SIST EN ISO 10695:2000

Water quality - Determination of selected organic nitrogen and phosphorus compounds - Gas chromatographic methods (ISO 10695:2000)

Migrated from Progress Sheet (TC Comment) (2000-07-10): CEN/TC 230N285: V.A ISO lead + see file CEN/TC 230 CORR (TA/970918) ++ SPPJ_09_Y_199804 ++ 980120: ISO/DIS 10695-1 was sent out in June 1997 in ISO for ENQ. ISO agrees to ++ wait until we carry out our PQ because their texts for FDIS will not become ++ available before May/June 1998 (TA/980120)

Wasserbeschaffenheit - Bestimmung ausgewählter organischer Stickstoff- und Phosphorverbindungen -Gaschromatographische Verfahren (ISO 10695:2000)

Qualité de l'eau - Dosage de certains composés organiques azotés et phosphorés sélectionnés - Méthodes par chromatographie en phase gazeuse (ISO 10695:2000)

La présente Norme internationale spécifie deux méthodes de dosage par chromatographie en phase gazeuse de certains composés organiques azotés et phosphorés présents dans les eaux (voir Tableau 1).Les méthodes peuvent être étendues à d'autres types de substances, sous réserve qu'elles soient validées pour chaque cas particulier.L'article 3 décrit la méthode d'extraction liquide/liquide qui est applicable aux échantillons d'eaux destinées à la consommation humaine, d'eaux souterraines, d'eaux de surface et d'eaux usées, contenant jusqu'à 0,05 g/l de matières en suspension. En présence de matières organiques, de matières en suspension et de colloïdes, les interférences sont plus nombreuses et les limites de détection peuvent donc être plus élevées.NOTE  Étant donné les très faibles concentrations habituellement présentes dans les eaux, le problème de la contamination est particulièrement important. Plus le niveau mesuré est faible, plus il faut prendre de précautions.L'article 4 décrit la méthode d'extraction liquide/solide qui est applicable aux échantillons d'eaux souterraines, d'eaux de surface et d'eaux destinées à la consommation humaine, contenant des concentrations en masse supérieures ou égales à 0,05 µg/l environ. Les interférences survenant lors de l'analyse de certains types d'eaux de surface peuvent empêcher l'application de cette méthode.Des limites de détection sont données pour information dans l'annexe A.NOTE  Pour l'application de la présente Norme internationale, il est recommandé de se conformer au guide de contrôle qualité analytique pour l'analyse de l'eau (voir ISO/TR 13530).

Kakovost vode - Določevanje izbranih organskih dušikovih in fosfornih spojin - Metoda plinske kromatografije (ISO 10695:2000)

General Information

• Status: Published
• Publication Date: 30-Nov-2000
• ICS: 13.060.70 - Examination of biological properties of water
• Technical Committee: KAV - Water quality
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2000
• Due Date: 01-Dec-2000
• Completion Date: 01-Dec-2000
• Directive: 76/464/EEC - Pollution caused by certain dangerous substances discharged into the aquatic environment of the Community
• Directive: TP128 - Pravilnik o prvih meritvah in obratovalnem monitoringu odpadnih voda
• Directive: TRRTP064 - Rules on initial measurements and operational monitoring of wastewater
• Mandate: M/BC/CEN/92/45 - Water analysis
• Ref Project: EN ISO 10695:2000 - Water quality - Determination of selected organic nitrogen and phosphorus compounds - Gas chromatographic methods (ISO 10695:2000)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 10695:2000
01-december-2000
.DNRYRVWYRGH'RORþHYDQMHL]EUDQLKRUJDQVNLKGXãLNRYLKLQIRVIRUQLKVSRMLQ
0HWRGDSOLQVNHNURPDWRJUDILMH,62
Water quality - Determination of selected organic nitrogen and phosphorus compounds -
Gas chromatographic methods (ISO 10695:2000)
Wasserbeschaffenheit - Bestimmung ausgewählter organischer Stickstoff- und
Phosphorverbindungen -Gaschromatographische Verfahren (ISO 10695:2000)
Qualité de l'eau - Dosage de certains composés organiques azotés et phosphorés
sélectionnés - Méthodes par chromatographie en phase gazeuse (ISO 10695:2000)
Ta slovenski standard je istoveten z: EN ISO 10695:2000
ICS:
13.060.70 Preiskava bioloških lastnosti Examination of biological
vode properties of water
SIST EN ISO 10695:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 10695:2000

