ISO 3170 Petroleum liquids - Manual sampling
9 Sample handling
9.1 General
9.1.1 The method of handling samples between the point at which they are extracted or drawn and the final laboratory analysis of the test portion (or sample storage) shall ensure that the nature and integrity of the samples are maintained.

9.1.2 The method of handling a sample will depend on the purpose for which it has been taken. The laboratory analytical procedure to be used will often require a special handling procedure to be associated with it. For this reason, consult the appropriate method of test so that any necessary instructions as to sample handling can be given to the person drawing the sample. If the analytical procedures to be applied have conflicting requirements, draw separate samples and apply the appropriate procedure to each sample.

9.1.3 Take particular care in respect of the following:
a) liquids containing volatile components, since loss by evaporation can occur;
b) liquids containing water and/or sediment, since separation tends to occur in the sample container;
c) liquids with potential wax deposition, since deposition can occur if a sufficient temperature is not maintained.

9.1.4 When making up composite samples, take great care not to lose light ends from volatile liquids, and not to alter the water and sediment contents. The preparation of composite samples without loss of sample integrity is a very difficult operation and shall be avoided if possible.

9.1.5 Do not transfer samples of volatile liquids to other containers at the sampling location but transport them to the laboratory in the original sample container, cooled and inverted, if necessary. Great care is necessary if a sample contains both volatile components and free water.

9.2 Homogenization of samples
9.2.1 Introduction
Procedures are specified for the homogenization of samples that may contain water and sediment, or are in any other way non-uniform. Homogenization is required before any transfer of a partial quantity of sample, such as subsampling or removal of a test portion. Care is required to ensure that the homogenization process does not in itself cause a loss of representativity, such as through the loss of light components. Procedures for verifying that the sample is satisfactorily mixed before transfer are given in 9.3.

It is not possible to manually agitate samples of liquids containing water and sediment sufficiently to disperse the water and sediment within the sample. Vigorous mechanical or hydraulic mixing is necessary in order to homogenize the sample prior to transfer or subsampling.

Homogenization may be by various methods and will be governed by the sample, the sample receiver and/or the test method(s) used. Whichever method is used, it is recommended that the homogenizing system produces water droplets of sufficiently small size to ensure homogeneity and stability during subsequent handling, subsampling and analysis procedures.

The water content of stable emulsions containing small water droplets cannot be analysed accurately by centrifuge test methods. Alternative methods, such as ISO 10336, ISO 10337 and ISO 9029, should be used.

9.2.2 Homogenization by high-shear mechanical mixer
9.2.2.1 Fixed volume sample receivers
Insert a non-aerating high-shear mechanical mixer into the sample container so that the rotating element reaches to within 30 mm of the bottom.

NOTE 1 A mixer with counter-rotating blades operating at about 3 000 r/min is usually suitable. Other designs may be used if the performance is satisfactory (see 9.3).

In order to minimize loss of light ends from crude oils or other samples containing volatile components, operate the stirrer through a gland in the closure of the sample container. Mix until the sample is completely homogenized. A mixing time of 5 min is sometimes sufficient, but the size of the container and the nature of the sample affect the homogenization time. Verify that the sample has become homogeneous (see 9.3). Optimize the mixing conditions as necessary to achieve homogeneity and enable representative subsampling.

NOTE 2 High-shear mixers frequently produce stable emulsions, and water contents cannot be determined by the centrifuge method (ISO 3734).

Avoid any significant rise in temperature (> 10 °C) during the mixing. If feasible (7.2.3.2), it may be desirable to cool the sample prior to homogenization and/or during the homogenization.

9.2.2.2 Variable volume sample receivers
Operate the integral internal mixing system in accordance with the manufacturer's recommendations. Verify that the mixing conditions used are capable of homogenizing typical samples by conducting controlled injection/recovery tests (9.3). Optimize the mixing conditions as necessary to achieve homogeneity and enable representative subsampling.

Avoid any significant rise in temperature (> 10 °C) during the mixing. If feasible (7.2.3.2), it may be desirable to cool the sample prior to homogenization and/or during the homogenization.

