so gc can be used for both qualitative and quantitative analysis again your qualitative analysis is looking at identifying species so the retention times or volumes depending on what you're looking for are employed for identification so for instance let's say this is a standard sample of compound a and compound b you know exactly what those are where they're located when you run an unknown sample you can identify so you have to use the same exact conditions and then your retention time here will match up when you can identify compound a and compound b now one slight shifting issue you might observe is that your injection rate remember i said you put the syringe in it has to go in and out the same exact way so depending on how you inject each time will possibly shift these ever so slightly but it still should be noticeable within that region you can evaluate the purity of organic compounds or the effectiveness of purification can any contaminants in your sample will show as additional peaks so let's pretend this unknown sample was supposed to be a pure sample of a and b well obviously there's additional peaks so there's contaminants or whatever the case might be you can also use it to confirm the presence or absence of suspected species in a mixture you take an authentic sample add that to the mixture if no no peaks appear if no new peaks should appear if they do then obviously something's wrong there existing peaks should just be enhanced so if you weren't quite sure and you say well maybe that's a and maybe that's b what you would do is take another set of your sample add the standard to it that you know have a and b in it and then these peaks should be enhanced if you get additional peaks you have a problem but if you just see these peaks enhanced then that confirms that that's a and b so selectivity factor is going to depend on society factor here is kb over ka a these are distribution constants and that's going to be the retention time of b minus the dead time retention time of a minus the dead time which gives you tr prime b over tr prime a numerical tabulations of the selectivity factors for pure compounds relative to common standards can be prepared and used for characterization of solutes you can also use this for quantitative analysis so finding out how much of something you have the accuracy of this is within one percent real um relative attainability reliability directly related to the control variables and the nature of the sample the analysis is based on peak height so here again look at this here here's your peak height maximum this is going to be the so that would be maximum height this would be a height at half peak width so the peak heights are inversely related to the peak width this allows for accurate results obtained only if variations in the column conditions do not alter peak width the variabilities to control are going to be column temperature effluent flow rate the rate of sample injection so the rate of sample injection is going to lead to errors of 5 to 10 percent so here we're going to get errors of 5 to 10 you want to make sure you avoid overloading the column so you can't just inject an unlimited amount you have to inject a small enough amount to be detected but not overload the column the analysis can also be based on peak area and this is independent of broadening effects more satisfactory analytical variable than doing the peak height and do any of these you need to have calibration and standards so preparation of a series of standard solutions so just like we do calibration curves you're going to obtain peak height and plot as a function of concentration so it's just it's calibration curve but instead of using absorbance like we've done in the past for uv vis now you're using peak height or peak area depending on whatever you're looking at for the highest accuracy frequent re-standardization is necessary it is extremely important that your standards and your unknowns are run at the exact same time not days apart or not even hours apart and you frequently want to re-standardize as needed source of error is going to be uncertainty in the volume of the sample and the rate of injection