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SIST EN ISO 10695:2000

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SIST EN ISO 10695:2000
INTERNATIONAL ISO
STANDARD 10695
First edition
2000-04-01
Water quality — Determination of selected
organic nitrogen and phosphorus
compounds — Gas chromatographic
methods
Qualité de l'eau — Dosage de certains composés organiques azotés et
phosphorés sélectionnés — Méthodes par chromatographie en phase
gazeuse
Reference number
ISO 10695:2000(E)
©
ISO 2000

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SIST EN ISO 10695:2000
ISO 10695:2000(E)
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ii © ISO 2000 – All rights reserved

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SIST EN ISO 10695:2000
ISO 10695:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Normative references .2
3 Liquid/liquid extraction .2
3.1 Principle.2
3.2 Reagents.2
3.3 Apparatus .4
3.4 Sampling and sample preparation.4
3.5 Procedure .5
4 Liquid/solid extraction .6
4.1 Principle.6
4.2 Reagents.7
4.3 Apparatus .8
4.4 Sampling.8
4.5 Procedure (for RP-C18 material).8
5 Calibration .9
5.1 General.9
5.2 Calibration using external standards .9
5.3 Calibration using an internal standard.13
6 Identification and calculation .14
6.1 Identification of individual compounds.14
6.2 Calculation.14
6.3 Summary of results .15
7 Expression of results .16
8 Test report .16
Annex A (informative) Detection limits of certain organic nitrogen and phosphorus compounds.17
Annex B (informative) Examples of gas chromatograms .18
Annex C (informative) Characteristic ions for mass spectrometry.22
Annex D (informative) Precision data for certain organic nitrogen and phosphorus compounds
(liquid/solid extraction method) .23
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SIST EN ISO 10695:2000
ISO 10695:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 10695 was prepared by Technical Committee ISO/TC 147, Water quality,
Subcommittee SC 2, Physical, chemical and biochemical methods.
Annexes A, B, C and D of this International Standard are for information only.
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SIST EN ISO 10695:2000
INTERNATIONAL STANDARD ISO 10695:2000(E)
Water quality — Determination of selected organic nitrogen and
phosphorus compounds — Gas chromatographic methods
WARNING — This International Standard makes use of flammable and toxic organic solvents and some
toxic organic and phosphorus compounds. Observe the safety regulations in effect.
1 Scope
This International Standard specifies two methods for the determination of certain organic nitrogen and phosphorus
compounds in waters by gas chromatography (see Table 1).
The methods may be extended to include additional substances, provided the methods are validated for each
individual case.
Clause 3 describes the liquid/liquid extraction method, which is applicable to samples of drinking waters, ground
waters, surface waters and waste waters containing up to 0,05 g/l of suspended solids. In the presence of organic
matter, suspended matter and colloids, interferences are more numerous and consequently the detection limits of
this method can be higher.
NOTE Because of the very low concentrations normally present in the waters, the problem of contamination is extremely
important. The lower the level measured, the more precautions have to be observed.
Clause 4 describes the liquid/solid extraction method which is applicable to samples of ground water, surface water
and drinking water containing mass concentrations of about W 0,05 μg/l. Interferences occurring with the
examination of some types of surface water can prevent the application of this method.
Detection limits are given for information in annex A.
NOTE When applying this International Standard, the guide on analytical quality control for water analysis (see
ISO/TR 13530) should be followed.
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SIST EN ISO 10695:2000
ISO 10695:2000(E)
Table 1 — Organic nitrogen and phosphorus compounds analysed by these methods
a
Name Molecular formula Molar mass
CAS No.
Atrazine C H ClN 215,7 001912-24-9
8 14 5
Cyanazine C H ClN 240,7 021725-46-2
9 13 6
