[Golden_4_Life]

I had a HPLC chromatogram result with peak  height = 9.3 centimetre
Retention time = 14.20 mins.
Width at baseline of peak = 7.4 centimetre

According to my chem book reference the formula: 16 x (T/W) quantity squared = theoretical plates. Yet the result I get is 58.98. This value seems very low as the book shows examples where the N,plates equals 5,000 to 9,000 values. Yet, I only get 59. Evidently, I must've made a wrong math turn somewhere? But I subbed the values in properly to my best knowledge.

[Golden_4_Life]

Now I get a value of 4,442 plates.
Presumably this sounds more reasonable.

[JGK]

You have to convert the width in cm to a value in time based on your chromatogram scale.

[Golden_4_Life]

JGK: I measured the width in "cm"; then measured how many cm it takes for the chrom to traverse 2 mins.  This gave me distance per time factor.

[JGK]

Is the formula in your original post correct or should it be N= 16 (RT/W)²

I can't calculate anything because I dont know the time scale (cm/sec or cm/min) of your Chromatogram.

[Golden_4_Life]

I certainly do not mean to mis-state anything here, but is not the formula using 5.5 instead of 16? and is it not 1/2 Width instead of total width?
I realize I could be inserting ''foot into mouth" here but I gotta clarify!

[JGK]

I certainly do not mean to mis-state anything here, but is not the formula using 5.5 instead of 16? and is it not 1/2 Width instead of total width?
I realize I could be inserting ''foot into mouth" here but I gotta clarify!

It' s N= a (t_r/W)²

where
a=16  peak width measured tangential (13.5% peak height) 
a = 5.54 peak width measured at half peak height
a = 25 peak width measured at 4.4% peak height (5s Method)

Personally, I've always used the half peak height method.

[Golden_4_Life]

OK, now this truly clarifies, thanky JGK.
I will aim to post up a chrom result so that this issue can be visualized.
I am told, via ''tribal knowledge" that a plate value of > 4000 is the criterion; is this tribal knowledge applicable here?   :delta: