ISO 3987 Petroleum products - Lubricating oils and additives - Determination of sulfated ash
5 Reagents
For the analysis described in this International Standard, use only reagents of recognized analytical reagent grade and water complying with the requirements of grade 3 of ISO 3696:1987.

5.1 Low-ash mineral oil, white oil having a sulfated ash content (determined as follows) lower than the limit capable of being determined by this International Standard.

Determine the sulfated ash of the oil by the procedure given in Clause 8, but using 100 g of white oil, weighed to the nearest 0.5 g, in a 120 ml to 150 ml platinum dish. Deduct the sulfuric acid blank as described in 8.11.

5.2 Sulfuric acid (H2SO4), concentrated, 98 % minimum purity.

CAUTION - Sulfuric acid is highly corrosive, a strong oxidizer, and has a high heat of hydration. Protective clothing, including gloves and face mask, should be worn during operations involving this acid.

5.3 Sulfuric acid (1 + 1), prepared by slowly adding one volume of the concentrated acid (5.2) to one volume of water.

CAUTION - Mixing sulfuric acid into water generates considerable heat. When necessary, cool the solution before adding more acid. Do not allow the solution to boil. Never add the water to the acid.

5.4 Propan-2-ol, 99 % minimum purity.

CAUTION - Propan-2-ol is flammable, and can be explosive when evaporated to dryness.

5.5 Toluene, 99 % minimum purity.

CAUTION - Toluene is flammable and toxic.

6 Apparatus
6.1 Evaporating dish or crucible, made of porcelain, fused silica or platinum, of 50 ml to 100 ml capacity. For samples yielding less than 0.2 % (m/m) sulfated ash, use a platinum evaporating dish or crucible of 120 ml to 150 ml capacity. Do not use a platinum vessel if the sample is known to contain elements, such as phosphorus, which are injurious to platinum.

6.2 Electric muffle furnace, capable of maintaining a temperature of 775 °C +/- 25 °C and preferably having apertures at the front and rear to allow a slow natural draught of air to pass through the furnace.

6.3 Balance, capable of weighing to 0.1 mg.

6.4 Cooling container, without desiccant.

6.5 Filter paper, 0.01 % (m/m) ash maximum.

7 Samples and sampling
Samples shall be taken in accordance with ISO 3170, ISO 3171 or an equivalent national standard. The sample shall be thoroughly mixed before removal of the laboratory test portion.