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- Posts: 148
- Joined: Wed Jul 03, 2013 1:51 am
- Location: Michigan, USA
I have an interesting task on hand. It will be solvable one way or another - I am not terribly worried. But I am thinking about elegant and simple approaches to sample prep for transfer to a production lab. This procedure should be fool-proof.
We have acidic analytes with very limited water solubility at low pH but excellent solubility at high pH. Samples will come in at pH 10-14, so up to 1M excess NaOH. I need to adjust pH before injection, especially since there will be a high throughput of samples. But, I do not want to lower pH so much that the analytes or ISTD might precipitate.
I like this approach because there is no danger of dropping the pH so much that the analyte will precipitate but at the same time the pH won’t be terribly high anymore.
I am thinking about this in case we use the internal standard approach:
Take 1g of sample solution and note weight.
Add 10 mL DI water
Add 1 mL of saturated sodium bicarbonate solution (1.2M at RT).
Add 2.00 mL of ISTD solution by dispensette (or weigh in)
1 uL will be injected into a column flow of 1 or 1.5 mL/Min of phosphate buffer at pH 2.1.
The mobile phase will be acidic and this is my worry with this approach. Will the bicarbonate in the injected sample cause trouble due to its transformation to H2CO3 / CO2? The pressure in the HPLC should keep it from bubbling out and so should the backpressure regulator at the UV detector.
An alternative approach would be to use a phosphate buffer around neutral pH.
Any thoughts?