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Troubleshooting
6.12.3 Dye test to determine valve problems
Make up a series of dye standards that can be run with the method in use. Specify two
injections for each standard and use a first-order-polynomial fit.
Another option is to make up four dye standards and write a new method using exactly
the same parameters for the method in use. The concentrations for the standards could
be any sequence of four numbers in descending order. Make sure each standard is half
of the preceding one (e.g., 20, 10, 5, 2.5).
• Immerse all the reagent lines in deionized water. The manifold for this test
corresponds to the diagram of the method that is being run. Make sure that the pump
operates at 35 and the sample loop is approximately 20 cm of the Teflon 0.8 mm ID.
Place the dye standards in the standard vials and start a calibration run. Observe the
dye going through the sample loop when the valve is in the load state and then being
injected on the manifold when the valve is in the inject state. Fill the sample loop with
dye when the valve switches from the load to the inject state. If the sample loop is not
filled completely, adjust the Valve Timing.
• The calibration will pass if the standards were made properly. If poor precision is
obtained, test the valve (refer to section 6.6 on page 75) and look for clogs (refer to
section 6.5 on page 73). Poor precision could be established if the standard deviation
is greater than 10 percent.
• If the calibration passes, the hardware and manifold are in good condition. Verify the
chemistry by checking the standards and the entire method procedure again. Verify if
the manifold matches the diagram in the QuikChem method. Check the color of the
reagent pump tubes, the wavelength of the interference filter, the sample loop length,
heater temperature if it is a heated chemistry, etc.
Table 13 Example of dye standards
Standard Universal dye (mL) DI water (mL)
A100100
B50150
C25175
D 12.5 187.5
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