ISO 10370 Petroleum products - Determination of carbon residue - Micro method
7 Sample preparation
7.1 General instructions
For samples which consist essentially of distillate material, either follow the preparation as in 7.2 or prepare a distillation residue following a modified procedure of ISO 3405, given in 7.3. This latter procedure uses 4 ml vials (6.1) and shall be used for middle distillate samples which may yield a carbon residue below 0.30 % (m/m).
7.2 Regular procedure
Thoroughly stir the sample to be tested, first warming if necessary to reduce its viscosity. If the samples are in liquid form, transfer directly to the vials (6.1) using a rod or syringe. If the samples are solid materials, they shall either be heated, or frozen with liquid nitrogen and then shattered to provide manageable pieces.
7.3 Modified procedure
7.3.1 Ensure that the 4 ml vials (6.1) are clean and stored in a desiccator (without desiccant) before use. Set up the distillation as described in ISO 3405 using a clean 125 ml flask with no carbon deposits and add six glass or ceramic "anti bumping" beads (1.5 mm to 2.5 mm diameter is recommended) to aid the mixing of residue as well as reducing bumping.
The thermometer may be omitted and replaced with a snug fitting, well rolled cork or silicone rubber stopper because it is the volume of distillate collected that is critical not the temperature of distillation. For an automatic unit, the temperature recording device may be necessary to allow the instrument to operate.
7.3.2 Discontinue heating when 88 ml of distillate has been recovered in the receiver. Allow the flask to cool for 5 min at the end of the distillation. Mix the residue in the flask by swirling. Immediately after mixing, transfer 2.5 ml to 3.0 ml to a pre-weighed vial of 4 ml (6.1) and reweigh. Take care to exclude any anti-bumping beads. This residue represents a 10 % (V/V) bottom portion of the original sample.
8 Sample transfer
8.1 During weighing and filling, handle the vials with forceps to minimize weighing errors. Discard the vials after use.
8.2 Weigh the clean sample vials, and record the mass to the nearest 0.1 mg.
8.3 Transfer an appropriate mass of the sample as indicated in Table 1 into the bottom of a weighed sample vial, taking care to avoid contact between the sample and the vial wall, reweigh to the nearest 0.1 mg and record. Place the loaded sample vials into the vial holder (up to 12), noting the position of each sample with respect to the index mark.
A control sample may be included in each batch of samples being tested. This control sample should be a typical sample which has been tested at least 20 times in the same equipment in order to define an average percent carbon residue and standard deviation.
Results for each batch are deemed acceptable when results for the control sample fall within the average percent carbon residue plus/minus three standard deviations. Control results which are outside these limits indicate problems with the procedure or the equipment.
