How does the QbD1200 control the amount of sample drawn in for each analysis and also the dilution?
Variations in the volume of the water sample analyzed and sample dilution are one of the biggest causes of sample-to-sample variance in many laboratory TOC analyzers.
The QbD1200 uses a high-accuracy syringe pump for measuring the volume of water sample analyzed and the sample dilution using the One Reagent. The syringe pump achieves a volume accuracy of +/-1% by accurate control using a stepper motor and optical encoder wheel.
A flow sensor is used to monitor the presence of the One Reagent, but the flow rate is controlled by the stepper motor and syringe. The flow sensor and syringe are both tested each time the analyzer is powered on and can be tested at any time by initiating the System Health Check through the QbD1200 menu.
If the user wants to check the accuracy of the stepper motor and syringe, then this can be achieved by turning the auto-range function off, setting the QbD1200 to take three sample analyses and placing the QbD1200 sample tube into a graduated cylinder with >50mL of low TOC water (<100ppb). The QbD1200 should extract:
(1 x 5mL forward flush) + (3 x 8mL analysis replicates) = 29mL of water