Question

Mg standard	Absorbance	%RSD
0.5	0.09533	0.3
1	0.1209	0.2
2	0.17304	0.3
5	0.28137	0.2
10	0.56901	0.5
20	0.87153	0.3
5 mL Unk	0.14296	0.2

[1] Make a calibration curve using the absorbances for the samples from 0.5 – 20 ppm. Include the intercept (0,0) as a data point.

[2] Is the calibration linear, i.e., does the analysis follow Beer’s law? To discuss linearity, examine both the trend of the data relative to the least squares line and the correlation coefficient.

[3] Use a 2nd order polynomial (in Excel’s plotting function) to determine if the fit improves and include this curve.

[4] Explain why AAS often has a limited linear dynamic range compared to say, UV/VIS and fluorescence spectrophotometry

Answer 1

Answer 1:

The calibration curve from the given data is as follows:

Answer 2:

Calibration graph is not exactly linear. However, one can say that it follows Beer - Lambert's Law.

The calibration curve addins trend line as follows with least square line equation.

Answer 3:

Yes, the second order polynomial is much improved the fit as follows.

Answer 4:

UV-visible is a "base" tool. It's the best way of understanding the simple concept of quantitative spectroscopy is that something absorbs light so to measure how much of that "something" you have, you can determine it is based on how much light was absorbed. UV-visible basically does this by sending the right wavelength out, and then measuring the absorbance. Works on pretty much anything where you're measuring the concentration of it.

AAS is a modification/specialisation of UV-visible. It's far more accurate, because it doesn't send out a band of wavelengths (even if you "select" a wavelength with UV, you still send out a range of them, for example all the red wavelengths might range from 600 - 650 nm). But AAS sends out the EXACT wavelength that gets absorbed by that substance.