Manual End Point Determination (Mepd); Automatic End Point Determination (Aepd); Auto Detection; Parameters Used In The Calculation Of The Analyte Concentration - Hach AutoCAT 9000 Instruction Manual

5.2.2.1 Manual End Point Determination (MEPD)

5.2.2.2 Automatic End Point Determination (AEPD)

5.2.2.3 Auto Detection

5.2.3 Parameters Used in the Calculation of the Analyte Concentration

5.2.3.1 Titrant Concentration

5.2.3.2 Sample Volume

50081_AutomatedTitration.fm
MEPD requires the user to manually position the cursors on the instrument display to
define separate linear regions of the titration curve on each side of the end point (i.e., the
break in the titration curve). When selecting line segments, it is generally advisable to
select points closer to the end point of the titration, and to avoid, as much as possible,
"noisy" sections of the curve. Select a pair of lines that intersect as near as possible to the
break in the titration curve. After the linear regions have been selected, the linear least
squares regression lines are fit through all the points between each pair of cursors. The
intersection of the two regression lines determines the end point. More guidelines for
Manual End Point Determination can be found on page 135.
AEPD allows the AutoCAT 9000 to search for a pair of intersecting lines that best fit the
titration curve. The end point is determined from the intersection of the two best-fit lines.
Normally, when a user runs an analysis on the AutoCAT 9000, the instrument will go
directly from data collection to the zoom window. The instrument will stop in the zoom
window, allowing the user to select the desired range of data points and the mode (AEPD
or MEPD) to be used for end point determination.
If the auto-detection feature is enabled (set to Yes), then the instrument will proceed
directly from data collection to AEPD without the usual intervening zoom window.
Following AEPD, the results are displayed and the user can accept the results or
reprocess the data using either AEPD or MEPD.
After the end point has been determined, the AutoCAT 9000 automatically calculates the
corresponding analyte concentration. The titrant concentration, sample volume, and
dilution factors are used to calculate the analyte concentration, regardless of the method.
In addition, the back titration method uses the concentration and volume of the reductant
solution used to fix the sample. Each parameter must be properly set prior to running
an analysis.
A Number of Decimals parameter is available in supervisor-level mode to set the number
of decimal places used to report the analysis. For example, if Number of decimals is set
to "4", the experimental results will be reported as 0.3296 mg/L. If it is set to "2", the
result would be displayed as 0.33 mg/L.
The titrant concentration (mN) can be entered manually or determined experimentally
using the appropriate embedded titrant calibration routine. The exact concentration of the
titrant is needed when entering the titrant concentration. See Obtaining the Certificate of
Analysis for Hach Reagents on page 41.
The sample volume (mL) is the volume of the sample solution actually placed on the
instrument. This is a run-time parameter, allowing it to be changed each time a sample
analysis is performed. The default sample volume is 200 mL. If the sample volume is
changed, the new value is used as a default until the method defaults are reset or the
value changed again.
Collecting and Accessing Data
Collecting and Accessing Data
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