Metazachlor C H ClN O 277,8 067129-08-2
14 16 3
Parathion (ethyl) C H NO PS 291,3 00056-38-2
10 14 5
Parathion (methyl) C H NO PS 263,2 298-00-0
8 10 5
C H N O
Pendimethalin 281,3 040487-42-1
13 19 3 4
C H ClN
Propazine 229,7 000139-40-2
9 16 5
C H ClN
Sebuthylazine 229,7 007286-69-3
9 16 5
Simazine C H ClN 201,7 000122-34-9
7 12 5
Terbuthylazine C H ClN 229,7 005915-41-3
9 16 5
Trifluralin C H F N O 335,3 001582-09-8
13 16 3 3 4
Vinclozolin C H Cl NO 286,1 050471-44-8
12 9 2 3
a
Chemical Abstracts Registry Number.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 5667-1:1980, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes.
ISO 5667-2:1991, Water quality — Sampling — Part 2: Guidance on sampling techniques.
ISO/TR 13530:1997, Water quality — Guide to analytical quality control for water analysis.
3 Liquid/liquid extraction
3.1 Principle
The organic nitrogen and phosphorus compounds in the water sample are extracted by liquid-liquid extraction with
dichloromethane. After concentration, the sample extracts are analysed by gas chromatography, using a nitrogen-
phosphorus detector.
3.2 Reagents
All reagents, including water, shall be of sufficient purity that they do not give rise to significant interfering peaks in
the gas chromatograms of the blanks. The purity of reagents used in the procedure shall be verified for each batch
of material by running blank determinations (3.5.6).
Reagents shall be stored in glass containers.
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SIST EN ISO 10695:2000
ISO 10695:2000(E)
NOTE 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 compounds subsequently analysed. The solvent should be considered acceptable if it does not give any
detectable interfering peaks in the chromatogram for the substance of interest.
3.2.1 Water, purified using, for example, ion exchange and carbon column adsorption.
3.2.2 Dichloromethane (CH Cl ) extraction solvent.
2 2
3.2.3 Solvents for dissolution, e.g. acetone or ethyl acetate.
3.2.4 Sodium sulfate, anhydrous
Heat Na SO powder at 500 �C � 20 �Cfor 4h � 30 min, cool to about 200 �C in a muffle furnace and then to
2 4
ambient temperature in a desiccator containing magnesium perchlorate or equivalent alternative.
3.2.5 Solutions for neutralization
a) Sodium hydroxide, aqueous solution, c(NaOH) = 1 mol/l.
b) Hydrochloric acid, aqueous solution, c(HCl) = 1 mol/l.
3.2.6 Standard stock solutions
Standard stock solutions shall be prepared by dissolving pure or, if available, certified organic nitrogen and
phosphorus compounds in acetone (3.2.3).
Unless manufacturer’s information or stability trials indicate otherwise, store the solutions at around + 4 �Cin the
dark (they can be stored at around � 18 �C, but some septa closures may harden at such a temperature with
possible losses of solvent).
For compounds listed in Table 1, the stock solutions are stable for around six months. For other compounds, the
laboratory shall check the stability of the solutions.
Prior to use, the solutions shall be brought to ambient temperature.
NOTE 1 A convenient concentration of standard stock solution is obtained by weighing accurately approximately 50,0 mg of
each determinand and dissolving it in 100 ml of acetone (3.2.3).
NOTE 2 Certified commercial standards may be used.
3.2.7 Intermediate standard solutions
Prepare intermediate standard solutions by a suitable dilution of the stock solution (3.2.6) with the solvent for
dissolution (3.2.3). A typical value is 1 mg/100 ml.
Unless manufacturer’s information or stability trials indicate otherwise, store these solutions at around + 4 �Cin the
dark.
For compounds listed in Table 1, the intermediate standard solutions are stable up to two months in acetone,
except for cyanazine and vinclozolin (one week). For other compounds, the laboratory shall check the stability of
the solutions.
3.2.8 Working standard solutions
Prepare at least five different concentrations by suitable dilutions of the intermediate standard solutions (3.2.7) with
the solvent for dissolution (3.2.3). A suitable concentration range is 1 μg to 100 μg per 100 ml.
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ISO 10695:2000(E)
