Spectroscopy Lab Conceptual Question

[jxs919]

Can someone explain why an absorbance maxium is always used for an assay. What problems would occur if an absorbance minimum were used to get an Absorbance spectrum of a solution?

thanks.

 

[GCT]

What is your analysis for this question with relevance to the reliability in the detection of the analyte as well as the reliability (precision) involved in the quantitative analysis?

 

[jxs919]

hmmm I'm not sure what yu're askin but i think the reliability in the detection of the analysis would be based on taking the absorbance of the solution several times and then comparing the values to a referenced value... right ?

i just don't understand why we have to use a max absorbance value...
why can't we do the minimum value...

help me out some more here ..

 

[GCT]

By "minimum" absorbance value, I'm assuming that there is another absorbance peak which has the smallest of the intensities, right? And, does this pertain to UV-Vis spectroscopy?

Quantitative analysis, such as when constructing a beer's law based calibration plot, is done using the maximum absorbance value, in particular, because it works well with the wavelength peak that has a high absorptivity at that wavelength. For the latest uv-vis spectrometers you want the absorbance peak to be between 1.0 and 3.0 absorbance units, and the peak should be pretty broad, assuming that all peaks have an ideal shape, the one with the highest intensity will be more reliable. The position of the peaks can shift at times, with broader peaks, the corresponding change in the intensity value will be less dramatic.

 

[jxs919]

ok yea i see what you mean now. awesome. thanks for your help.

 

[Gokul43201]

Can someone explain why an absorbance maxium is always used for an assay. What problems would occur if an absorbance minimum were used to get an Absorbance spectrum of a solution?

You'd compromise the signal to noise ratio.

 

[GCT]

Yeah, and that too, although this can also be a problem with high absorbance intensities when scattering is involved.