[krees]

Hi
I have a dry practical write up, and i'm stuck with one of the questions.

METHOD
The absorption of a solution of haemoglobin (0.11 g/L) in distilled water was recorded at 20
nm intervals from 340 nm to 540 nm using a spectrophotometer. The spectrophotometer
was zeroed at each wavelength using a cuvette filled with distilled water only. The
absorbance measurements were repeated over the same range of wavelengths but at 10
nm intervals, to give a second spectrum.

the results were that the maximum absorption for the first measurement was an absorption of 0.52 at 400nm, and for the second an absorption of 0.58 at 410 nm.

the question is to discuss why these readings are different, but I have no idea

please help, it's due in tomorrow

thanks kacey

[Arkcon]

OK.  Let's look at the procedure, and your results.  Lambda max for the second trial is 410 nm.  What reading did you get at 410 nm for the first trial?  FWIW, I know the answer to this question, just by looking at your procedure.  Its not a clean-cut answer, as in a number.  But it is an answer, that explains the purpose of doing it this way.  As for the intensity difference, there's another answer, likewise non-quatitative, but still, important.  Another thing to consider -- what should max absorbance be?  Is it correct to assume that a sample always give the exact same absorbance, for every sample, every time, in every instrument?

[krees]

hi, thanks for replying, I don't have a reading for measurement 1 at 410nm, but, i have readings for 400nm, measurement 1 0.52, measurement 2 0.54, and then at 420nm, measurement 1 0.45, measurement 2 0.47

and i suppose they wouldn't be exactly the same but i'm not sure why?

[Yggdrasil]

What factors do you know affect the absorbance of hemoglobin?  How might these factors change over the course of the experiment?

[Arkcon]

hi, thanks for replying, I don't have a reading for measurement 1 at 410nm, but, i have readings for 400nm, measurement 1 0.52, measurement 2 0.54, and then at 420nm, measurement 1 0.45, measurement 2 0.47

and i suppose they wouldn't be exactly the same but i'm not sure why?

Try plotting your data on a chart, use two different colors for the two different "resolutions" chosen for this experiment.  Try to interpolate to see what's missing and see if it becomes clearer for you.