Sulphated ash procedure as per BP / IP | Residue on ignition procedure as per USP | Sulfated ash test method | Sulfated ash formula |
The Residue on Ignition/Sulfated Ash test uses a procedure to measure the amount of residual substance not volatilized from a sample when the sample is ignited in the presence of sulfuric acid according to the procedure described below. This test is usually used for determining the content of inorganic impurities in an organic substance.
Sulfated ash – As per British Pharmacopoeia (Appendix IX A)
The amount of substance used for the test (usually 1-2 g) is chosen so that at the prescribed limit the mass of the residue (usually about 1 mg) can be measured with sufficient accuracy.
Method I :
Heat a platinum dish to redness for 10 minutes, allow to cool in a desiccator and weigh (W1). Unless otherwise specified in the monograph, place 1.0 g of the substance being examined in the dish (W2) , moisten with sulfuric acid, ignite gently, again moisten with sulfuric acid and ignite at about 800°C. Cool, weigh again as W3, ignite for 15 minutes and repeat this procedure until two successive weighing’s do not differ by more than 0.5 mg.
Calculate the percentage of residue by the equation.
W3 – W1
% of Ash = —————- x 100
W2 – W1
Method II :
Ignite a suitable crucible (for example, silica, platinum, porcelain or quartz) at 600°C ± 50 °C for 30 min. allow cooling in a desiccator over silica gel and weigh note down the weight as W1. Place 1 gm of the sample in the same crucible and weigh. Note down the weight as W2. Moisten the sample with a small amount of sulfuric acid (usually 1 ml) and heat gently at as low a temperature as practicable until the sample is thoroughly charred. After cooling, moisten the residue with a small amount of sulfuric acid (usually 1 ml), heat gently until white fumes are no longer evolved and ignite at 600°C (± 50°C) until the residue is completely incinerated. Ensure that flames are not produced at any time during the procedure. Allow the crucible to cool in a desiccator over silica gel, weigh it again. Note down the weight as W3.
Calculate the percentage of residue by the equation.
W3 – W1
% of Ash = —————- x 100
W2 – W1
If the amount of the residue so obtained exceeds the prescribed limit, repeat the moistening with sulfuric acid and ignition, as previously, for 30 min periods until 2 consecutive weighing do not differ by more than 0.5 mg or until the percentage of residue complies with the prescribed limit.
Conduct the ignition in a well-ventilated hood, but protected from air currents.
Acceptance criteria: Specified in monograph
Residue on ignition – As per United States Pharmacopeia (281)
Ignite a suitable crucible (for example, silica, platinum, quartz, or porcelain) at at 600°C ± 50 °C for 30 min. allow cooling in a desiccator over silica gel and weigh note down the weight as W1. Place 1.0 gm of the sample (or the amount specified in the individual monograph) in the same crucible and weigh. Note down the weight as W2. Moisten the sample with a small amount of sulfuric acid (usually 1 ml) and heat gently at as low a temperature as practicable until the sample is thoroughly charred. After cooling, moisten the residue with a small amount of sulfuric acid (usually 1 ml), heat gently until white fumes are no longer evolved and ignite at 600°C (± 50°C) until the residue is completely incinerated. Ensure that flames are not produced at any time during the procedure. Allow the crucible to cool in a desiccator over silica gel, weigh it again. Note down the weight as W3.
Calculate the percentage of residue by the equation.
W3 – W1
% of Ash = —————- x 100
W2 – W1
If the amount of the residue so obtained exceeds the prescribed limit, repeat the moistening with sulfuric acid and ignition, as previously, for 30 min periods (note down the weight as W4) until 2 consecutive weighing do not differ by more than 0.5 mg or until the percentage of residue complies with the prescribed limit.
Conduct the ignition in a well-ventilated hood, but protected from air currents.
Acceptance criteria: Specified in monograph
Sulfated ash – As per Indian Pharmacopoeia (2.3.18)
Heat silica or platinum crucible to redness for 10 minutes, allow to cool in desiccator and weigh. Note down the weight as W1. Place 1 gm (or the amount specified in the individual monograph) of the sample in the crucible and weigh. Note down the weight as W2. Ignite, gently at first, until the substance is thoroughly charred. Cool, moisten the residue with 1 ml of sulphuric acid, heat gently until the white fumes are no longer evolved and ignite at 800° ± 25° until all black particles have disappeared. cool, weigh it again. Note down the weight as W3.
Repeat the moistening with sulfuric acid and ignition, as previously, for 15 min. periods (note down the weight as W4) until 2 consecutive weighing do not differ by more than 0.5 mg.
Calculate the percentage of residue by the equation.
W4 – W1
% of Ash = —————- x 100
W2 – W1
Acceptance criteria: Specified in monograph
