Analytical measurements are an important part of science. There are many instrumental methods that lend themselves to measuring the concentration of a given element or compound. Some methods, such as UV-VIS, IR, NMR, and EPR require a standard of known concentration, or a concentration curve, to measure the concentration of an unknown. In this laboratory exercise, students create a calibration curve and "unknown" samples. The data can be evaluated, and the precision of EPR analysis is compared to other instrumental methods.
There are two basic methods for determining concentrations from EPR data: One is using peak to peak amplitudes, and the other is using double integral values. The microESR processing software will calculate both values (peak to peak amplitudes are easily read). The peak to peak amplitude method is quite straight forward, and the measured amplitude is proportional to the concentration.
The double integral method is more complicated because the baseline is very important when calculating the double integral values (see the microESR Processing and Analysis Software manual). It is also critical where the points to cut the integral are picked as any baseline without signal will add noise, but the double integral value should also be proportional to the concentration.
It is very important when making the standard solutions that you record the exact mass of solid. This experiment uses volumetric pipettes to "measure" the water to make the solutions. What would be a better way to "measure" the water? When using a volumetric pipette, the pipette should be calibrated. How would you calibrate the pipette?
