sample flush-out factor of Agilent HP1100?

[jduan]

Dear experts out there, I have one question about the sample flush out factor of Agilent HP 1100.

In the definition, it says that the sample flush-out factor ensures that the sample is thoroughly flushed out of the syringe, past the capillary seat and valve.

The volume is calculated as:

factor x (injection volume + seat capillary + valve volume)

However, as the system is designed, during an analysis, the injection valve is in the mainpass position. The mobile phase flows through the well-plate sampler metering device, sample loop, and needle, ensuring all parts in contact with sample are flushed.

So will the mobile phase flow through the syringe, seat capillary and valve? I think syringe should be flushed by mobile phase during analysis. Some part of the valve may not be washed by the mobile phase during analysis because valve switched from loading to injection.

So which part is really the part that is not flushed by the mobile phase during analysis and needs to be washed by "flush-out factor"?

And when did the flush-out happen? Before the run, or after the run or during the run, it is flushing some part of the system at the same time?


Thanks so much!!!

jin

[Mark Tracy]

Under normal operating conditions, you are right. However, there are circumstances where you have the valve in bypass during the analysis. For example, doing very fast gradients at low flow, you may set the valve to bypass so as to eliminate the delay volume, but you need to wait for the sample to be fully flushed after injection before switching the valve. Similarly before the next injection, you need to wait to be sure that the initial mobile phase has filled the loop. You also need to use the flushout factor if you are doing automated sample prep with your autosampler. (In case you are wondering, I have made all those mistakes, and it took me a whole day to figure out what was wrong.)

The Agilent 1100 is a very popular example of the split-loop injector design, but not the only one.