Summary

The weight percent of beta-pinene (b-p) in citrus oil samples was determined using gas chromatography (GC) analysis. 100 mL (.1) of standard 1 % b-p solvent was made by placing 1.0017 g (1) b-p in a 100.0 mL volumetric flask and adding methylene chloride to the mark. To four test tubes were added 500.0 µl (.5) of two different citrus oils: lemon oil was placed in tubes A1 and A2, orange oil in tubes B1 and B2. 1.0 mL (.001) of methylene chloride was added to all the tubes. Then 100 µl (.1) of the standard 1% solvent was added to tubes A2 and B2 to create spiked samples. Tube weights were measured when the tubes were empty and again after the addition of each substance (oil, methylene chloride, and solvent).

The GC instrument was programmed with the settings specified in the lab manual. GC runs were collected for the standard 1% solvent solution and each of the four test tubes, the results shown in Table 2. The 1% solution showed a peak 3.172, and the orange oil showed a peak at 3.365, indicating b-p.

Using the B2 3.365 peak and the B1 2.760 peak, the weight percent was determined to be 0.98% of b-p in orange oil (see Table 1). As no peak registered for the lemon oil in the 3.000-3.999 range, the b-p weight percent was not determined. Given the available data, a Ttest was not calculated.

Calculations

Standard's concentration (Cs) = .07428 M, calculated as follows:
1.0017 g b-p * (mol/136.24g) = .007352 moles/ 0.1 L solvent = .07352 M

Standard's volume (Vs) = 100 uL
Unknown's volume (Vx) = 500 uL
Ration (R)= Inew/Istd, or Tube 2 / Tube 1
g oil = weight of tube with just oil - empty tube weight
Calculation to find unknown's concentration (Cx) is:
Cx = Cs * Vs/(R(Vs +Vx) - Vx)
 
Orange oil:
R = 3.365/2.760 = 1.0219
Cx = (.07352 M)(100 uL)/(1.0219(100 uL + 500 uL)- 500uL) = .06498 M b-p
.06498 M b-p (L/1000mL)(mL/1000uL)(500uL) = 3.249 x10-5 moles b-p
3.249 x10-5 moles b-p * (136.24g/mol) = .004426 g b-p
(.004426 g b-p/.454 g oil)*100 = 0.975 => 0.98% b-p
 
Lemon oil:
No b-p peak for A2 in the 3.000-3.999 range, thus this data is disregarded.