Does standard addition work in my analysis?

[Simon001]

my post has been modified as below.

Thanks

[Simon001]

Hi all,

I am working on an LC-DAD analysis of a chemical that presents in my sample (solid) background with high concentration (~1%). As no proper blanks are available, I am planning to make the calibration curve using standard addition approach.

But the problem is that the commercially available standard is in solution and its concentration is 0.1% much lower than the background level. My plan is:

1. Dissolve my sample (for example, dissolve 0.1 g of my sample into 40 mL solvent);
2. Take 1 mL of the solution (3 or 4 replicate samples) then dilute it to 10 mL;
3. Perform standard addition by spiking the standard into the diluted samples in step 2;
4. Conduct LC analysis.

As my standard is added after the sample dilution, I do not know if it works for the quantitative analysis. Is there any paper I can refer to?

Thanks

[lmh]

I'm not sure you need a paper. If you split the job into two separate parts and imagine two separate people doing it:
Person 1 takes a sample, dissolves and dilutes it. They give it to...
...You, Person 2, who analyses it using the well-known approach of standard addition. You don't need to worry about the sample before it reached you, just that you have your method validated and functional for a sample in the correct matrix, at the correct expected range of concentrations etc.; frequently an analyst won't actually know the details of how the sample was taken.
Provided Person 1 has sufficiently good evidence that their dissolution and dilution is reliable and good, then the whole method, end-to-end, is good.
Given that you're starting with a lot of solid and 1% is the expected analyte, you'd see, physically, if anything went wrong during dissolution (you'd see left-over solid). If anything went wrong in dilution, you'd also see it at that sort of level (if it sticks to surfaces, or precipitates); the sort of thing that frightens me in dilutions isn't the 1%, it's the 1pM solution which manages to find an active site on a piece of glassware and disappears completely.
We have to be able to believe in our ability to dissolve and dilute a solid, otherwise we wouldn't be able to quantify anything that's sold only in solid form, because we couldn't even trust ourselves to make the calibration standard.

[Simon001]

Dear lmh,

thank you so much for your reply, making me more confident to continue my analysis using standard addition.

We used to analyse this chemical using LCMS, but because of its high concentration in the sample, we have to dilute the extract a lot (more than 10,000 times). We are concerning such a high dilution factor may introduce more uncertainties in the quatitation (I might be wrong at this point). So we are thinking of using LC-DAD, which has lower sensitivity and lowers the dilution factor.

When I read some papers about the standard addition approach, all the papers mentioned to add the standard into original samples. But the problem is that the available standard in solution and its concentration is much lower than that in my sample. This brought up my question: if I can add standard after my sample is diluted 10 times for quatitation.

Thanks again for your reply. I appreicate it!

[Consumer Products Guy]

I'd pursue the LC-DAD route myself.

[Simon001]

We have DAD detector in our lab but have never tested with the chemical i am working on.