Chromatography Forum

Dear All,
I was was wondering if anyone has any reliable methods for determining the time delay from the detector to the collection point. I have tried various methods such as introducing air bubbles but I am not happy with the reproducibility. I have heard a dye can be introduced. What dye can be used which is compatible with a RP column and what wavelenght should I monitor at?
Cheers,
Sat

Instead of using the HPLC pump, use a precision air-tight syringe. Disconnect the capillary from the detector outlet, as near the flow cell as possible. Flush out the line with air. Attach the syringe and measure the volume to fill the line. If you need a dye to help visualize, red food coloring works well. Also, a small leader of tranparent teflon tubing between the syringe and the capillary might make the measurement easier.

This is similar to how I used to QA precision tubing for post-column reactors.

I'm not sure as to what exists between the detector and your collection point. If it is just a piece of tubing and it is detachable, then you can weigh it when full of pure water pumped from the HPLC. You will have to devise some way of capping it to prevent the water coming out. Then fill it with something volatile (methanol?) and blow air through it to dry it thoroughly. Weigh it again (with the dry caps on again). The difference in weight is the volume of the tube. Remember that weighing can be very accurate.... When you have the volume you can calculate the delay time considering the pump flow rate.

This method worked for me but might not work for you, depending on exactly what there is in your system between the detector and collection point.....