9.2.3 Circulation with external mixer
External circulation may be applied to both permanently sited sample containers and portable containers; for the latter, use a quick-disconnect coupling. The method may be equally applicable to certain designs of variable volume sample receivers as well as larger fixed volume sample receiver/containers.

Circulate the contents externally using a small pump through a static mixer or spray bar mechanism installed in the piping. Various designs are available; follow the manufacturer's operating instructions.

The hold-up volume of the external mixer, pump and connections should be kept to the absolute minimum. This is to minimize the increase in the ullage volume within a fixed volume receiver during mixing, and thus minimize evaporative losses to the ullage space.

Use a circulating flow rate that is sufficient to theoretically circulate the total sample volume at least once per minute. A typical mixing time is 10 min, but this will vary according to the water content, the type of hydrocarbon components present in the product, the re-circulation flow rate, the total sample volume and the design of the system. Verify that the mixing conditions used are capable of homogenizing typical samples by conducting controlled injection/recovery tests (9.3). Optimize the mixing conditions as necessary to achieve homogeneity and enable representative subsampling.

Avoid any significant rise in temperature (> 10 °C) during the mixing. If feasible (7.2.3.2), it may be desirable to cool the sample prior to homogenization and/or during the homogenization.

When the whole sample is thoroughly mixed, run off the required quantity of subsample from a valve in the circulating line or from valves on the sample receiver, whilst the pump is running. Alternatively, subsamples may be taken via a syringe septum port (located downstream of the static mixer) while the sample is being recirculated.

If further subsamples are required on a later occasion, the contents of the external mixing loop shall be displaced back to the sample receiver/container on completion of subsampling, otherwise the remaining sample shall be transferred to a suitable secondary receiver/container for retention or disposal as necessary.

After use, the mixing loop shall be thoroughly cleaned with appropriate solvent(s), and then dried with compressed air. Care is required to ensure that there is no risk of the next sample being contaminated by the incorporation of residual sample or cleaning solvents that were held-up within the mixing loop.

NOTE The original empty container may be used to re-circulate solvent through the external mixing loop to clean it.

9.3 Verification of mixing efficiency
9.3.1 General
Whatever means are chosen for obtaining a subsample from a non-homogeneous mixture, verify the suitability of the mixing technique and the time required to obtain a homogeneous sample that can be representatively subsampled.

9.3.2 Homogeneous liquids
If the sample remains homogeneous and stable after mixing (e.g. where completely miscible components such as lubricant additives have been blended), continue the mixing procedure until successive samples drawn from the main bulk of the sample give identical results. This establishes the minimum mixing time.

NOTE As the sample is homogeneous after this time, and will remain so, transfers from the main bulk can be made without further mixing.

9.3.3 Non-homogeneous liquids
If the sample does not remain homogeneous for more than a short period of time after mixing (e.g. if water and sediment are part of the mixture), use the method for the verification of mixing efficiency described in 9.3.4.

NOTE It may be necessary, owing to the components present in the product, to subsample while mixing is still in progress.

9.3.4 Mixing efficiency verification test for non-homogeneous oils (injection/recovery test)
9.3.4.1 Weigh an empty receiver/container using a balance with sufficient resolution to enable the added water content (9.3.4.5) to be determined to 0.01 % (m/m) or better.

NOTE The procedure is equally applicable to fixed volume sample receivers and to variable volume sample receivers.

9.3.4.2 Fill the receiver/container with the typical expected sample quantity, using the actual liquid that is to be sampled. The suspended water content of this liquid shall, if possible, be less than 0.1 % (m/m), but the liquid used shall have no free water present. Record the liquid temperature.

9.3.4.3 Mix the simulated sample using the anticipated typical conditions (mixer rotational speed, mixing time, recirculation flow rate, number of mixing elements, recirculation time, mixing pressure differential and number of shuttles, etc.). Verify that the mixing has not caused the oil temperature to increase by more than 10 °C.

9.3.4.4 Using a dry syringe, subsample and analyse by Karl Fischer titration (ISO 10336, ISO 10337) to determine the baseline water content. Repeat the subsampling and analysis, and confirm that the results agree within 0.02 % (m/m). If the results fall outside this repeatability criterion, increase the severity of the mixing conditions (within the maximum temperature-increase limitation) and re-test until the results agree within 0.02 % (m/m). Alternatively, use a more efficient mixing system.

