A lesson in how to analyze gas chromatography (GC) lab results including peaks and percent composition of mixtures. Get the guide and sample lab report here: www.chemcomplete.com/product-...
Thank you so much! In just over 10 minutes, you taught me what a GCM was and how it worked as well as exactly what I needed to know to analyze the results which neither my teacher nor my textbook nor my TAs could do for me so thank you again
when you describe the matching of peaks to boiling points, you put a dash in between y and z and their boiling points but not x. this makes it look like they are negative (-82 and -37) while x is positive.
Really good video man! I was just wondering is it possible to use this method with a unkown sample withouth having ms or lc. And do you need to have the boiling point for all the molecules in you sample you testing before using this method ?
How did you get the precise areas? Is there a table in MestreNova that shows the peak width and exact intensity that can then be used to calculate the area? Thanks
Shouldn't the x and y be swapped over? The peak is high so I'd of thought x would be in the second highest peak? I thought it goes in order of boiling points to high and low peaks. If that makes sense
May I know how to calculate the area of the peak, as in real graph, the peaks are not very sharp as triangle where we could apply triangle area formula. Kindly let me know from where will I get the area of the peaks.
Good video. A point to be noted: different compounds yield different peak area even if they have the same concentration; e.g. 100ppm of X, 100ppm of Y, 100ppm of Z will not yield the same peak area. Taking only the areas to calculate selectivity/composition could yield wrong results. The compounds need to be calibrated and their respective concentrations should be used to calculate composition and selectivity.
Thanks really helpful, but if we have 2 compounds that have similar boiling point 1 cis and 1 trans which one has the lower retention time? Appreciate your feedback. Thanks
great explanation! a little feedback... for the visual learners it would help to add a diagram of the standard gas chromatography setup, while youre explaining how the gas is passed through the coils. and put it next to the graph while youre explaining that the nonpolar parts are expelled first.
what if there is 3 possible products but the GC data only show 2 peaks what does that mean, how do I know which one is which one and what is present of not
How can we calculate the %yield of our product in reaction mixture using GC-MS, With or without taking any internal or external standard. Can anyone help??
To use this 'simplistic' method, you must make it clear that you have assumed or confirmed that the 3 components have similar (even the same) response factors in the particular detector being used.
This is true and does need to be accounted for in more complex lab work and mixtures. This video is aimed at students first experiencing GC labs in general or organic chemistry. It would not be appropriate to teach response factors until an upper level course such as instrumental chemistry or an advanced spectroscopy course.
He wrote the "-" as a reference to connected it to y. It's confusing because he didn't do it for "x". But it's meant just to show y - 82 to show that y is 82 (it is not -82).
Hi, not the OP here, but doing GC lab work is my job, and generally speaking, if you expect a certain Rtime and your results show an Rtime higher than control (or reference), then you are looking at a similar, but ultimately different compound. RE: THC vs synthetic cannabinol
No. "retention time" peaks is what you get from the GC. m/z is what you get from the mass spectrometry after the GC. It relates to the fractionation of the compounds into their fraction ions which is related to the mass to charge ratio of each ion that fractions from a given compound
You first draw a baseline (you would not use the x-axis line).Then you would measure from the top of the peak to the baseline to get the height and then to get the width, you would go to the halfway point on the height and then measure the width from there. So, the equation would be A= H x W(1/2) if that makes sense.
Dude, I _knew_ this instrument had to be set up to give you the integral. Idk why but our professor has us doing this some weird way where we estimate the integral by printing it out and physically measuring height and width to get a rectangular approximation. Why? Why couldn't I just be given data if the instruments give you data? And if we're going old school, why not cut out the peaks and weigh them? At least that method is cool.
This can depend on the GC being used, but generally it is the area of the x and y axis units. So most GC will have minutes (retention time) along x and a volts (detector signal) on the y axis. So a common unit might be volts-minute.
This does not seem right to me. Your calculation assumes the same detector response to all compounds. However this is not true. 50/50 % mixture does not generally make 50/50 % response. I would say you need to know the response factors to make the calculation.
