What causes the last two points of the spectrophotometry standard curve to be low, and how can this be avoided?
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I would like to ask the experts: What is the reason why the last two points on the spectrophotometry standard curve are low, resulting in a small slope and higher measured values? How can this be avoided?
Is the R value meeting the requirements? If not, redo the curve; once it meets the requirements, then we can discuss whether it’s too high
I have encountered this situation as well. 1. Pay attention to whether the reaction has completed under the given conditions; this is very important. That’s what happened to me, and I’m not sure if the same is true in your case. 2. Check whether there is enough of the reactants needed. 3. Issues with sample collection procedures
Reduce the concentration of the standard solution; the absorbance might be too high
The standard curve has a linear range, and the sample must be diluted to fall within this range for testing.
In general colorimetric analysis, as the concentration of the substance being measured increases, there is an appropriate limit for the amount of reagents such as color developers in the system; exceeding this limit causes the standard curve to deviate, which is a normal phenomenon. The sample can be appropriately diluted to fit the standard curve.
Deviations occur during the dilution of standard samples; for each diluted sample, the stock solution must be used.
Remove the last two points and add two points within the normal range at the beginning; when testing the sample, ensure that the concentration of the substance of interest in the sample falls within the normal range of the curve. Your standard value might be too broad.
This post was last edited by sunshineda_VGMP on 2018-6-16 21:08. A spectrophotometer is the instrument used in spectrophotometric analysis; by testing standard solutions at various concentration levels, the corresponding absorbance values are obtained, which are then used to create a series of standard curves showing concentration gradients. It generally consists of five points; the range for selecting these points should not be too wide, as this would cause the final points to deviate, nor should it be too narrow, as that would result in the high-concentration areas not being representative.