Unless manufacturer’s information or stability trials indicate otherwise, store these solutions at around + 4�Cin the
dark.
The lifetime of these solutions is limited to one week for the compounds listed in Table 1. For other compounds, the
laboratory shall check the stability of the solutions.
NOTE At these low concentrations, degradation by light and adsorption onto the glass become more apparent.
3.3 Apparatus
3.3.1 Gas chromatograph, fitted with a capillary column, a nitrogen-phosphorus detector and a data processing
system.
At least two glass or fused-silica capillary columns shall be used, with an inside diameter of less than 0,4 mm and a
length of 25 m to 60 m, coated with stationary phases of different polarity allowing the separation of the compounds
of interest.
NOTE If a mass spectrometer is used for confirmation, one capillary column is normally sufficient.
Annex B provides examples of gas chromatographic conditions and the corresponding chromatograms.
3.3.2 Separating funnels, nominal capacities 1 l to 5 l, with grease-free glass or polytetrafluoroethylene (PTFE)
tap.
3.3.3 High-speed stirrer and dichloromethane-washed magnetic stirring bar, coated with PTFE.
3.3.4 Any suitable system for evaporation.
3.3.5 Microlitre syringes.
3.3.6 Miscellaneous glassware.
Laboratory glassware may be cleaned for example using a cleaning agent (laboratory detergent), followed by either
a treatment with chromium(VI)/sulfuric acid mixture, or peroxodisulfate/sulfuric acid mixture and after rinsing with
water subsequently washed with dichloromethane.
The efficacy of the treatment shall be randomly verified experimentally, using blank determinations to ensure that
no interfering contamination has occurred.
3.4 Sampling and sample preparation
Take samples in accordance with ISO 5667-1 and ISO 5667-2.
Some organic nitrogen and phosphorus compounds can degrade rapidly in an aqueous environment. Therefore,
unless stability trials indicate otherwise, extract the sample within one day of collection for phosphorus compounds
and within two days of collection for nitrogen compounds. If extraction is delayed beyond one day, the extent of the
delay shall be noted in the test report.
Collect the water samples in glass bottles cleaned as described in 3.3.6 (do not use plastics bottles) with ground-
glass stoppers or with screw caps with PTFE liners. Fill the bottles above the shoulders.
Samples shall be protected from daylight using, for example, brown glass bottles, aluminium foil, etc.
On sample collection, take care that no interfering substances enter the water sample, and no losses of the
determinands occur. This is especially important with sampling apparatus using plastics tubings.
When losses by adsorption are suspected, it shall be proved by control tests (3.5.6 and 5.2.3) that no losses by
adsorption occur.
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SIST EN ISO 10695:2000
ISO 10695:2000(E)
Glass and stainless steel devices shall preferably be used.
Measure the sample pH and, if necessary, correct the pH immediately after collection in order to be in the range
pH 6 to 9, by adding the appropriate neutralization solutions (3.2.5) (the volume of reagent added shall be
negligible to the volume of water collected).
If not done at the time of sampling, this fact shall be stated in the test report.
During transport, keep the sample at about + 4�C, avoiding contamination.
3.5 Procedure
3.5.1 General
Varying recoveries and reproducibilities can be obtained with different water types. The yields of the procedure
shall be checked (see 5.2.4) and the number of extraction steps required to obtain satisfactory yields [more than
60 % (see 5.2.4)] shall be determined by the laboratory. A minimum of three extractions is necessary. See
annex A for typical recovery rates.
NOTE The limit of detection depends on the volume of water extracted, the final volume of solvent, volume injected and
detector sensivity. Typically a sample of 500 ml and a final extract volume of 1 ml are used.
3.5.2 Sample pretreatment
Sample pretreatment is normally not necessary.
It is recommended to perform the extraction in the sampling bottle.
Where the sample bottle is completely filled, shake and pour off excess sample in order to obtain sufficient free