9.3.4.5 Reweigh the receiver/container and contents to determine the quantity of baseline oil that is present. Add a weighed quantity of distilled water to increase the total water content (baseline plus added water content) to a target level of at least 2 % (m/m) higher than the maximum concentration that is anticipated in actual samples. If the maximum anticipated concentration is unknown, add sufficient water to bring the total target water content to a minimum of 5 % (m/m).

9.3.4.6 Record the wet oil temperature prior to mixing the simulated sample using the same mixing conditions that were used to obtain the repeatable baseline analysis (9.3.4.4). Verify that the mixing has not caused the oil temperature to increase by more than 10 °C.

9.3.4.7 Subsample the mixed sample immediately using a dry syringe, and analyse the subsample by the same Karl Fischer titration to determine its water content. On completion of this analysis, repeat the subsampling and analysis step to assess the repeatability of the results and the stability of the emulsion created by the chosen mixing conditions.

9.3.4.8 Check the repeatability of the duplicate results, and the agreement between the mean water content found (9.3.4.7) and the total target water content (baseline plus added water content) (9.3.4.5). The maximum permissible range (X) of the duplicate results and the maximum permissible difference between the mean result and the target result (Y) shall not exceed the tolerances given in Table 3.

9.3.4.9 If the injection/recovery test criteria (Table 3) are met, use the proven mixer conditions for all subsequent subsampling of the same source sample with the same or lesser water content.

9.3.4.10 If the measured water contents do not meet these criteria, repeat the procedure with a fresh sample, but increase the severity of the mixing conditions (e.g. the mixing time and/or speed, flow rate) until the criteria are met or the sample temperature increase restriction is exceeded.

If the injection/recovery test criteria are still not met, re-test using a modified mixing procedure such as remixing immediately prior to taking the second subsample, or taking all subsamples while mixing continuously. Alternatively, use a different type of sample mixing system.

If the sample temperature increase restriction is exceeded, consider pre-cooling the sample or cool the sample during mixing where this is practical (7.2.3.2).

9.3.4.11 Do not attempt to subsample crude oil or other non-homogeneous oil samples for water and sediment content analysis unless the representative conformity of the sample mixing and subsampling procedures have been proven by this procedure.

9.3.4.12 Do not determine water content by the centrifuge method (ISO 3734 or ISO 9030) for this verification of the mixing system, as the method cannot be relied upon to give the total water content.

9.4 Transfer of samples
9.4.1 Transfer of sample between receivers/containers shall, if possible, be avoided unless conducted under controlled conditions. If the primary sample cannot be transported directly to the laboratory, it shall be transferred completely to a secondary container that can be transported directly to a laboratory. A complete transfer may be difficult due to evaporative loss of light components and/or the incomplete transfer of heavier components. In such circumstances, a sampling method shall be used that will permit the primary sample to be delivered to the laboratory without any transfer or subsampling. If this is not possible, any sample handling and/or transfer outside of controlled laboratory conditions shall be kept to the absolute minimum.

9.4.2 At every stage involving partial transfer of a sample, it is essential to homogenize the contents of the container from which the sample is being taken using one of the methods specified in 9.2.

9.4.3 Verify the mixing efficiency for each combination of container and mixer by one of the methods specified in 9.3.

9.4.4 Complete any transfer of sample within the period during which the mixture is known to be homogeneous. In some cases (especially during subsampling into more than one container), it may be necessary to continue mixing during the transfer operations.

10 Sampling of tank residues/deposits
Samples of tank residues/deposits are unlikely to be representative and shall only be used for guidance regarding their nature and composition.

Select an appropriate sampling device, depending upon the dimensions of the gauging access point(s) available and the depth of the residue/deposit to be sampled. (See 5.2.4 and Figure 8.) Follow the manufacturer's instructions and transfer the sample from the device into a metal, plastics or glass container, which shall maintain the integrity of the sample.

NOTE Tank residues are organic and/or inorganic sediments forming a layer on the bottom of either marine or land-based tanks. At ambient temperatures, the product is highly viscous and of a soft to stiff consistency.