I am trying to calibrate a GC in my lab and I am completely new at using one. I have ran a cylinder of known concentrations (100 ppm) of Acetaldehyde, Acrolein, Propylene Oxide, Propanal and balance N2 through the GC 3 times and got the retention time and area for each peaks. Now I am a bit lost about how to draw the calibration curve for the obtained effluent peaks.
- Learning how to initially operate a GC system and run an analysis method should be done under the supervision of someone trained in how to use the system. Please have someone at your school assist you with this assignment.
Note: The "GC" is not calibrated, the specific method used is. A proper scientific "calibration" procedure will use a standard measured at multiple concentrations, not one. Try and gather multiple points of data for each standard across the expected concentration range of test samples. Use at least five different concentration values per order of magnitude (more is often better). Once you have collected and integrated the data from each analysis, use the GC software to create a multilevel calibration table to plot the data (Peak height vs concentration. Determine y=mx + b). If you do not have any GC data analysis software, then you can simply use some graph paper or a statistical or spreadsheet program (i.e. Microsoft EXCEL). This procedure will be repeated for each analysis standard, but if the compounds can all be resolved using the same GC method , then you can create one multilevel calibration table for ALL standards (which will save time).
YouTube has many videos on calibration curves. Use Excel as the curve is linear (y=mx+b). The x-axis is concentration (ug/mL or ng/mL) and the y-axis is peak area. Inject the standards 3 times using 6 different levels of concentration. Use the average and the standard deviation to calculate the LOQ. Confirm this LOQ with the S/N (signal/noise) ratio.
Muntaseer
For sure you need to read some book on basics of GC.
Regards
GB
Muntaseer Bunian , I am sure the GC is operated with a chromatography control software. Beside taking Bruce Neagle 's advice of studying the fundamentals of calibration and how to properly construct the calibration function (!) - it's all no rocket science, just a little math involved, and Bruce is right! - the way I started - eons back - was taking out the manual and read. In many cases the manuals are great starting points. And I agree with William Letter that your supervisor is needed to step in.
On the other hand: at the beginning of scientific live there is study! ;-)
Keep up, read, try, fail and get up again!
Cheers,
Detlef.
How about asking your prof at the university or take a class of quantitative chemistry?
William has already explained at length. I have only one point to add. When you are plotting the graph, you can plot peak area against concentration instead of peak height. Both are correct, but peak area is widely used. Rest everything you can do as suggested by William.
Peak height will be fine for this type of simple experiment (and is more common with many cap GC methods run by new users). Area is of course fine, but as Bunian is a student, I prefer to keep the advice simple and measuring peak height requires little effort, with less chance of integration error (something a new user will not know how to do yet).
In order to prepare calibration curve, it is advisable to prepare the calibration standard at least 5 levels, the LCL should be at or below the LOQ levels. Each levels should be injected 3 times. Then, you may prepare easily the calibration curve based on the area derived from each of the injected calibration concentration. Using the GC software, you may easily prepare this curve. alternatively you may prepare the calibration curve based on the area and the concentration of the injected compound.
Best of luck..
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