Dilution; Reductant Concentration; Reductant Volume; Analysis Calculations - Hach AutoCAT 9000 Instruction Manual

Collecting and Accessing Data

5.2.3.3 Dilution

5.2.3.4 Reductant Concentration

5.2.3.5 Reductant Volume

5.2.4 Analysis Calculations

Collecting and Accessing Data
Page 46
If a sample solution is diluted prior to analysis, the sample parameter Dilution should be
enabled (set to Yes), allowing access to three other parameters (Predilution vol., Final
dilution vol., and Sample vol.). These parameters allow the calculated analyte
concentration to be corrected for dilution and are only applicable when dilution is
enabled.
This is generally done to bring the analyte concentration into the proper range for
analysis. The AutoCAT 9000 can automatically correct any measured analyte
concentration for sample dilution and three parameters are used to calculate analyte
concentration:
•
Predilution volume is the volume of the original sample
•
Final dilution vol. is the volume of the sample after dilution
•
Volume for Test is the volume of solution taken from the diluted sample
and analyzed.
Normally, AutoCAT returns the concentration of the sample actually presented to it (i.e.,
the concentration of the sample placed in the analysis beaker and analyzed by the
instrument). Using the dilution information, the AutoCAT can automatically convert the
concentration measured for the diluted sample into the concentration of the undiluted
sample.
When performing a back titration the sample is fixed by spiking it with reductant (either
PAO or sodium thiosulfate) solution. Reductant concentration is the concentration (mN)
of the solution used to fix the sample. The exact concentration of a Hach reductant
solution can be obtained. See Obtaining the Certificate of Analysis for Hach Reagents on
page 41.
In a back titration the sample is fixed by spiking it with reductant (either PAO or sodium
thiosulfate) solution. Reductant Volume is the volume (mL) of the reductant solution
used to fix the sample.
When two or more consecutive new tests (as opposed to new samples) are run, the
AutoCAT 9000 automatically calculates the mean and the standard deviation of the mean
for the results obtained from the individual tests. This is equivalent to making several
replicate measurements starting with identical samples for each measurement. The
standard deviation of the mean is different than the standard deviation of the replicate
measurements.
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