Hi everyone!
I'm trying to analyze vitamin C in several species of capsicum.
Beside using different extraction methods and considering all the cares needed to protect Vit C from degradation I get very low results (9mg/100g compared to other references 200mg/100g). In order to overcome this problem I'm trying to quantify vitamin C with the standard addition method but a question appears: I have different capsicum species, therefore, different matrixes, do I need to build a calibration curve for every specie? That sounds obvious but considerin that there are many different species, is there any other option?
I really appreciate all experiences and knowledge shared.
Thank your very much
Dear Carlos,
Even tough they're different capsicum samples (and hence diffeent matrices) they're all capsicum and thus the same species, so not so different after all.
My suggestion is you go ahead with your plan and in case you have samples outside (above or bbelow) the cal curve then adapt and re-build your cal curve accordingly. Building a cal curve for each and every capsicum species seems too much work for little gain.
Good luck,
Ana
Hi Carlos,
The standard addition method compensates and minimizes matrix effects by having the analyte and standard in the same matrix. Both must be equally affected by the matrix. However, care must be taken to ensure that the assay is performed within the linear regime. This is usually tested by adding the standard two or more times ("spikes") and noting the linearity of the analytical response/signal as a function of the total amount of standard added.
It should not matter if the matrix differs from one sample to the next.
If possible, extract the vitamin C under an inert atmosphere and avoid basic conditions.
- Hitoshi.
Dear Carlos, Standard addition method, by definition, is valid for only one particular sample. If you have 10 different samples, you need to make 10 different calibration curves in standard addition technique. Can you first establish from few preliminary studies that the standard addition method and external calibration give equivalent/acceptable results?
You did not mention which technique are you using to analyze Vitamin C. Are you taking all dilution factors into account? Getting 9 mg vs. 200 mg is a lot of difference.
Dear Carlos,
If you are using HPLC for the analysis, matrix effect will not be affected much in your analyis. So, irrespective of the capsicum species, you can try standard addition in one matrix. You can compare the results with titrimetric method (AOAC 985.33).
Good luck,
Pratheesh
Dear Carlos Abc ,
I think you have a good number of good answers, especially the assistant
given to you by Simona Gabriela Bungau . in my answer I just like to assure you that, one important advantage of Standard Addition is the nearly illimination of matrix fffect error. Although your samples and their matrices are different but you have always subtraction of the matrix effect between the standards and that particular samle. That means, just to make it clear, if the 1st. matrix is x1- x1= zero, for the second sample
x2-x2= zero also and so on. I just advise you not to change anything, such as the addition quqntity, or number of additions or at different times and temprature and so on. Please give importance to all the answers you have got and make a correct bdcision. Thank You and Good Luck.
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