Precision of retention time

[Tonydatiger]

Hello,

First of all english is my second language. So it might be a little sloppy.

Anyhow im working on a pretty big project for school. Im analysing the pigments in algae with HPLC and for the peak identification I dont use standard but I compare classes of algea with eachtoher. For example if I analyse the algea 'synechococcus' I know I can espect 3 peaks from 3 pigments. When I analysed synechococcus I found the following retention times.

for Zeaxanthin 11,049
for Chlorophyll a 19,467
for Beta-Carotene 23,827

If I analyse a other algea that also got the pigment zeaxanthin I can be sure that the peak around 11m corresponds for Zeaxanthin.These are the retention times that I found;

11,106
11,049
11,019
11,113
11,107

but can I calculate a 95% Confidence interval for Zeaxanthin cuz I make a assumption on the algea that I analysed. Its not like a measured a zeaxanthin standard so can I still calculate a 95% Confidence interval.
So the question is; How can I calculate the precision of the retention time of zeaxanthin.

[rb6banjo]

I'm not exactly sure what you are after here but precision speaks to the repeatability of your measurement - in this case the retention times of the pigments.

For your retention times, the mean value is 11.081 minutes and the standard deviation is 0.044 minutes. That means the 95% confidence interval is 0.12 minutes (0.044*2.776 = 0.12, rounded to the meaningful number of digits). The value 2.776 comes from the t-table for 4 degrees of freedom at 95% confidence. To assign the identity of the peak in your extract(s) as Zeaxanthin it must elute between 11.0 and 11.2 minutes. Outside of that range, you must consider the fact that the pigment might be something else.

Does this make sense to you?