Propose a series of concentration to be used for calibration curve. If an unknown solution produced a result outside the range of the calibration curve, how could this be solved?
To propose a series of concentrations for a calibration curve, follow these steps:
1. Determine the range of concentrations you expect to encounter in your samples. Choose a series of concentrations evenly distributed throughout this range.
2. Start with a blank solution (no analyte) and then prepare a set of standard solutions by adding known amounts of the analyte to blank solutions.
3. Prepare a minimum of 5-7 standard solutions with different concentrations, spanning the expected range of the samples. For example, you might choose concentrations of 0, 5, 10, 15, 20, 25, and 30 ppm (parts per million).
4. Label the concentration of each standard solution accordingly.
5. Analyze each standard solution using the same method or instrument that will be used for sample analysis.
6. Plot a graph of the instrument response (such as signal intensity or absorbance) against the known concentrations. This is your calibration curve.
Now, if an unknown solution produces a result outside the range of the calibration curve, you have a few options to consider:
1. Dilution: If the concentration of the unknown solution is higher than the highest concentration in the calibration curve, you can dilute the sample to bring it within the range of the curve. Dilute the sample appropriately and reanalyze it using the same method or instrument. Then, calculate the concentration of the original undiluted sample using the dilution factor.
2. Higher concentration standard: If you anticipate samples with higher concentrations, you can prepare additional standard solutions with higher concentrations to extend the range of your calibration curve. Analyze these new standards along with the existing ones to update and extend your calibration curve. Then, you can reanalyze the unknown sample using the updated curve.
3. Lower concentration standard: Similarly, if the unknown solution has a lower concentration than the lowest concentration in your calibration curve, you can prepare additional standard solutions with lower concentrations. Analyze these new standards, update your calibration curve, and reanalyze the unknown sample accordingly.
It's crucial to have a well-validated calibration curve that covers the expected range of concentrations. This helps ensure accurate and reliable results for both known and unknown samples.