CHLORINITY - Metrohm 785 DMP Titrino Autotitrator

Owned by jr_suhonen
Last updated: Sep 04, 2022 by jr_mechler
3 min read

Sep 4, 2022 I think any kind of com disruption resets the titration parameters, such as the com cable being unplugged and plugged back in. Happened when troubleshooting a com issue with alkalinity and cables were being unplugged, switched, plugged back in, etc. Afterwards all the chlorinity titration parameters were back at default values.

To organize previous settings from previous posts (there's a keypad that can be plugged into the titrator and is needed to change these settings):

  • Mode (the _ button)

    • Set mode to DET

  • Config

    • COM1 and COM2

      • set Handshake to none

    • Peripheral Controls

      • set Stirrer Control to on

  • Parameters

    • Titration Parameters

      • set Meas. Pt. Density to 0

      • set Signal Drift to 10

    • Stop Condition

      • set Stop EP to 1

Apr 21, 2021 Encountered the issue below with "Error 42" and found the Titrino settings had been reset and were not correct. In addition to changing the COM handshake, stop conditions, and DET mode; also had to enable the stirring control (CONFIG menu), and adjusted titration parameters(PARAM menu) of measuring point density down to 2 and signal drift down to 20 mV/min. The default value the system reset to were a measuring point density of 4 and signal drift of 50 mV/min. The change in titration parameters gives a smoother titration curve.

Eventually reduced the measuring point density to 0 and signal drift to 10 mV/min.  Speed of an IAPSO titration at this setting is about equal to the speed of an IAPSO alkalinity titration.

Oct 26, 2020 Two issues: First, when performing an analysis with the chlorinity software the Titrino display was listing an "Error 42", indicating that the COM was not correctly sending data back to the PC. The titration would start, but the graph in the chlorinity software would not update with new readings. We went into the Titrino COM port settings using the attachable keypad and changed the COM handshake to "None" so that it would not expect a reply message from the PC when the Titrino sends a data package to it. The connection parameters are accessible using the "CONFIG" keypad button. This corrected the error and the software behaves per usual. Still unsure how the handshake changed from default values, but it may have been due to tinkering in labview.

Second issue: the titration would proceed as usual, encounter the equivalence point, but instead of stopping would continue on titrating. We used the keypad to select "PARAM" > "STOP CONDITIONS" > EP, then we changed EP from 9 to 1 so that the titration would finish once the first equivalence point was determined in DET mode.

Oct 24, 2020 Silver titrode (the probe that measures chlorinity) storage info is unclear in the leaflet that comes with the electrode. This is a screen capture from the Metrohm website that confirms its storage in DI water. 

Aug 7, 2019 Replicates of IAPSO were having poor precision. The silver nitrate dispenser tip was cleaned by placing it in a sealed vial with a few mls of ammonium hydroxide (this should be done in a fume hood). Below are before and after pictures of the probe tip and frit. Additionally, the silver electrode was situated a cm or so above the stirrer bar in order for bubbles on the stirrer bar to degas, otherwise they partly envelope the electrode tip for the duration of the titration.

Jul 30, 2019 Issue with the software creating test numbers. For several samples LIMS would generate a test number of "0" when the chloride values were saved. These tests would not display in LORE. To correct this, click "View History" in the titration software, find the samples with test numbers of "0" then re-upload the results using Spreadsheet Uploader.