Qualitative test for CO toxicity

[a_zed24]

Hello there!
One quick (and relatively insensitive) method to detect acute CO poisoning is to take a blood sample, dilute it and mix it with 5% NaOH. A pink tint in comparison with the colour obtained from a normal blood specimen (I've been told it'd be brown-ish?) suggests the presence of carboxyhaemoglobin.
I've searched a lot but I couldn't find an explanation behind this test... Why will the addition of NaOH to blood containing CO make it pink? What's NaOH's role in all of this? Why's it NaOH and not something else?
Thanks a bunch in advance!

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[efle]

Looks like Oxy-Hg and CO-Hg have different absorbance in the 500s nm range, so normal blood in a highly basic prep will be the typical reddish/brownish while CO poisoned blood will appear a slightly different hue. Shouldn't matter whether it's NaOH or another source of OH

 

[NotAProgDirector]

I assume this is for some S1 question. In real life, the ABG oximeter will tell you the carboxyhemoglobin level in 10 seconds.

 

[a_zed24]

Looks like Oxy-Hg and CO-Hg have different absorbance in the 500s nm range, so normal blood in a highly basic prep will be the typical reddish/brownish while CO poisoned blood will appear a slightly different hue. Shouldn't matter whether it's NaOH or another source of OH

View attachment 297762

makes sense... thank you, it helped a lot!