the HPLC causing the high backpressure. The different pressures when using different solvents for flushing are perfectly OK due to the different viscosities - pure acetonitrile will give you the lowest pressure, methanol/water the highest and pure methanol will be somewhere in between.
If you have some knowledge of the HPLCs plumbing, you can loosen certain fittings in order to isolate the part where that obstruction sits. If it's a capillary, you can try to backflush it.
Concerning flushing of the system, hot water is always a good idea . In any case, remove the column for trying to flush out that obstacle...

Hi If you have varian 210/218/SD-1 pumps, check the filter inside of the Mixer (small cylinder) - it seems that this filter is blocked.

best regards
Chris