Way back in 2007, I wrote a piece on a simple chemical reaction which is now proving to be highly useful in chemical analysis for process and quality control. To save you having to scroll down to the bottom of the blog, here it is again:
You can use this reaction to determine by thermometric endpoint titration (TET) sodium, aluminium and fluoride (but not potassium), because the reaction is exothermic. I'm going to stick my neck out here, and say that this reaction offers the first viable titration method for analyzing sodium. Sure, there's been others, but none have proven to be successful. A titration based on the insolubility of zinc uranyl acetate has been around since 1931, and a complexometric procedure was reported in 1970, but my argument is that if they were of any real practical use, you would in fact see them being used. You don't. And yet titration is a great technique for routine process and quality control. Automated titration instruments don't take up much bench space, infrastructure is minimal, and lower-skilled operators can be used, providing they are well trained and well supervised.
In the case of TET, frequently it is unnecessary to filter sample solutions prior to titration. Further, the sensor is really just a fast-responding electronic thermometer. The probe doesn't need calibrating and requires little maintenance, the titrations take place in regular vessels (no insulation required), you don't need a reference electrode, the probe is always 24/7 ready - what could be easier?
"But wait a minute", I hear you say, "we're already titrating for sodium in food - we use silver nitrate as the titrant. That's all we need to do, isn't it?"
Well, no. It isn't good enough any more. The silver nitrate titration assumes that all sodium present is in the form of sodium chloride, common salt. You actually titrate chloride (and other halides) with the silver nitrate, and assume that all chloride is present as sodium chloride. The trouble is, that not all sodium in food comes from added sodium chloride. Lots of other sodium salts are added to processed foods; some are preservatives, some are flavour enhancers, and then there's emulsifiers and also stabilizers; all sorts of different sodium salts are used in foods. There's something else to consider: some manufacturers are seeking to reduce the sodium content of the food, while minimizing the impact of the "saltiness" of the food. They're doing this by substituting potassium chloride for some of the sodium chloride that's normally added. Look at this label from a container of margarine:
Potassium chloride is also being used as a sodium chloride replacement in snack foods as well. Check for the food code E508 on the label, if potassium chloride isn't mentioned by name.
The titration itself is quite straightforward. However, as in every analysis involving food, you have to pay attention to the sample preparation. The main aims are to liberate all the sodium from the food matrix, and to obtain a solution that is suitable for titration - not too viscous, and no lumps. Fortunately, you don't have to worry about turbidity or fine particulates, because there's no sensitive sensor membrane to foul or reference junction to clog. Even fatty foods can be handled with the appropriate sample preparattion. When you're considering the determination of sodium by TET in a food for the first time, there is a need to think carefully about the sample preparation options you need to consider.
Recently, I wrote a paper which gives some examples of the determination of sodium in various foods. You can download a PDF copy of the paper "Novel method for determination of sodium in foods by thermometric endpoint titrimetry (TET)" by clicking on the link. It was published in the January 2014 edition (Volume 3, Number 1B) of the open-access Journal of Agricultural Chemistry and Environment. If you don't have much time, there's a condensed version as a presentation-style PDF which can be downloaded from here.
In the case of TET, frequently it is unnecessary to filter sample solutions prior to titration. Further, the sensor is really just a fast-responding electronic thermometer. The probe doesn't need calibrating and requires little maintenance, the titrations take place in regular vessels (no insulation required), you don't need a reference electrode, the probe is always 24/7 ready - what could be easier?
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| Thermoprobe thermometric titration sensor |
Potassium chloride is also being used as a sodium chloride replacement in snack foods as well. Check for the food code E508 on the label, if potassium chloride isn't mentioned by name.
The titration itself is quite straightforward. However, as in every analysis involving food, you have to pay attention to the sample preparation. The main aims are to liberate all the sodium from the food matrix, and to obtain a solution that is suitable for titration - not too viscous, and no lumps. Fortunately, you don't have to worry about turbidity or fine particulates, because there's no sensitive sensor membrane to foul or reference junction to clog. Even fatty foods can be handled with the appropriate sample preparattion. When you're considering the determination of sodium by TET in a food for the first time, there is a need to think carefully about the sample preparation options you need to consider.
Recently, I wrote a paper which gives some examples of the determination of sodium in various foods. You can download a PDF copy of the paper "Novel method for determination of sodium in foods by thermometric endpoint titrimetry (TET)" by clicking on the link. It was published in the January 2014 edition (Volume 3, Number 1B) of the open-access Journal of Agricultural Chemistry and Environment. If you don't have much time, there's a condensed version as a presentation-style PDF which can be downloaded from here.
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