How is valve timing optimized on the Lachat QC8500 FIA?

Document ID

Document ID TE5438

Published Date

Published Date 25/01/2018
Question
How is valve timing optimized on the Lachat QC8500 FIA?
Summary
Setting time to valve for Lachat FIA
Answer
Valve timing parameters should be entered into Omnion software following the Lachat Quikchem method to ensure the best results. The Time to Valve parameter must be measured and then entered into the Omnion software. If valve timing is not correct, it is possible to inject a poor slug of sample, air or wash bath water.
Valve timing is not just to fill the sample loop with sample. Correct valve timing will guarantee that the loop is rinsed with some volume of sample before actually injecting. If the sample only fills the loop and immediately injects there can be some carrier mixed with the sample and a pure slug of sample will not be injected. This can cause less color development and more variability between injections of the same sample/standard.
  • Valve timing parameters - Most of the valve timing parameters are provided in the Lachat method. The exception to this is Time to Valve. Time to Valve will vary from system to system depending on lengths of tubing used between sampler and system as well as whether or not the system includes a dilutor. The user will set the Time to Valve by running dye as a sample and timing how long it takes to reach the valve.
  • Time to valve - To set this timing run some dye as a sample. A stop watch or second hand will need to be referenced. Start time begins when the probe drops into the sample. Stop time is when the dye reaches port six of the valve being timed. The time that transpires from start to stop is Time to Valve. After the value is determined it can be entered in the Timing tab of the Run Properties Window. Select the valve being timed on the right hand side of the Timing tab and enter the value in the Time to Valve field.  Once it is entered into the software it can be verified by running the dye again. If it was set correctly, once can hear the valve first turn when the dye reaches the valve (within a second or so).
Some additional topics to be aware of when working with Time to Valve
  • Sample line pump tube - It is helpful to trim the sample line pump tube. As the sample must travel through this pump tube to reach the valve its length affects the Time to Valve. Though pump tubes have specifications for inner diameter they do not have a specification for length and this can vary from lot to lot. We recommend users trim each pump tube used for the sample line so that there is one inch outside of each tab. If the sample line pump tubes are each trimmed to the same length each time there should not be a significant change in Time to Valve when this pump tube is changed.
  • Flow concerns - If time to valve is measured multiple times and it is not consistent, it indicates the sample line has a flow issue of some sort. This could be an old pump tube, a valve in need of service, dirty waste line, clog/crimp in tubing etc. The valve injects the dye onto the manifold when it turns a second time. If the dye does not get injected or struggles to do so there is an issue with the flow of the carrier line. The procedure above should be followed for most one channel methods. An exception to this would be inline digestion/distillation methods and any method which uses a dialysis block prior to the injection valve. 

How is valve timing optimized on the Lachat QC8500 FIA when running more than on channel at a time?