How to measure peak heights from a chromatogram?

[boysenberry]

In the Heinemann 2 Chemistry textbook, particularly chapter 6, there are a few questions asking to find the peak heights observed from a chromatogram from different known standards and comparing it to other samples for analysis. In these questions they seem to give the concentration of the standards concerned, however they do not give their peak heights. I've tried using a ruler and measuring the peaks but they don't seem be to scale. Anyway, I just quickly read the chapter today, so I'm not too confident. How can you tell the peak height of whatever your measuring?

[jimmy999]

Well you would actually have to use a ruler to measure them unless the computer you record them onto tells you the height.

One thing you should note is that it actually isn't the peak height that determines the concentration of the solutions. It's actually the area underneath the peaks. Generally the higher peak the greater the area therefore the greater the concentration which is why they sometimes say peak height even though it's not the correct measurement. The actual peak area is measured using integration which obviously isn't used in 3/4 Chemistry. So they should just tell you the peak area

[boysenberry]

Okay, how about question 14 in the review section of chapter 6. Question 14a asks you to find the peak heights of known standards. It shows this as a chromatogram. However, when you try to measure the heights with a ruler they're completely different to what's on the worked solutions.

Here's the link to the worked solutions:
http://vcenotes.com/forum/index.php/topic,20788.0.html

There is also another example in the book in page 69-70 that shows a chromatogram that I see as not making sense (at least to me). Using a ruler didn't work in this example also in finding the peak heights of the sample.

[boysenberry]

Well you would actually have to use a ruler to measure them unless the computer you record them onto tells you the height.

Thanks for the help so far but sorry, I still don't understand. I got the question wrong doing that.

[jimmy999]

Well you would actually have to use a ruler to measure them unless the computer you record them onto tells you the height.

Thanks for the help so far but sorry, I still don't understand. I got the question wrong doing that.

Ok maybe the answers are done as percentages or something like that. I'm on dialup speed so I can't exactly look at the question nor the solutions.

Alternatively the peak heights are measured in different units than cm/mm. In reality, the heights just need to be ratios of each other, which is actually the most likely solution

[Mao]

Well you would actually have to use a ruler to measure them unless the computer you record them onto tells you the height.

One thing you should note is that it actually isn't the peak height that determines the concentration of the solutions. It's actually the area underneath the peaks. Generally the higher peak the greater the area therefore the greater the concentration which is why they sometimes say peak height even though it's not the correct measurement. The actual peak area is measured using integration which obviously isn't used in 3/4 Chemistry. So they should just tell you the peak area

Actual practice actually doesn't pay that much attention to how large the peak area is, but rather the ratio of areas. In all samples/standards, you will have a reference with a fixed concentration, and you find the ratio of the area of the compound against this reference. This is because the machine won't always spit out the same area even if you have the same amount, due to differing conditions (slight variations in temperature, pressure, etc, otherwise known as random errors).