Calibration curve points range problem

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

4 posts Page 1 of 1
Dear All,

I have read in some scientific papers that:

The concentrations of the calibration curve should be evenly spaced over the chosen concentration range.

However, I am normally making the serial dilutions in this order: 100 ppb to 50ppb-25ppb-12.5ppb-6.25ppb-3.125ppb-1.56ppb-0.78ppb-0.39ppb-0.195ppb-0.0975ppb. But I realized that these data points dont have the same density. What do you think about my ranges? is this acceptable?

May I ask what do you recommend? I was thinking about having the data points like 100ppb-90ppb-80ppb-70ppb-60ppb-50ppb-40ppb-30ppb-20ppb-10-0.1ppb.

May I ask if this is acceptable? My problem with this new range is that even though they are evenly distributed but I may get a problem with finding my limit of detection at lower concentration because there are not so many points below 1 ppb whereas in the first example I have enough data points below 6.25 ppb which could help me to correctly find my limit of detection by visual inspection of the peaks.

May I ask what is your recommendations? I am really confused.

Thank you with your answers in advance

Best
Kourosh
In my opinion, if you are to choose the range and spacing of the calibration points yourself, take the application and the technique into account.

Generally speaking, if calibration ranges are relatively narrow (for example, 1-50ppm) in a method with linear responses (HPLC-UV, RI,..) it makes sense to have evenly spaced calibration => 1-10-20-30-40-50. Especially if the analyte is to be expected in the samples between these amounts.

On the other hand, in large calibration ranges (for example, 1ppb - 1000ppb) in a method with more quadratic response (LCMS) i'd chose relatively more points on the lower side => 1 - 5 - 20 - 100 - 500 - 1000. Especially if it's a contaminant analysis and most samples are negative or have low amounts of analytes.

I hope this makes sense and i'm interested what other posters have to say.

On a side note: do you really use 11 calibrations points?
Hi,

In fact, I am working with LC-Qtrap-MS 3200 Sciex. Yes, I am always using 11 calibration points. Do you think it is too much?

It seems to me that 1-5-20-100-500-1000 calibration points are not evenly distributed. Is it acceptable?

I am referring from this website

https://sisu.ut.ee/lcms_method_validati ... ation-data

“the concentrations should be approximately evenly spaced over the chosen concentration range, to ensure that different parts of the calibration graph are covered with approximately the same density of data points”
I develop methods in a private lab for routine environmental and food analysis. We typically use 5-6 calibration points, do not randomize them in between samples, and do not inject them in duplicate ..

I think the link you refer to is giving guidelines to perform a method evaluation, which is a test taking place in between the process of development and validation.
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