Troubleshooting - Hach Micro Dist Manuel D'utilisation

Figure 6 Replace the fuse

Troubleshooting

Problem
Low or not consistent
analyte recoveries
Large blanks in
cyanide
Sample boils too
intensely in the sample
tube
22 English
Possible cause
Tubes are not pushed
fully into the heater block
Too much NaOH was
added to the samples
Sample tubes were not
removed immediately
after distillation
Too much liquid was put
in the sample tube which
caused distilled sample to
be pulled back into the
sample tube
A method expects a
higher NaOH
concentration so the
samples give high
recoveries
A method expects a lower
NaOH concentration so
the samples give low
recoveries
Contaminated MgCl
2
—
Push tubes into the heater block until the stop ring on the
sample tube hits the heater block.
Lower the pH with sulfuric acid before distillation.
Note: If too much NaOH is added to samples, the amount of HCN in
the samples is decreased.
Immediately remove the sample tubes from the tube
assembly after distillation.
Use a calibrated pipette to dispense sample, releasing
agent, neutralizing agent and/or buffer solution into the
sample tube.
For method Cyanide–1, the method of determination which
follows the distillation must anticipate both 6.0 mL samples
and 0.25 M NaOH. For example, when using USEPA
Method 335.2 and scaling down the reagent quantities, but
the solution is diluted to 100 mL, color development will not
occur. See the scaled-down version of this method for an
example.
Some "auto-analyzer" methods expect a different
concentration of NaOH. If the undistilled standards used in
these methods are not made up in 0.25 M NaOH, then
there will be a matrix effect when the Micro Distilled
samples, which are always in 0.25 M NaOH, are
determined.
Use only 99.9999% pure or other ultra-pure grade. Use high
quality grade (e.g., HPLC) of sulfuric acid when possible.
Add one Hengar granule or other small (ca. 1 mm diameter)
boiling stone to the sample tube.
Solution