Analysis of acid mixtures in explosives is far from straightforward with conventional titration, but some cleverness reduces the complexity enormously
If you are in the business of nitrating organic compounds (for instance, the manufacture of most conventional explosives), you will be faced with the problem of the analysis of the acid mixtures used in those processes.
They mainly comprise mixtures of sulphuric and nitric acids, and the conventional method of analysis is long, corrosive, and decidedly environmentally unfriendly.
Unfortunately, you can't differentiate the sulphuric from the nitric in a conventional acid-base titration. You only get one endpoint, no matter what technique you use. Here's how it has been done in many labs, probably over the past century or so: you take two aliquots of the acid mixture.
On one aliquot you determine the total acid content.
On the other aliquot, you slowly boil off the nitric acid component until you're left with the sulphuric acid.
You then titrate the residual sulphuric acid, and then with a little mathematics calculate the nitric acid content.
Just think of all those lovely corrosive nitric acid fumes being swept up through the fume hood and into the environment.
It must gladden the hearts of fume hood sales people.
The people at Stirling say that Multitrator has a better way, using two of its great features: the thermometric probe, which can be used for many different types of titration; and the ability to 'chain' methods using different titrants to make a single titration sequence which can determine two or more analytes.
Since we can't resolve the nitric and sulphuric acids with a single acid-base titration, we have to think laterally.
We use two contiguous titrations.
The first involves the titration of the sulphuric acid as sulphate, not acid, using barium chloride as titrant.
The second titration follows on immediately after, titrating the total acid content with standard sodium hydroxide solution.
Both titration results report to the same line on the same spreadsheet, and with a bit of Excel magic we calculate the individual sulphuric and nitric components.
Importantly, it is very much faster than the existing method, permitting much better process control.
