Yes! Raw material purity information is recorded on the certificate of analysis. Restek’s Quality Control (QC) lab confirms the chemical identity and purity of mixture components and solvents using two or more of the following techniques: GC-FID, HPLC, GC-ECD, GC-MS, LC-MS, refractive index, and melting point. Compounds with a listed purity of less than 99% have been weight corrected to compensate for the presence of extraneous impurities in the compound, inorganic moieties (salts, hydrates, etc.), and organic moieties (typically the functional group of a derivatized compound). To better illustrate these scenarios, the following examples will explain the process we apply:
Example 1 – Purity adjustment
Compound A is tested and found to contain a 2% impurity (compound B). That is, the purity of compound A is 98%. So, if 100 mg is weighed out, the material will contain 98 mg of compound A and 2 mg of compound B. Adding 100 mL of solvent will produce a concentration of 980 µg/mL for compound A, not the desired 1,000 µg/mL. To reach a concentration of 1,000 µg/mL for compound A, Restek chemists apply a correction factor of 0.98 to obtain the final concentration:
100 mg ÷ 0.98 = 102 mg
- Using the following calculation will result in 100 mg of compound A being added to the solution and the desired concentration of 1,000 µg/mL:
(102 mg ÷ 100 mL) x 1,000 = 1,020 µg/mL x 0.98 = 1,000 µg/mL compound A
Example 2 – HCl adjustment
Compound A is the hydrochloride salt of an organic amine. If the molecular weight of compound A is 100 AMU, then the molecular weight of the parent compound (organic moiety) would be 63.5 AMU—molecular weight of compound A minus molecular weight of HCl. The ratio of organic moiety to inorganic moiety would be:
63.5 ÷ 100 = 0.635
If 100 mg is weighed out, the material will contain 63.5 mg of the parent compound and 36.5 mg of HCl. Adding 100 mL of solvent will produce a concentration of 635 µg/mL for the parent compound, not the desired 1,000 µg/mL. To reach a concentration of 1,000 µg/mL for the parent compound, Restek chemists apply a correction factor of 0.635 to obtain the final concentration:
100 mg ÷ 0.635 = 157.5 mg
- Using the following calculation will result in 100 mg of compound A being added to the solution and the desired concentration of 1,000 µg/mL:
(157.5 mg ÷ 100 mL) x 1,000 = 1,575 µg/mL x 0.635 = 1,000 µg/mL parent compound
Example 3 – DNPH adjustment
Compound A is the dinitrophenylhydrazone (DNPH) derivative of a carbonyl compound. If the molecular weight of compound A is 250 AMU, then the molecular weight of the parent compound (carbonyl moiety) would be 70 AMU—molecular weight of compound A minus molecular weight of DNPH moiety. The ratio of carbonyl moiety to carbonyl DNPH moiety would be:
70 ÷ 250 = 0.28
If 100 mg is weighed out, the material will contain 28 mg of the parent compound and 72 mg of DNPH. Adding 100 mL of solvent will produce a concentration of 280 µg/mL for the parent compound, not the desired 1,000 µg/mL. To reach a concentration of 1,000 µg/mL for the parent compound, Restek chemists apply a correction factor of 0.28 to obtain the final concentration:
100 mg ÷ 0.28 = 357.1 mg
- Using the following calculation will result in 100 mg of compound A being added to the solution and the desired concentration of 1,000 µg/mL:
(357.1 mg ÷ 100 mL) x 1,000 = 3,571 µg/mL x 0.28 = 1,000 µg/mL parent compound
