# Pressure in Skoog Instrumental Analysis Problem 27-22b (gas chromatography)

Problem 27-22b in:

Skoog; Holler; Crouch. Principles of Instrumental Analysis. Thomson Brooks/Cole (publisher varies by country)

A compressibility factor, $$j$$ is needed to compute them.

Answers that I find online all get $$j = 0.915$$, and a dead volume $$V_M$$ of $$\pu{8.3 mL}$$, which agrees with the solution in the back of the book. However they seem to use a unit conversion factor of $$\pu{5.17 torr psi-1}$$, which is off by a factor of $$10$$.

In my analysis $$\frac{P_i}P$$ should be ($$\frac{\pu{2.727 bar} }{\pu{0.997 bar}}$$), $$j$$ should be $$0.500$$, and $$V_M$$ should be $$\pu{4.5 mL}$$.

Am I wrong?

27-22

A GC column was operated under the following conditions:
Column: 1.10 m ✕ 2.0 mm, packed with Chromosorb P: weight of stationary liquid added, 1.40 g; density of liquid, 1.02 g/mL
pressures: inlet, 26.1 psi above room; room, 748 torr
measured outlet flow rate: 25.3 mL/min
temperature: room, 21.2°C; column, 102.0°C
retention times: air, 18.0 s; methyl acetate, 1.98 min; methyl propionate, 4.16 min; methyl n-butyrate, 7.93 min
peak widths of esters at base: 0.19, 0.39, and 0.79, respectively

Calculate
(a) the average flow rate in the column.
(b) the corrected retention volumes for air and the three esters.
(c) the specific retention volumes for the three components.
(d) the distribution constants for each of the esters.
(e) a corrected retention volume and retention time for methyl n-hexanoate.

• I'm not at all familiar with chromotography, could you add some calculations so that those of us not famliar are more able to chime in? – A.K. Nov 7 '18 at 15:06
• Page 197, slideshare.net/LEANNEDESOUSA/… – Martin Nov 8 '18 at 14:10