chromatography experiment

8/12/2019 Chromatography Experiment

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alter peak width during the period required to obtain chromatograms for sample and standards. The variables that must

be controlled closely are column temperature, eluent flow rate, and rate of sample injection.

Peak area: Peak area is independent of broadening effects caused by the variables mentioned in the previous paragraph

From this standpoint, therefore, area is a more satisfactory analytical parameter than peak height. On the other hand,

peak heights are more easily measured and, for narrow peaks, more accurately determined. A simple method that work

well for symmetric peaks of reasonable widths is to multiply peak height by the width at one-half peak height.

Calibration with standards: The most straightforward method for quantitative chromatographic analyses involves the

preparation of a series of standard solutions that approximate the composition of the unknown. Chromatograms for the

standards are then obtained, and peak heights or areas are plotted as a function of concentration. A plot of the data

should yield a straight line passing through the origin; analyses are based on this plot. Frequent standardization is

necessary for highest accuracy.


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Results of the Experiment

1. Photosplease see below. The pen marks are Sharpie: 1=S, Crayola: 2=C, Vis--Vis: 3=V2. Rf valuesplease see the attached lab notebook3. a. i. Ink from Vis--Vis separated well in 25% ethanol. Ink from Crayola was beginning to separate

towards the top, but the separation didnt complete, and the edges were not well defined. Ink from Sharpie

spread out into a dark purple shade, without clear boundaries. These data points indicate Crayola is the mostpolar, followed by Vis--Vis, with Sharpie not very polar.

ii. In 95% ethanol, Sharpie was beginning to demonstrate separation into components the bestamongst the three and had travelled the farthest. Vis-a-Vis was beginning to separate out, but had not travelled

at all. Similarly, Crayola did not travel far and separation into components did not occur (although signs of blue

had begun to appear towards the top).These data points indicate Sharipe is the most non polar, with Crayola

being the most polar.

b. We had used the green Crayola marker which separated into yellow right away when placed in 25% ethanol,

with almost no signs of blue. When placed in 95% ethanol, separation only began to occur towards the end,

where signs of blue were visible, but no indication of yellow. This would suggest that yellow is less polar due to

its visibility and lack of travel in 25% ethanol, and that blue is highly polar as it travelled the farthest in both thesolutions


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Post-Lab Questions

1. If left for too long in the beaker, the paper may have undistinguishable streaks or be blank. The sample inkswould travel through the length of the paper due to capillary action, and determining distance of the solvent

front would be difficult, making the Rf calculations unreliable, if at all possible.

2. Increasing the length of the paper would result in better chances for the components to parse out. This wouldbe at the expense of time.

3. The farther the pigment from the starting line, the more non polar it is. Stationary phase is polar, and anypigments that stop travelling indicate their polar nature. Mobile phase tends to be more nonpolar than water.

4. It will be interesting to see how three different (markers) filter papers in the same beaker behave. These filterpapers would be longer than the ones used in this experiment. This could lead to less smearing and possible

better indication of pigments. Also, a mechanism (clamp?) to hold the filter paper(s) vertical will allow the

pigments to reach the solvent front uniformly.

chromatography experiment

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