Write 2 pages with APA style on Determination of the relative proportions of caffeine and aspirin in proprietary analgesics by gas chromatography-mass spectrometry (GC-MS). From the graph of caffeine y = 513930X –5000000 From the table Y = 69124507.67 This implies that: 69124507.67 =513930X -5000000 X = (69124507.67+5000000)/ 513930

Thus x= 144.2307

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2. y= 13698X+84489

From the table Y = 3498180

This implies that: 3498180= 13698X+84489

X = (3498180-84489)/ 13698

Thus x= 249.21

From graph of ethyl-2-acetoxybenzoate

3. y = 540290X –4000000

From the graph Y = 71959867

This implies that: 71959867=540290X -4000000

X = (71959867+4000000)/ 540290

Thus x= 168.69

4. y= 38480X+33693

From the graph Y = 6270026

This implies that: 6270026= 38480X+33693

X = (6270026-33693)/38480

Thus x= 162.067

Why calibration standards are always analyzed in increasing order of concentration

Calibration in decreasing order of concentration would not give the exact concentration in the subsequent experimental analysis as some solution may remain in the apparatus.

SOURCES OF ERROR

1. Incorrect sampling

2. Incorrect integration – especially poor peak detection and false base line positioning.

3. Missing capacity control by statistics

LINEARITY OF CALIBRATION GRAPH

A plot of peak area/peak height vs. concentration gives a straight line graph described by the equation y =mx +c

Where y is the response of the instrument (analytical signal/peak area/peak height)

X is the concentration

M is the slope

C is the constant

From graph of peak area vs. concentration the value of R2 is 0.996 while the value of R2 from graph of peak height vs. concentration is 0.824.The difference is 0.172 implying a close fit.

For ethyl-2-acetoxybenzoate

. From graph of peak area vs. concentration the value of R2 is 0.998 while the value of R2 from graph of peak height vs. concentration is 0.994.The difference is 0.004 implying a close fit.

MAGNITUDE OF ERROR

From graph 1(caffeine)

Error value for calculating the sample concentration using peak area is given by the formula,

Error rate = (standard deviation for peak area/average of peak area) 100 %

Error rate = (1338029.784/69124507.67)100 %

Error rate for peak area = 1.9356

Error value for calculating the sample concentration using peak height is given by the formula,

Error rate = (standard deviation for peak height /average of peak height) 100 %

Error rate = (67277.17721/3498180)100 %

Error rate for peak area = 1.9232

The error for calculating sample concentration from peak area is 1.9356 and that for the sample concentration from peak height is 1.9232 there is only a very small difference of 0.0124. The magnitude of this error rate difference is insignificant

From graph 2(ethyl-2-acetoxybenzoate)

Error value for calculating the sample concentration using peak area is given by the formula,

Error rate = (standard deviation for peak area/average of peak area) 100 %

Error rate = (754485.1699/71959867)100 %

Error rate for peak area = 1.0485

Error value for calculating the sample concentration using peak height is given by the formula,

Error rate = (standard deviation for peak height /average of peak height) 100 %

Error rate = (58809.76655/6270026)100 %

Error rate for peak area = 0.938

The error for calculating sample concentration from peak area is 1.045 and that for the sample concentration from peak height is 0.938 there is only a very small difference of 0.107. The magnitude of this error rate difference is insignificant.

How to improve methods and result

Carefully rinse the volumetric flask to ensure correct and precise concentration

The sample should be carefully handled to avoid contamination.

Conclusion

The objective of this experiment is met. The concentration of the unknowns was found by interpolation using the graph of the known standards. This method may not be a perfect one but considering the error rate that occurred, it is still an appropriate method of determining the concentration of the unknowns.

Reference

Harris, Daniel Charles (2003). Quantitative chemical analysis. San Francisco: W.H. Freeman. .

Skoog, Douglas A.. Holler, F. James. Crouch, Stanley R.. (2007). Principles of Instrumental Analysis. Pacific Grove: Brooks Cole.

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