ISO 6468:1996 pdf free download.Water quality — Determination of certain organochiorine insecticides, polychiorinated biphenyls and chlorobenzenes — Gas chromatographic method after liquid-liquid extraction.
Any substance capable of producing a response on the electron-capture detector, at a retention time indistinguishable from any compound of interest, will interfere. In practice, many potentially interfering substances wl be removed during the extraction and clean-up procedures.
NOTE I In general, the use of two capillary columns of different polarity is euWicisnt for the organocNorino compounds analysed accorcfdng to ISO 6468. The results so calculated should be considered as the maximum concentrations, possIy still influenced by coelutin9 substances. It is possible that there will be cases where a more definite Identification Is requIred.
4 Reagents and materials
All reagents shall be sufficiently pure to not give rise to significant interfering peaks in the gas chromatograms of the blanks. The purity of reagents used in the procedure shall be checked by blank determinations
(7.6).
NOTE 2 Commercial pesticide grade” solvents are available. The use of these products Is recommended only after verifying their quality. The quality of a solvent is checked by evaporation of about 200 ml down to 1 ml and analysis of the concentrate to determine the conounds subsequently analysed. The solvent should be consIdered acceptable if it does not give any detectable interfering peaks in the chro matogram br the substance of interest.
4.1 Water purified, for example, using ion-exchange or carbon-column adsorption.
4.2 Extraction solvent.
Hexane, petroleum ether or heptane are suitable.
NOTE 3 Any omer solvents meeting the requirements of
8.3 (recovery rate 60 %) may be used.
4.3 Sodium sulfate (Na?S04), anhydrous.
Heat a portion of about 250 ml to 300 ml of sodium sulfate powder at 500 °C ±20 °C for 4 h ± 30 mire, cool to about 200 C in a muffle furnace and then to ambient temperature in a desiccator containing magnesium perchlorate or an equivalent alternative,
4.4 Decane (C1oH) or dodecane (C12H), or any keeper which is not detected by the electron-capture detector.
4.5 Dry alumina.
Heat a batch of inert alumina, containing particles of size 50 m to 200 lirn and of maximum mass 500 g, at 500°C ± 20 °C for 4 h ±30 mm on a silica dish in a
The containers containing the solutions shall be marked or weighed so that any evaporation losses of the solvent may be recognized. The solutions shall be stored in volumetric flasks with ground-glass stoppers at a temperature 01 4 C in the dark. Pnor to use, they shall be brought to ambient temperature and the level of solvent shall be adjusted, if necessary.
NOTE S A convenient concenh’ation of standard stock solution Is obtaNied by weighIng 50 mg of each determinand and dissoMng It In 100 ml of the solvent.
The solution is stable for about 1 year.
4.13 Intermediate standard solutions.
Prepare intermediate standard solutions by a suitable dilution of the stock solution (4.12) with the extraction solvent (4.2).
A typical value is 10 pg/mI.
Store the intermediate standard solutions at about 4 °C in the dark. These solutions are stable for six months.
4.14 WorkIng standard solutions.
Prepare at least live different concentrations by suitable dilutions of the intermediate standard solutions (4.13) with the extraction solvent (4.2).
Suitable concentrations are in the nanograms per millilitre range.
Store the solutions at about 4°C in the dark. These solutions are stable for at least one month.
415 Cotton wool or glas. wool, washed with extraction solvent.
4.16 Water-miscible solvent.
NOTE 6 Acetone, methanol or dimethylforrnamide may be
5 Apparatus
5.1 Gas chromatograph, with an electron-capture detector (ECD) and suitable for use with capillary cdurrw s. This shall be operated in accordance with the manufacturer’s instructions. On-column or glass-lined injectIon systems can be used. The oven shall be suItable for isothermal and temperature-programmable operation.
5.2 CapIllary columns, glass or fused-silica capillaries. with an inside diameter 0f less than 0,4 mm and
6 SamplIng and sample preparation
Take samples according to ISO 5667-1 and ISO 5667-2.
