Decolourising Charcoal
(Ph. Eur. monograph 0313)
Action and use
Adsorbent.
DEFINITION
Obtained from vegetable matter by suitable carbonisation processes intended to confer a high adsorption power.
CHARACTERS
Appearance
Black, light powder free from grittiness.
Solubility
Practically insoluble in all usual solvents.
IDENTIFICATION
A. When heated to redness it burns slowly without a flame.
B. Adsorption power (see Tests).
TESTS
Solution S
To 2.0 g in a conical flask with a ground-glass neck add 50 mL of dilute hydrochloric acid R. Boil gently under a reflux condenser for 1 h, filter and wash the filter with dilute hydrochloric acid R. Evaporate the combined filtrate and washings to dryness on a water-bath, dissolve the residue in 0.1 M hydrochloric acid and dilute to 50.0 mL with the same acid.
Acidity or alkalinity
To 2.0 g add 40 mL of water R and boil for 5 min. Cool, restore to the original mass with carbon dioxide-free water R and filter. Reject the first 20 mL of the filtrate. To 10 mL of the filtrate add 0.25 mL of bromothymol blue solution R1 and 0.25 mL of 0.02 M sodium hydroxide. The solution is blue. Not more than 0.75 mL of 0.02 M hydrochloric acid is required to change the colour of the indicator to yellow.
Acid-soluble substances
Maximum 3 per cent.
To 1.0 g add 25 mL of dilute nitric acid R and boil for 5 min. Filter whilst hot through a sintered-glass filter (10) (2.1.2) and wash with 10 mL of hot water R. Evaporate the combined filtrate and washings to dryness on a water-bath, add to the residue 1 mL of hydrochloric acid R, evaporate to dryness again and dry the residue to constant mass at 100-105 °C. The residue weighs a maximum of 30 mg.
Alkali-soluble coloured substances
To 0.25 g add 10 mL of dilute sodium hydroxide solution R and boil for 1 min. Cool, filter and dilute the filtrate to 10 mL with water R. The solution is not more intensely coloured than reference solution GY4 (2.2.2, Method II).
Ethanol (96 per cent) soluble substances
Maximum 0.5 per cent.
To 2.0 g add 50 mL of ethanol (96 per cent) R and boil under a reflux condenser for 10 min. Filter immediately, cool, and dilute to 50 mL with ethanol (96 per cent) R. The filtrate is not more intensely coloured than reference solution Y6 or BY6 (2.2.2, Method II).
Evaporate 40 mL of the filtrate to dryness and dry to constant mass at 100-105 °C. The residue weighs a maximum of 8 mg.
Fluorescent substances
In an intermittent-extraction apparatus, treat 10.0 g with 100 mL of cyclohexane R1 for 2 h. Collect the liquid and dilute to 100 mL with cyclohexane R1. Examine in ultraviolet light at 365 nm. The fluorescence of the solution is not more intense than that of a solution of 83 μg of quinine R in 1000 mL of 0.005 M sulfuric acid examined under the same conditions.
Sulfides
To 1.0 g in a conical flask add 5 mL of hydrochloric acid R1 and 20 mL of water R. Heat to boiling. The fumes released do not turn lead acetate paper R brown.
Copper
Maximum 25 ppm.
Atomic absorption spectrometry (2.2.23, Method I).
Test solution: Use solution S.
Reference solutions: Prepare the reference solutions using copper standard solution (0.1 per cent Cu) R and diluting with 0.1 M hydrochloric acid.
Source: Copper hollow-cathode lamp.
Wavelength: 325.0 nm.
Atomisation device: Air-acetylene flame.
Lead
Maximum 10 ppm.
Atomic absorption spectrometry (2.2.23, Method I).
Test solution: Use solution S.
Reference solutions: Prepare the reference solutions using lead standard solution (100 ppm Pb) R and diluting with 0.1 M hydrochloric acid.
Source: Lead hollow-cathode lamp.
Wavelength: 283.3 nm; 217.0 nm may be used depending on the apparatus.
Atomisation device: Air-acetylene flame.
Zinc
Maximum 25 ppm.
Atomic absorption spectrometry (2.2.23, Method I).
Test solution: Use solution S.
Reference solutions: Prepare the reference solutions using zinc standard solution (100 ppm Zn) R and diluting with 0.1 M hydrochloric acid.
Source: Zinc hollow-cathode lamp.
Wavelength: 214.0 nm.
Atomisation: device Air-acetylene flame.
Loss on drying (2.2.32)
Maximum 15 per cent, determined on 1.00 g by drying in an oven at 120 °C for 4 h.
Sulfated ash (2.4.14)
Maximum 5.0 per cent, determined on 1.0 g.
Adsorption power
To 0.300 g in a 100 mL ground-glass-stoppered conical flask add 25.0 mL of a freshly prepared solution of 0.5 g of phenazone R in 50 mL of water R. Shake thoroughly for 15 min. Filter and reject the first 5 mL of filtrate. To 10.0 mL of the filtrate add 1.0 g of potassium bromide R and 20 mL of dilute hydrochloric acid R. Using 0.1 mL of methyl red solution R as indicator, titrate with 0.0167 M potassium bromate until the red colour is discharged. Titrate slowly (1 drop every 15 s) towards the end of the titration. Carry out a blank titration using 10.0 mL of the phenazone solution.
Calculate the quantity of phenazone adsorbed per 100 g of activated charcoal from the following expression: 2.353(a−b)/m
a = number of millilitres of 0.0167 M potassium bromate used for the blank;
b = number of millilitres of 0.0167 M potassium bromate used for the test;
m = mass in grams of the substance to be examined.
Minimum 40 g of phenazone is adsorbed per 100 g of activated charcoal, calculated with reference to the dried substance.
Microbial contamination
TAMC: acceptance criterion 10 CFU/g (2.6.12).
TYMC: acceptance criterion 10 CFU/g (2.6.12).
STORAGE
In an airtight container.
