Dear Researchers
Kindly comment on the problem I am facing during titration.
To quantify chlorides ion in concrete, I prepared the sample following ASTM C1152. The chlorides were extracted from 10g concrete powder and the concrete I am testing is composed of OPC or FA/GGBS blends (FA/GGBS blended concrete is a geopolymer concrete with various alkali concentrations).
Now the problem is, when analyzing concrete samples, EP point was not detected but when analyzing blank sample (without concrete and with 2 ml NaCl) the EP point was detected at around 1.98 - 2 ml AgNO3 volume. I repeated the test atleast 10 times both on concrete and blank samples, each time the result is same.
What could be the possible problem? I am following the steps mentioned in the standard. since the blank titration was accurate, I assume there is no problem with titrode or machine.
One more thing I want to mention is, I successfully found EP for sample extracted from FA/GGBS geopolymer concrete activated by low Na2SiO3/NaOH ratio activator, where NaOH concentration was 8M.
Additional information: I am using Metrohm titrator and titrode is Ag with AgCl coating. Sulfides were not removed by oxidation (yet I was able to find EP for geopolymer concrete activated by low Na2SiO3/NaOH ratio activator, where NaOH concentration was 8M)
Kindly share your opinion so that I can rectify the methods I am following.
Thankyou in advance
#chloridetitrationn
There are a number of reasons why acid-soluble chloride extracted from concrete cannot be titrated to the EP (End Point) using potentiometric indication. Here are a few typical explanations:
Low Conductivity: When utilizing a potentiometric approach to detect the endpoint, it can be difficult if the solution being titrated has very low conductivity. Potentiometric titrations are dependent on voltage or potential changes, which in low-conductivity solutions may be negligible.
Insufficient Mixing: A good titration depends on the concrete sample being properly mixed with the titrant and indicator. It can be challenging to precisely identify the endpoint when there are regional fluctuations in chloride concentration due to inadequate mixing.
Additional Ion Interference: The detection of the endpoint may be challenging if additional ions that may interfere with the potentiometric measurement are present in the concrete or the titration mixture (such as ions that conduct redox reactions).
Inadequate Indicator: In a potentiometric titration, the indicator selection is crucial. Having trouble monitoring the endpoint can result from using an unsuitable indicator or not adding enough of it.
Electrode Issues: Difficulties in identifying the endpoint might also be brought on by issues with the reference electrode or the indication electrode. Make that the electrodes are calibrated and in good condition.
Titration Rate: The endpoint can be more or less detectable depending on how quickly the titrant is introduced. At the endpoint, it could be difficult to detect minute potential changes if the titrant is introduced too quickly.
Sample contamination: Organic matter or other impurities in the concrete sample can interfere with the titration and make it difficult to identify the endpoint.
Inaccurate Titrant Concentration: Make sure the titrant's concentration is precisely known and prepared. An improper endpoint determination can result from an inaccuracy in titrant concentration.
Titration Method: The method of titration, such as manual or automated titration, can have an impact on the precision with which the endpoint is detected. Systems for automated titration might provide more accuracy and control.
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