Hach AutoCAT 9000, Instruction Manual

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Collecting and Accessing Data
50081_AutomatedTitration.fm
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Section 5 Collecting and Accessing Data
5.1 Using the AutoCAT 9000 for Amperometric Methods
The following analysis procedures, based on Standard Methods, are embedded directly
in the instrument software:
• Forward titration for free chlorine
• Forward titration for total chlorine
• Back titration for total chlorine
• Forward titration for chlorine dioxide
Hach sells pre-standardized titrants, prepared according to Standard Methods, for both
forward and back titrations. The 0.00564 N phenylarsine oxide titrant (Cat. No. 1999-53)
has a shelf life of >1 year in the unopened bottle. The unopened 0.0282 N Iodine
Standard Solution titrant (Cat. No. 23333-53) is stable for 6 to 12 months.
Periodically recalibrate the titrants after opening to ensure accuracy. Dispense reagents
directly from the product bottle to eliminate contamination from transferring them to
separate containers.
5.2 AutoCAT Titration
AutoCAT 9000 functions can be separated into three categories: (1) data collection,
(2) end point determination, and (3) calculation. Each category is described in the
sections below.
5.2.1 Data Collection
The AutoCAT displays the titration curve (current (µA) vs. titrant volume (mL))
graphically in real time, as it dispenses titrant and measures the current. After the
titration is complete, the user can choose between a fully automated or manual routine to
determine the end point. Following end point determination, the AutoCAT 9000
automatically calculates the analyte concentration.
The titration curve is constructed by plotting the measured current as a function of the
volume of titrant added. Several parameters, which must be set prior to data collection,
are available to control the data collection process. These parameters include the
(1) current range, (2) volume increment, (3) predose volume, and (4) Auto-scaling.
5.2.1.1 Current Range
Current Range allows the user to set the maximum current (in µA) expected for a
particular titration. The AutoCAT 9000 allows four possible settings (2 µA, 20 µA,
200 µA, and 1 mA) for the current range. The default setting (20 µA) setting is adequate
for most purposes. The 2 µA setting is recommended when analyzing samples with
concentration less than 0.600 mg/L Total Chlorine.
Note: The 200-µA and 1-mA settings are available for experimental use, and are not
recommended for most titrations.