Collect the water samples in brown glass bottles cleaned as described in 5.14 (do not use plastics bottles) with ground-glass stoppers or with screw caps with PTFE hners, of nominal capacity I litre to 5 litres Fill the bottles to 80 % 1o90 %.
On sample collection, ensure that no interfering substances enter the water sample, and no losses of the determinands occur. This is especially important when using plastics tubing with the sampling apparatus. If necessary. it shall be proved by control tests that no losses by adsorption occur. Glass and stainless steel devices shafl preferably be used.
Check the pH. If necessary, correct the pH immediately after collection in order to be in the range pH 5 to
7,5.
II endosulfan Is to be determined, take a separate sample and keep it under acidic conditions (pH 2) until extraction.
Do not place sanles in dose proximity to the concntrated insecticide or PCB or chlorobenzene solutions. Store In the dark at a temperature of approximately 4°C prior to extraction.
Ensure that all samples are extracted as soon as possible (preferably within 24 h) to avoid decomposItion of the compounds after sampling.
Halogenated hydrocarbons of low volatility and organochionne insecticides are relatively stable if transferred into an organic solvent, Therefore, it is permissible to store the dried solvent extracts in a refrigerator at 4 C for up to two months. Evaporation of the solveni can still occur even under refrigeration. Extracts shall not be allowed to go to dryness and the volume of solvent shall be restored to the original amount before starting analysis.
7 Procedure
7.1 Sample pretreatment
Sample pretreatment is not normally necessary.
If the sample container is filled up to the ground-glass joint, shake and pour off 30 ml to 100 ml of the sample in order to obtain sufficient free volume for the 8ub- sequent addition of the solvent.
— Freeze the extract at — 18 °C for 2 h. The solvent extract Is decanted from the ice and transferred to the evaporating vesse’. The ice is washed with a further 10 ml of solvent (4.2) and the washings are added to the evaporating vessel.
72.2 ExtractIon with a magnetic or a high-speed stirrer and separation In a microseparator
Add 20 rrd to 30 ml of the extraction solvent (4.2) to the sample (7.1).
With a magnetic stirrer and a stirring bar (5.4), stIr for at least 10 mm, at a speed of at least 1 000 r/min (the solvent needs to be dispersed finely In the water) keeping the sample covered, and then allow the phases to separate. Alternatively, if a high-speed stirrer (5.4) is used, stir for 2 mm while keeping the sample covered at a temperature of 4 °C and allow the phases to separate.
A5somblc the rnicroscpcirator (5.5); pour purified water (4.1) into the funnel until the surface of the organc phase rises sufficiently for the extract to be withdrawn with a pipette.
Dry the extract as described in 7.2.1.
7.3 ConcentratIon of the extract
Concentrate the combined dried extracts from either
721 or 72.2 by either of the procedures described in
7.3.1 or 7.3.2 or by any other suitable system (5.8).
Ensure that no significant losses of the more volatile
determinands of interest occur.
7.3.1 Concentration using a Kuderna-Danish evaporator
Good detection limits can be obtained by evaporating the sample extract to a small volume with the Kudema-Danish evaporator (5.6) and a Snyder micro- column (5.7) as follows.
Collect the dried extract in a Kudema-Danish evaporator.
Add two anti-bumping granules (4.11) and evaporate to 5 ml ± 1 ml on a steam bath. Further concentrate the extract to less than 1 nd using a Snyder microcolumn or a gentle stream of clean inert gas (e.g. nitrogen) with a tube placed In a warm water bath (not exceeding 40 °C).
NOTE 9 No further precaiAlons are necessary If the extract Is evaporated with this apparatus to a final volizne of not less than 0.5 ml. if a smaller final volume is required, it is recommended to use a keoper (4.4) In order to avoid sqllhcant losses. Decane cm’ dodecane may be used as keepers because they are not detected by the electron.