volume for the subsequent addition of the solvent.
Measure the volume of the water to be extracted by weighing the bottle before extraction and after emptying, or
with a volumetric cylinder.
3.5.3 Extraction in the sampling bottle and further separation
Use a sample volume of about 0,5 l to 1 l.
NOTE Some circumstances can require different volumes.
Add the dichloromethane (3.2.2) to the sample (3.5.2) (typically 50 ml of dichloromethane per 500 ml of water) and
shake for at least 10 min or use a high-speed stirrer (3.3.3).
Transfer into a separating funnel of suitable capacity (3.3.2) and allow the phases to separate.
Run the aqueous phase back into the sample container. Repeat the extraction twice with 20 ml of the solvent
(3.2.2) per 500 ml of sample.
If previous tests indicate yields less than 60 % or strong emulsions are encountered, repeat the extraction with a
new portion of the solvent.
Collect the solvent extract and dry it, using an appropriate procedure, for example:
� to the flask, add about 5 g of anhydrous sodium sulfate (3.2.4) and swirl. Leave to stand for 5 min. If the
sodium sulfate has aggregated after this period and there are no separate grains, add more sodium sulfate,
swirl and leave to stand for a further 5 min. Decant the extract into the concentration apparatus. Wash the
sodium sulfate with a further 10 ml to 20 ml of solvent (3.2.2) and add the washings to the evaporating vessel,
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SIST EN ISO 10695:2000
ISO 10695:2000(E)
or
� freeze the extract at � 18�C for 2 h. Decant the solvent extract from the ice and transfer to the evaporating
vessel. Rapidly wash the vial with a few millilitres of cooled solvent (3.2.2) and add the washings to the
evaporating vessel.
3.5.4 Concentration of the extract
Concentrate the combined dried extracts from 3.5.3 using the evaporation system (3.3.4).
Evaporate at a temperature less than 40�C, just to dryness, and add exactly 1 ml of the solvent used for the
calibration solutions.
3.5.5 Gas chromatography
Set up the gas chromatograph (3.3.1), fitted with a suitable column, according to the instructions of the
manufacturer and ensure it is in a stable condition.
Inject the extract [usually 1 μl to 10 μl, but the same volume as used for calibration (clause 5)] into the gas
chromatograph.
The requirements applicable to the extent of the measurements, and the calibration, evaluation and calculation
techniques to be used, are described in clauses 5 and 6.
Compare the gas chromatogram obtained to those of the standard solutions (see clause 5).
Evaluate the gas chromatogram qualitatively and quantitatively (see clause 6).
Check the obtained gas chromatogram for the absence of overlapping peaks occurring at the locations of the
retention times of the determinands of interest.
Chromatograms of standards should be checked for any retention time and/or peak resolution changes, losses
caused by decomposition within the chromatographic system (beware of dirty glass inserts in the injector device).
Any change in the solvent composition may affect the detector response.
3.5.6 Blank determination
Carry out the complete procedure (pretreatment, extraction, concentration, gas chromatographic analysis) using a
sample of pure water (3.2.1).
If the blank value is too high, namely greater than 10 % of the lowest measured value for any of the compounds of
interest, carry out a step-by-step examination of the procedure and eliminate the cause.
If sample concentrations are close to the limit of determination, blank values greater than 10 % of the lowest
measured value can be tolerated.
The blank value shall be subtracted only if the between-batch standard deviation of the blank value does not
significantly exceed the standard deviation of the calibration function.
4 Liquid/solid extraction
4.1 Principle
The compounds in the water sample are, if necessary after neutralization, enriched on reversed phase (RP)-C18
material or other adsorbent, eluted with a solvent and then determined by gas chromatography, using a
nitrogen-phosphorus detector.
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SIST EN ISO 10695:2000
