Troubleshooting A Test When Results Are In Doubt - Hach DR2400 Manual

5940022ChemAnal.fm
Apparent interferences may also be caused by a defect in the instrument or
standards. Before assuming the interference is chemical, check Branch B.
Branch H Check the operation of the instrument and/or apparatus used to
perform the test. Return to the main menu. Touch
. Touch
Wavelength Check
the instrument off then on to perform alignment and wavelength calibration if
the wavelength check is out of specification.
Check the glassware used in the procedure and make sure it is extremely clean.
Dirty pipettes and graduated cylinders can cause contamination and will not
deliver the correct volume.
If a defect is found in the instrument and/or apparatus, repeat Branch B after
repair or replacement. If the instrument and apparatus are working, proceed
with Branch I.
Branch I After determining that the procedure, reagents, instrument, and/or
apparatus are correct and working properly, the most likely cause for standard
additions not functioning correctly in deionized water is the standard used.
Obtain a new standard and repeat Branch B.
Branch J If the standard additions gives the correct result, the analyst must then
determine if one or more interfering substances are present. If interfering
substances are present, proceed to Branch C. If they are not present, the analysis
is correct.
If you cannot identify the problem, call Hach Technical Consultants at
1-800-227-4224 or visit our Web site: http://www.hach.com/forms.htm.

Troubleshooting a Test When Results are in Doubt

If the results from any Hach chemistry are in doubt, troubleshoot them as
follows:
1. Run a proof-of-accuracy check. Take a standard solution, which has a known
concentration, through the same steps as the original sample. Include
sampling and storage, digestion and colorimetric determination, if
applicable. If the results of the standard solution check are correct, skip to
step 4 below. If there is a variation in the expected results, go to step 2.
2. If the standard solutions check does not match the expected results, check the
instrument set-up and method procedure as follows:
a. Verify that the correct program number for the test being performed
is selected.
b. Verify that the units of concentration of the standard match the displayed
units. (One of the alternative forms of the analyte may be in the display.)
For example: Molybdenum may be shown as Mo instead of MoO
c. Verify that the sample cells called for in the procedure are the ones
being used.
d. Verify that the reagents are correct for the sample size being analyzed.
e. Verify that the reagent blank value stored is for the current procedure. It
may be from a previous lot of reagents and therefore not representative
of the current reagent lot.
. The wavelength should read 404.66 ± 1 nm. Turn
Read
Chemical Analysis
then
System Checks
4
Chemical Analysis
Page 37
.