Reference Samples and Data

Intro: 

You might remember awhile ago when I was testing the calibration of the machine by using a tile that contained 5 metal samples and a plastic sample. But, because m1y study focuses on both aqueous and soil samples, I need to test the limits of detection using liquid, certified reference materials. I have already tested lead, nickel, chromium, and cadmium using AA standards. I just bought arsenic, mercury, and antimony to test.

How checking the calibration of the machine works is by creating a sample in which you know the exact measurements in it. Using simple math you could calculate the ppm for an element you wish to put into a sample, measure it out in a syringe, and put it into the HNO3. Then when you run it through an x-ray analyzer, you would know what to expect for numbers. What we need to be cautious of is the LOD (limits of detection). The LOD tells us the lowest concentration (ppm) that an element can be examined in a sample. For my CRMs they are:

Sb= 6 ppm

As=.2 ppm

Hg=None

What this means is if I go below the LOD, the x-ray analyzer will not be able to pick up on the concentration. That is why we created a calibration sample that contains the following:

Sb= 9.89 ppm

As=10.10 ppm

Hg=10.04 ppm

Data:

A large concentration of the reference material was created.  I then put the reference material into four different measuring samples that were individually run through the x-ray analyzer. A total of nine data sets were collected throughout the four samples. The numbers calculated included:

Sb= 12.9, 13.3, 14, 13.3, 18.7, 14, 11.9, 16.1, 12.8 (ppm)

As= 2, 2.2, 2.2, 2.1, 2.2, 2.1, 2.3, 2.1, 2 (ppm)

Hg= 3, 3, 2.9, 2.6, 2.9, 3, 2.8, 3.1, 2.7 (ppm)

Conclusions:

The data does not seem very close to the expected values. Because of this, I now need to have the machine calibrated and adjust all values for experiments done.