Stas-Otto separation gang

In analytical chemistry, the Stas-Otto separation process , along with other separation processes, is a qualitative process for the wet-chemical separation of pharmaceuticals. It was first described by Jean Servais Stas around 1850 and reworked into a more applicable form by Friedrich Julius Otto .

Separation principle

Because of their chemical structure, medicinal substances have different acidity or basicity , so that they are dissociated to different degrees in an acidic or basic environment. Accordingly, they either pass into an aqueous phase or into a phase of an organic solvent which is immiscible with this phase. This in turn can be influenced by setting the pH between 1 and 12.

method

The following analysis was modified by Harry Auterhoff and Karl-Artur Kovar . The substances of the six fractions obtained can be further differentiated by means of thin-layer chromatography , IR spectroscopy or clear color reactions.

Take up 30–100 mg of substance in 1.5 ml of water ( neutralize with 8% NaHCO ₃ solution if necessary ); Acidify with 3 N - H ₂ SO ₄ (approx. 10 drops) to pH 1 and then make up to 3 ml with water

Shake out with 3 × 5 ml of ether

Ether extract from sulfuric acid medium; Acids, phenols, ureals and neutral substances

Neutralize the aqueous phase with 15 drops of 8% NaHCO ₃ solution and adjust to pH 4–5 with 5 drops of 10% tartaric acid solution

Shake out 2 ml of 0.5 NaOH with 3 N

Shake out with 3 x 5 ml IBMK

II : IBMK extract from tartaric medium; weak bases, IBMK-soluble acids, phenols, neutral substances

Acidify the aqueous phase with 25 drops of 3 NH ₂ SO ₄ and shake out with 3 × 5 ml of ether

Ether phase

alkalize to pH> 10 with 3 drops of NaOH

IA : acids, phenols, ureals

IB : neutral substances

Shake out with 3 × 5 ml ether and 1 × 5 ml IBMK

III : ether from a sodium-alkaline medium; Bases

Neutralize with 3 drops of 3 NH ₂ SO ₄ and bring to pH 9 with 6 N- NH ₃

Shake out with 3 x 5 ml IBMK isopropanol ( 3 + 1 )

IV : IBMK isopropanol extract from an alkaline ammonia medium; Phenol bases, IBMK isopropanol-soluble bases

aqueous phase

V : substances that cannot be shaken out; Acids, ( sulfonamides ), carbohydrates , amino acids , quaternary ammonium compounds

Remarks

↑ instead of 3 ml, a total volume of 1 ml is sufficient for detection by thin layer chromatography; The amount of substance must then be reduced accordingly
↑ for an exhaustive extraction in this and in the following steps it is better to use 5 × 3 ml, see Nernst's distribution coefficient
↑ Pay particular attention to the exact setting of the pH value
↑ IBMK is the most polar solvent that does not mix with water; for substances that do not dissolve well in water or ether
↑ difficult separation of substances in II and III; possibly contain substances in both fractions
↑ This step is necessary for a better result when using thin layer chromatography
↑ Pay particular attention to the exact setting of the pH value
↑ amphoteric substances; pure IV fraction is difficult to obtain because the pH value of the individual substances is specific and therefore difficult to adjust; exhaustive extraction not possible here; Substances from IV therefore usually also in V

Examples

In the following some examples of drugs assigned to the respective group of the separation process:

IA : acetylsalicylic acid , diclofenac , methylparaben , phenylbutazone
IB : benzocaine , cholesterol , menadione , nifedipine
II : caffeine , theophylline
III : atropine , quinine , chloroquine , propranolol , tramadol
IV : allopurinol , atenolol
V : ascorbic acid , citric acid , methionine

literature

Harry Auterhoff, Karl-Artur Kovar, Claus OL Ruf: Identification of medicinal substances: Stas-Otto-Gang, thin-layer chromatography, color reactions, UV and IR spectroscopy, DC-UV coupling; 14 tables . 6., completely reworked. Ed. Wiss. Verl.-Ges, Stuttgart 1998, ISBN 3-8047-1554-0 .

Individual evidence

↑ Harry Auterhoff, Karl-Artur Kovar, Claus OL Ruf: Identification of medicinal substances: Stas-Otto-Gang, thin-layer chromatography, color reactions, UV and IR spectroscopy, DC-UV coupling; 14 tables . 6., completely reworked. Ed. Wiss. Verl.-Ges, Stuttgart 1998, ISBN 3-8047-1554-0 , p. 41 .

[2] stead of 3 ml, a total volume of 1 ml is sufficient for detection by thin layer chromatography; The amount of substance must then be reduced accordingly

[3] r an exhaustive extraction in this and in the following steps it is better to use 5 × 3 ml, see Nernst's distribution coefficient

[4] Pay particular attention to the exact setting of the pH value

[5] IBMK is the most polar solvent that does not mix with water; for substances that do not dissolve well in water or ether

[6] ult separation of substances in II and III; possibly contain substances in both fractions

[7] This step is necessary for a better result when using thin layer chromatography

[8] Pay particular attention to the exact setting of the pH value

[9] teric substances; pure IV fraction is difficult to obtain because the pH value of the individual substances is specific and therefore difficult to adjust; exhaustive extraction not possible here; Substances from IV therefore usually also in V

[1] Harry Auterhoff, Karl-Artur Kovar, Claus OL Ruf: Identification of medicinal substances: Stas-Otto-Gang, thin-layer chromatography, color reactions, UV and IR spectroscopy, DC-UV coupling; 14 tables . 6., completely reworked. Ed. Wiss. Verl.-Ges, Stuttgart 1998, ISBN 3-8047-1554-0 , p. 41 .