| Features and benefits of non-aqueous titration |
- Extends the solubility range for substances insoluble in water (e.g. fats and oils)
- Extends the application range: weak bases and acids can be easily titrated
- Weak bases like aromatic amines or heterocyclic compounds with pKb values up to 12 can be titrated in organic solvents
- Weak acids with pKa values up to 12 can be titrated in organic solvents
- High accuracy in non-aqueous titrations can be reached by special monitoring of the titration conditions. Ambient
temperature is of special importance for solutions in non-aqueous titrations; organic solvents have a thermal coefficient of extension approximately 10 times higher than water, and a temperature difference of 1°C may cause an error of 0.3 %.
Acetic Acid
- Good solubility properties for most bases
- Gives distinct potential curves with clear endpoints
- Enables titration of weak bases with pKb values up to 12
- Simultaneous determinations are not possible (acetic acid has a leveling effect on weak bases)
Acetic anhydride
- Similar properties as acetic acid
- Superior for determination of weak bases (because it is free of water)
- Primary and secondary amines cannot be titrated (rapid acetylation)
Methanol
- Good solubility properties and does not cause indication problems
- Its titration behavior is very similar to water
- Only substances with pKb up to 9 can be titrated
Isopropanol
- High dielectric constant
- Low acidity
- Simultaneous determinations are possible
- Not recommended for very weak bases (pKb > 10)
Acetone
- Often used because it enables a very good differentiation of bases and shows sufficient solubility properties
- Perchloric acid is most commonly used as a titrating agent
- With glacial acetic acid as a solvent, perchloric acid in acetic acid is used (good storage stability)
- When using differentiating solvents like acetone or isopropanol, acetic acid interferes because of the leveling effect. Instead, perchloric acid in dioxan is recommended; it gives excellent titration results but is not stable for a long time. Perchloric acid in isopropanol is also recommended; it gives the same results as perchloric acid in dioxan and has a long storage time. For weak bases, applicability of isopropanol is limited.
Preparation of perchloric acid titrating agent
The FIXANAL concentrate of perchloric acid fluka 3206 has unlimited storage and can be used for preparation of a standard solution in the necessary solvent. It can be filled up to 1L to form a solution of 0.1 mol/L or filled up to any other volume for a desired concentration. Temperature must be taken into account when preparing the solution.
The FIXANAL concentrate of perchloric acid fluka 3206 has unlimited storage and can be used for preparation of a standard solution in the necessary solvent. It can be filled up to 1L to form a solution of 0.1 mol/L or filled up to any other volume for a desired concentration. Temperature must be taken into account when preparing the solution.
0.1 mol/L perchloric acid in glacial acetic acid
Fill up the content of FIXANAL concentrate of perchloric acid Fluka 32046 with acetic acid (min. 99.8%). This solution contains approx. 0.5 % water. If a water-free or lower-in-water titrating agent is needed, acetic anhydride can be added.
Fill up the content of FIXANAL concentrate of perchloric acid Fluka 32046 with acetic acid (min. 99.8%). This solution contains approx. 0.5 % water. If a water-free or lower-in-water titrating agent is needed, acetic anhydride can be added.
0.1 mol/L perchloric acid in dioxan
Before opening the FIXANAL ampoule Fluka 32046, fill approx. 500 mL dioxan in a volumetric flask and cool. Then open the ampoule, and swirl around the dioxan carefully, so the acid is diluted at once. Rinse the ampoule with dioxan and fill the volumetric flask up to the mark. This solution has limited stability for storage. It slowly takes up a brownish color. Addition of 1-2 % water increases stability but it may interfere when titrating weak bases.
Before opening the FIXANAL ampoule Fluka 32046, fill approx. 500 mL dioxan in a volumetric flask and cool. Then open the ampoule, and swirl around the dioxan carefully, so the acid is diluted at once. Rinse the ampoule with dioxan and fill the volumetric flask up to the mark. This solution has limited stability for storage. It slowly takes up a brownish color. Addition of 1-2 % water increases stability but it may interfere when titrating weak bases.
0.1 mol/L perchloric acid in isopropanol
Fill approx. 500 mL isopropanol in a volumetric flask. Open the FIXANAL ampoule Fluka 32046, and immediately swirl around the isopropanol to dilute the acid at once. Rinse the ampoule with isopropanol and fill the volumetric flask up to the mark with isopropanol.
Fill approx. 500 mL isopropanol in a volumetric flask. Open the FIXANAL ampoule Fluka 32046, and immediately swirl around the isopropanol to dilute the acid at once. Rinse the ampoule with isopropanol and fill the volumetric flask up to the mark with isopropanol.
- Enables determination of all acids up to pKa 11
- Stronger acids are leveled, below pKa 6 they cannot be differentiated anymore
- Equivalent points are very distinct
- Disadvantages: unpleasant odor and possible absorption of carbon dioxide from ambient air
- Excellent solvent for salts and for titration of acids
- Shows strong differentiation; only strong acids with pKa 0 are leveled
- Because of its low basicity the absorption of carbon dioxide is very little and does not cause problems
- Equivalent points are indicated clearly
- Note: after standing for some time, DMF can be hydrolyzed by strong acids causing interference in the titration curve
Isopropanol
- Good solvent for acids; it is differentiating up to pKa 0
- This solvent is not recommended for very weak acids (pKa 11)
Acetone
- Strongly differentiating; even strong acids like hydrochloric or perchloric acid can be separated
- Ideal solvent for simultaneous determinations and separations
- Most common titration agents are tetramethylammonium hydroxide (TMAOH) and tetrabutylammonium hydroxide (TBAOH); they are strong bases and soluble in organic solvents
- TMAOH is soluble in polar organic solvents. For example, the use of methanolic solutions can be limited due to the leveling effect of methanol. Mainly isopropanol-methanol mixture is used, which presents an acceptable compromise between storage and titration behavior. Solution in isopropanol with a smaller leveling effect is used especially for titration of very weak acids. A small content of water increases stability without influencing titration properties.
- TBAOH shows the same basicity in titration as TMAOH; however, solubility of tetrabutylammonium salts formed in the titration is favorable. Some tetramethyl compounds are poorly soluble and can coat the electrodes. TBAOH has a lesser storage stability compared to TMAOH.
- Fluka 38336 (concentrate) contains 0.1 mol TMAOH dissolved in approx. 20 mL water (aqueous solution ensures long storage stability). It can be filled up with the desired solvent to make 1L of 0.1 mol/L standard solution (or to any other volume based on the desired molarity).
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