Question

A note of caution concerning the GC data software: This software produces a tabulated summary of the peak retention times, peak areas, and peak area percentages for each chromatogram. Those percentages are not unique to any specific compounds, but rather they are expressed as fractions of the sum of all detected peak areas. For the calculations necessary to this exercise, new peak area percentages will need to be calculated for only the oxygenates peaks in your chromatograms and your calculations based upon those new percentages.

Two tables of GC peaks, identified by their associated gasoline component(-s), are presented below. Table 1 gives the results of an analysis of a gasoline mix without any “spike” (a “spike” is an addition of a known quantity of an analyte to a sample). Table 2 shows a GC analysis of the same gasoline mixture following the addition of 75 μL of pure methanol to a 1000 uL sample of the gasoline. Note two differences between the chromatogram peak areas; the methanol area increased from the spike (expected), and the other peak areas diminished.

Complete Table 3 by calculating the volume percentages of the six oxygenates in the 1000 μL of the original, unspiked gasoline sample from the observed changes in their peak areas following the methanol spike. To begin this calculation you will need to calculate the methanol GC response factor (μL / area count). Report this response factor in the indicated space on page 2. Report the original volumes of the oxygenates in the original, unspiked gasoline sample, and then report the oxygenates’ original concentrations as percentages of the whole unspiked 1000 μL gasoline sample.

Table 1: Unspiked Gasoline
Component	Area Counts	Area %
Pentane	236000	22.8404
Methanol	57	0.0055
Hexane	312100	30.2055
Ethanol	3200	0.3097
Isopropanol	563	0.0545
Cyclohexane	180111	17.4314
n-Butanol	2000	0.1936
di-n-Butyl Ether	360	0.0348
Benzene	73000	7.0650
Heptane	35001	3.3874
Isooctane	110111	10.6567
n-Pentanol	5100	0.4936
Toluene	6732	0.6515
Ethylbenzene	53211	5.1498
m- and p-Xylenes	11011	1.0657
o-Xylene	4700	0.4549
Totals	721603	100

Table 2: Methanol-Spiked Gasoline
Component	Area Counts	Area %
Pentane	219535	21.2469
Methanol	783	0.0758
Hexane	290326	28.0981
Ethanol	2977	0.2881
Isopropanol	524	0.0507
Cyclohexane	167545	16.2152
n-Butanol	1860	0.1801
di-n-Butyl Ether	335	0.0324
Benzene	67907	6.5721
Heptane	32559	3.1511
Isooctane	102429	9.9132
n-Pentanol	4744	0.4591
Toluene	6262	0.6061
Ethylbenzene	49499	4.7905
m- and p-Xylenes	10243	0.9913
o-Xylene	4372	0.4231
Totals	671989	100

Table 3: Gasoline Oxygenates Assay
Component	Volume (μL)	Volume Percentage
Methanol
Ethanol
Isopropanol
n-Butanol
di-n-Butyl Ether
n-Pentanol

Methanol GC Detector Response (μL/area count) = _______________