Elemental analysis

Question 1

What is elemental analysis?

Answer 1

Elemental analysis is an experiment that determines the amount (typically a weight percent) of an element in a compound.
It is the most reliable way of confirming that drugs are pure

Question 2

What are the most common types of elemental analysis?

Answer 2

 The most common type of elemental analysis is for carbon, hydrogen, and nitrogen (CHN analysis)

Question 3

What is elemental composition the same as?

Answer 3

Empirical formula

Question 4

What is the process of elemental analysis?

Answer 4

 Weigh accurately a small amount of the compound
 Burn it
 Capture all the elements as suitable oxides, e.g. H2O, CO2, NO2, SO2
 Measure the amount of each oxide present and calculate the % of each element in the drug sample
 Evaluate whether the analytical (experimental) results match what we expect for our drug

Question 5

What is the experimental procedure for elemental analysis?

Answer 5

 In the same machine, these gases are passed over a copper catalyst, which reduces the mixed nitrogen oxides to N2 and the mixed sulphur oxides to SO2
 The mixture of gases is then analysed by gas chromatography, using a thermal conductivity detector
 Carbon, hydrogen and nitrogen can be analysed simultaneously, but the analysis of sulphur is prone to inaccuracy if hydrogen is also being measured
 Halides and sulphur are analysed separately

Question 6

Example: theoretical elemental analysis of aspirin

Answer 6

Theoretical elemental analysis:
C9 = 12.01 x 9 = 108.09
H8 = 1.01 x 8 = 8.08
O4 = 16.00 x 4 = 64.0
Total molecular mass = 180.17

I.e. C = 59.99 %, H = 4.48 %

Question 7

What is an acceptable error for elemental analysis?

Answer 7

± 0.3 % is an acceptable error. If analytical results are within ± 0.3 % of the calculated figures, we can be confident of having the right and pure drug.

Question 8

working out consistent purity of samples…

Answer 8

C = 59.76 %, H = 5.30 %
Calculated elemental analysis for 100% Aspirin should give you the following figures:
C = 59.99 %, H = 4.48 %
Calculated error for carbon: 59.99% – 59.76% = 0.23%

Calculated error for hydrogen: 4.48% – 5.30% =-0.82%

Conclusion:
Although % value for carbon is within ± 0.3 % error limit, the experimental error for hydrogen exceeds an acceptable error limit of ±0.3 %
Aspirin in the analytical batch A-274 is NOT pure drug