Product category:
Materials Testing
News Release from: Multitrator | Subject: Photometric Cell
Edited by the Manufacturingtalk Editorial
Team on 11 September 2003
Seeing the Light; Turbidometric
Titration
Multitrator's Photometric Cell analyses Surfactants with ease, even when small amounts of sample are available.
When a cationic surfactant is titrated with an anionic surfactant (or vice versa), an insoluble ion associate is formed During the titration, this precipitate dissolves in micelles formed by the analyte
This article was originally published on Manufacturingtalk on 2 Sep 2003 at 8.00am (UK)
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At the endpoint, with no more analyte present, the ion associate precipitates, forming a turbid solution.
This will act to reduce the intensity of a beam of light shone through the titration solution.
Our software plots the turbidometric titration of an anionic surfactant (sodium dodecyl sulfate) with a cationic surfactant (cetyl pyridinium chloride).
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The photometric response is shown by the red curve.
The endpoint is not the mid point of the "S" curve, rather it is the point of maximum turbidity, as is revealed by the second derivative.
What makes the way Multitrator does photometric titrations so special? A few things - other companies use an optical probe.
This is immersed in the solution, which seems a neat idea, but it's not so good when the optical surfaces gradually acquire a layer of gunge/crud which has to be periodically removed.
It's also not such a good idea to use these probes in highly aggressive or corrosive solutions, either.
Your expensive probe may end up in several pieces, fizzing quietly on the bottom of the beaker.
Working in biological media might demand regular sterilization as well.
Further, you have to purchase another software package to handle the different way of handling endpoints.
The Multitrator photometric module overcomes all these problems.
It simply plugs into the auxiliary port on the Multitrator interface module, and derives its power from this unit.
It sits neatly in the beaker retaining ring on the burette magnetic stirrer.
Importantly, the titration solution never comes into contact with the optical components.
Our simple approach is to use a disposable glass sample vial as the titration cell.
A closely fitting magnetic turbine stirrer provides perfect, bubble-free agitation.
Two programmable LED light sources are fitted as standard.
Two matching photo-detector cells oppose each light source, which are mounted 90deg apart.
The powerful algorithm that we developed to handle the thermometric sensor signal has proven to be ideal in this application, and you don't have to buy another software package to find the endpoint.
In the application discussed here, we used a red (625 nm) LED.
The titration is remarkably sensitive.
We titrated 15 mL of a 0.0006 mol/L sodium dodecyl sulfate solution with 0.003 mol/L cetyl pyridinium chloride.
Because very little solution is used, it is ideal for biological or environmental solutions, where only small amounts of sample are available.
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