ISO 10695:2000(E)
4.2 Reagents
All reagents, including water, shall be of sufficient purity that they do not give rise to significant interfering peaks in
the gas chromatograms of the blanks. The purity of reagents used in the procedure shall be verified for each batch
of material by running blank determinations (3.5.6).
Reagents shall be stored in glass containers.
NOTE 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 compounds subsequently analysed. The solvent should be considered acceptable if it does not give any
detectable interfering peaks in the chromatogram for the substance of interest.
4.2.1 Water, purified using, for example, ion exchange and carbon column adsorption.
4.2.2 RP-C18 material or other adsorbent.
Adsorbent may be for example in the form of commercially available cartridges or adequately filled glass columns
with a minimum packing height of 1 cm.
A higher packing height with the same packing quantity may improve the recovery. The selectivity of the material is
dealt with in 4.3.2.
4.2.3 Conditioning solvents, for example, methanol, acetone.
4.2.4 Solvent for the elution, for example, methanol, acetone.
4.2.5 Solutions for neutralization.
Identical to those used for liquid/liquid extraction. See 3.2.5.
4.2.6 Standard stock solutions.
Identical to those used for liquid/liquid extraction. See 3.2.6.
4.2.7 Intermediate standard solutions.
Prepare intermediate standard solutions by a suitable dilution of the stock solution (4.2.6) with the solvent used for
the elution (4.2.4). A typical value is 1 mg/100 ml.
Unless manufacturer’s information or stability trials indicate otherwise, store these solutions at around + 4 �Cin the
dark.
For compounds listed in Table 1, the intermediate standard solutions are stable up to two months in acetone,
except for cyanazine and vinclozolin (one week). For other compounds, the laboratory shall check the stability of
the solutions.
4.2.8 Working standards.
Prepare at least five different concentrations by suitable dilutions of the intermediate standard solutions (4.2.7) with
the solvent (3.2.3). A suitable concentration range is 1 μg/100 ml to 100 μg/100 ml.
Unless manufacturer’s information or stability trials indicate otherwise, store these solutions at around � 4 �Cin the
dark.
The lifetime of these solutions is limited to one week for compounds listed in Table 1. For other compounds, the
laboratory shall check the stability of the solutions.
NOTE At these low concentrations, degradation by light and adsorption onto the glass become more apparent.
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4.2.9 Inert gas, high purity, minimum 99,996 % (volume fraction), for drying and, if need be, for concentration by
evaporation.
4.3 Apparatus
Equipment or parts of it which may come into contact with the sample or its extract shall be free from residues
causing blanks. It is recommended to use glass, stainless steel or polytetrafluoroethylene (PTFE).
4.3.1 Gas chromatograph.
Identical to that used for liquid/liquid extraction. See 3.3.1.
4.3.2 Cartridges, made of glass or polypropylene, filled with RP-C18 material or other adsorbents.
The commercially available RP-C18 materials are often of varying quality. Considerable batch-to-batch differences
in quality and selectivity of this material may occur. Therefore for each new batch of RP-C18 material, the recovery
shall be checked according to 5.2.4. The recovery may also vary with the concentration. Calibration and analysis
shall be performed with material from one and the same batch only.
4.3.3 Vacuum pump or pressure assembly.
4.3.4 Any suitable system of evaporation.
4.3.5 Microlitre syringes.
4.3.6 Glass-fibre filter.
4.3.7 Miscellaneous glassware.
Identical to that used for liquid/liquid extraction. See 3.3.6.
4.4 Sampling
Procedure identical to that used for liquid/liquid extraction. See 3.4.
Suspended matter in the water sample (such as iron hydroxide, calcium carbonate) occurring on sampling, storage
and sample preparation can clog the packing. In this case, filter the water sample through a glass-fibre filter (4.3.6)
prior to the enrichment.
4.5 Procedure (for RP-C18 material)
4.5.1 Conditioning
Wash
...