Valve Timing Setup; Sampler Timing Setup; Air Spike Troubleshooting; Random Air Spikes - Hach QC8500 Series 2 User Manual

Troubleshooting

6.1 Valve timing setup

6.2 Sampler timing setup

6.3 Air spike troubleshooting

6.3.1 Random air spikes

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To set the method valve timing correctly is critical. Poor valve timing may result in the
absence of peaks, presence of air spikes or very small peaks. Set the cycle period
parameter as specified in the QuikChem method. When running multiple methods
simultaneously, use the longest cycle period in the QuikChem method.
Note: The "Time to Valve" value of channels 2 and higher is measured from the probe reaching the
dye, through all previous sample loops (except channel 1), to arrival at port 6 of the channel being
measured. A "Time to Valve" value must be entered for all channels.
To make sure that the valve timing is correct:
1. Inject the Universal Dye as sample.
2. Follow the sample slug and time it. Start counting the time when the sample probe
goes into the test tube.
3. When the dye reaches port 6 at the first valve, observe and note the time. This time
is called Time to Valve.
Whenever possible, leave the sampler timing at the default values.
If less sample is required for the analysis:
1. Decrease the Sample Period.
2. Test the new Run Timing setting with dye.
If either the Sample Period plus Minimum Probe in Wash Period or the Load plus
Injection Period is longer than the Method Cycle Period, the computer will return an error
message indicating the problem.
Random air spikes are more common in methods where heat is used to speed up the
chemical reaction. If the air spikes occur randomly
necessary to degas the carrier solution and the other reagents with helium. Nitrogen will
not degas reagents because the air that causes the spikes is mostly composed of
nitrogen. Argon is ineffective for degassing purposes. Read the method to verify if
reagents can be degassed.
Note: Do not degas some reagents. Check the QuikChem method to see if the reagents in use can
be degassed.
Adding a back-pressure loop to the manifold may help keep the air in solution, so that no
air bubbles are formed after the heating process.
To make a back-pressure loop:
1. Cut 200 cm of 0.5 mm ID Teflon
2. Make a loop. Use tape to keep it together.
3. Use a union fitting to connect the back-pressure loop to the flow cell exit.
(Figure 54 on page
®
tubing.
65), it may be