Hi,

For determining sodium ion concentration in 20 percent Albumin, currently I am using dilutions of Na+ 1000 ppm standard solution (Thomas Baker) for preparing the calibration curve. I am currently using dilutions of the 20% percent sample directly without any prior extraction or any other preparative steps.

Since the composition of matrices of the standard preparation and the sample are completely different, I am not very comfortable with the process I am following. Can anyone suggest any idea how both the standards and the sample can be prepared such that this difference in matrix and any probable effects arising from it can be negated.

Thank you for posting on scientistsolutions.com.

I suggest that you use a technique called the "Method of Standard Additions." In this procedure, you spike a known volume of your sample with a known amount of standard. Then you analyze the unspiked sample and the spiked sample and compare the results. This is essentially a recovery experiment. You should be able to calculate the % recovery of the added standard, and it should be very close to 100 %. If not, then you have matrix effects and you must correct for them.

In the traditional Standard Additions experiment, you actually spike at three or more different concentrations, and plot the amount found against the amount added. The x-intercept for the regression line will tell you how much is in your sample. See the plot below; the amount in this sample would be 1.0.

Or, you can just use the following formula and average the results.

–QA = QS[RA/(R(A+S) -RA)]

where A is the unknown, S is the standard, Q is the quantity (mass or concentration units), and R is the response (area, height, etc.).