BS 16166:2021 pdf download – Soil, treated biowaste and sludge — Determination of adsorbed organically bound halogens (AOX)
8 Sample storage and pretreatment
8.1 Sampling and storage
For the sampling and storage of sludge samples, refer to existing standard, e.g.  and . Samples shall be stored in suitable containers with an appropriate closure material such as PTFE. Samples to be frozen may be stored in aluminium containers pre-cleaned by heating to 450 °C for minimum 4 h or by rinsing with a non-chlorinated solvent.
Samples shall be kept at a temperature of (5 ± 3) °C and in the dark.
The sample pretreatment for sludge samples should take place within 24 h of sampling. Alternatively, samples can be frozen (−18 ± 3) °C) directly after sampling and kept frozen for a maximum of one month before sample pretreatment.
8.2 Sample pretreatment
Pretreat the samples according to EN 16179 , if not otherwise specified. Cool the dried test sample in a desiccator, comminute and homogenize in an analytical mill or porcelain mortar (7.3.4) to a particle size of no more than 0,1 mm. Store the ground material in a desiccator or a tightly closed glass container.
The homogenised wet sample portion may alternatively be freeze-dried, which in some cases makes homogenizing of the dried sample easier.
The test portion taken for analysis shall have an AOX value within the working range of the instrument.
NOTE A typical working range is between 1 µg to 30 µg chlorine (absolute titrated amount).
9.2 Adsorption and inorganic halide removal Ensure that the dried, ground test sample is homogenized by stirring or shaking before taking the test portion.
Prepare the test portion for combustion as follows:
— Transfer a homogenized test portion of 10 mg to 100 mg depending on the expected AOX content to a conical flask or screw cap vial (7.2.3).
— Add approx. 20 mg activated carbon (6.1) and 10 ml nitrate stock solution (6.7) to the sample. The amount of activated carbon shall be the same for all test samples, blank determinations, etc.
— Shake for 1 h using a mechanical shaker (7.2.4).
— Filter the suspension through a filtration apparatus (7.2.1) using nitrate washing solution (6.8).
Wash the filter cake with small amounts of nitrate washing solution.
Use a total volume of 25 ml to ensure complete transfer.
— Transfer the moist filter and the filter cake to the combustion apparatus according to manufacturer’s instructions and proceed according to 9.3.
The laboratory should ensure that the nitrate washing procedure is sufficient to remove all inorganic halides typically found in the types of samples routinely analysed. If the concentration of AOX is found to decrease with additional washing stages, then the number of nitrate washes should be increased accordingly, without increasing the volume of washing solution.
Laboratories should evaluate the methods’ repeatability for the test sample mass routinely used. Test sample masses below 25 mg often result in increased repeatability standard deviation. In case of difficult filtration properties, centrifuging the suspension before filtration is recommended.
9.3 Combustion The temperature in the combustion apparatus (7.1.1) shall be at least 950 °C; select other operating parameters in accordance with the manufacturer’s instructions. Introduce the sample into the heated zone of the combustion tube and combust according to manufacturer’s instructions.
9.4 Chlorine determination, preliminary tests and daily checks
9.4.1 General The capability of the measuring device to determine halogen concentrations (7.1.3) is to be checked over the whole working range according to manufacturer’s instructions. It is recommended to check recovery of the hydrochloric acid solution (6.3) at least once before initial check of the overall procedure. In case the same staff is carrying out analysis according to EN ISO 9562, using the same apparatus and applying the shaking method, the results of the initial check (see 188.8.131.52 of EN ISO 9562:2004) of the shaking method may be used instead of the initial check described in 184.108.40.206 of this document.
The daily check according to 220.127.116.11 is to be carried out in all cases.