Issues with using low/lower purity analytical ref standards

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

8 posts Page 1 of 1
Hi all,

Just a quick question. Would anybody envision there being an issue with using say a 50% standard reference solution in HPLC? (for quantitation, assays etc. using UV/(PDA) detectors)

Obviously it's best practice to use a high purity, well characterized, in-date primary ref standard with a CofA from a reputable company etc., but is there actually a good reason why a 50% certified solution of the same material (complete with CofA, in-date etc.) can't be used?

The rationale is that the 50% is much cheaper, obviously the dilutions for the working standard solutions will be adjusted such that the calibration curve/range match.

**Note: I would first plan of validating the 50% purity by comparison with the pure, >98% or so ref standard.

Thanks
In general, we used the highest purity reference materials we could obtain.

My only concern would be whether that purchased standard solution would be used just once, or "stored" for future uses.
In simple terms the use of a 50% pure "Std" means that 50% of the material may not be known and... more importantly, not known how it may interact with actual samples. This alone would usually invalid any such method.
I've worked in multiple places that have done this. Typically it was easier to have a certified solution of some standard, usually a salt or metal, that was diluted for the calibration curve or as a check standard. Just make sure the "50% standard" is reputable and that the stabilizers that may or may not be used wont cause an unwanted matrix effect.
We used pre-made standards for the actives for our pest control products, because the pure standards were significantly more hazardous to handle.

We did have an issue with one at first because the light produced from sealing the glass ampule degraded some of the active; we worked with the supplier to eliminate this for the future.
I've had enough problems with claimed purity of 'reference' standards to not even consider using a sample reported to be 50% pure. YMMV.
I think the main question is: Is it 50% pure or is it a solution that is 50% w/w or v/v or w/v?

If it is the solution, and the solvent won't interfere with the analysis then that is the same as a certified standard solution. If it is something like 50% Potassium Chloride in various other salts then probably not a good idea.
The past is there to guide us into the future, not to dwell in.
depends on the method and the situation, and you're going to have to do the necessary validation. To take two extreme examples: (1) if it's a natural product with known UV absorbance at 300nm, the natural source is known to contain 5 closely related compounds, and the 50% purity is based on the supplier's HPLC trace at 300nm showing the presence of the 4 other compounds as natural impurities, separate from the main peak, then provided your assay is specific to the correct compound, and unaffected by the other 4, I wouldn't have a problem in believing your results. This is quite a common situation if you're working on very weird natural products. But if (2) some joker has, with perfectly pedantic correctness, decided to sell D-expensivestuff and L-expensivestuff as 50% purity standards, when actually they synthesized a racemic mixture and didn't bother to separate the two stereoisomers, then your C18-column-based method is going to be seriously messed up...
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