《ISO-11423-1-1997.pdf》由会员分享，可在线阅读，更多相关《ISO-11423-1-1997.pdf（21页珍藏版）》请在三一文库上搜索。
1、INTERNATIONAL STANDARD IS0 11423-I First edition 1997-06-15 Water quality - Determination of benzene and some derivatives - Part I: Head-space gas chromatographic method Qualitd de kau - DBtermination du benz a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii Copyright International Organ
2、ization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 06:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11423-1:1997(E) Introduction This par-t of IS0 11423 describes a head-sp
3、ace method of sample treatment for the gas chromatographic determination of benzene and some of its derivatives in water. For an extraction procedure followed by gas chromatography, see IS0 11423-2. Which of these methods is applicable in a given case depends for instance on the type of sample to be
4、 analysed and the instruments available to the analyst. The method used is then described in the test report. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 06:10:04 MDTNo repro
5、duction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD 0 IS0 IS0 11423-l : 1997(E) Water quality - Determination of benzene and some derivatives - Part 1: Head-space gas chromatographic method 1 Scope The method described is applicable to the determination of benzene,
6、methylbenzene (toluene), dimethylbenzenes (xylenes) and ethylbenzene (abbreviated hereafter to BTX) in homogeneous samples of water and waste water in concentrations above 2 l.rg/I. In samples that are organically polluted, the limit of determination may, depending on the matrix of the sample, be hi
7、gher. High concentrations may be determined by diluting the sample. A number of further derivatives and nonpolar compounds with similar physical properties may also be determined by this method. The applicability of the method should be verified for the particular water sample. 2 Principle A defined
8、 volume of unfiltered water sample is heated in a gas-tight septum-covered vial. After establishment of equilibrium between the gaseous and liquid phases, an aliquot of the gaseous phase is transferred to a gas chromatograph. Separation of benzene and its derivatives is carried out by injection on t
9、wo capillary columns with stationary phases of different polarity (e.g. by simultaneous splitting) and determination using a suitable detector (for identification of compounds see 7.3). 3 Interferences Loss of BTX may occur during sampling, transport storage and preparation of samples due to evapora
10、tion and stripping. Volatile organic compounds in the ambient air may contaminate water samples and water used for blank tests, leading to high limits of detection and high blank values, respectively. To avoid errors due to sorption or desorption of constituents, samples should not come into contact
11、 with plastics materials. Compared with the extraction procedure in IS0 11423-2, interferences due to suspended matter or emulsifiers are less frequent with head-space analysis. Solvents can modify the normal equilibrium with the gaseous phase. The presence of a second liquid phase prohibits the use
12、 of the head-space method. Specific problems in the gas chromatographic system shall be handled according to the manufacturer s instruction, Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale,
13、04/19/2007 06:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11423-1:1997(E) IS0 The determination may be hindered by superposition of other hydrocarbons, for instance mineral oil constituents, which may also result in column overload. If the results from the two
14、 different columns differ significantly, repeat the analysis with another separating phase or a specific detector. 4 Apparatus Keep all precleaned bottles and vials in an upside-down position for 1 h at 150 “C in a ventilated drying oven before use. After this procedure, protect them from pollution,
15、 for instance by covering them with aluminium foil while they cool and closing them as soon as they are cool. 4.1 Conical-shoulder bottles, nominal capacity e.g. 250 ml, of non-actinic glass with tight stopper or PTFE- or aluminium-lined cap. 4.2 Magnetic stirrer with PTFE-coated bars. 4.3 Heating d
16、evice (e.g. water bath). 4.4 Pipettes, capacity e.g. 1 ml, 2 ml, 5 ml, 10 ml, 25 ml and 50 ml, made of glass. 4.5 Gas washing-bottle attachment with ground glass cone and sintered disc. 4.6 Graduated flasks, capacity 100 ml, 250 ml and 1 000 ml. 4.7 Crimp-top sampling vials with PTFE or aluminium-co
17、ated septum and filler cap, suited to the automatic head-space dosing system used. 4.8 Automatic head-space dosing system with thermostatting facility or heatable gas-tight injection syringe, nominal capacity 25 ml or 5 ml. The correct choice of the syringe is essential to minimize the injection err
18、or. 4.9 Crimp-top vials with PTFE septum and filler cap, capacity 10 ml, for the stock solutions. 4.10 Gas chromatograph with glass insert assembly and flame ionization detector (FID), supplied with gases as specified by the manufacturer. 4.11 Capillary columns for gas chromatography (see annex 9).
19、NOTE - If alkanes with retention times identical with BTX are expected, the Kovacs indices are useful for the choice of the columns used. 4.12 Injection syringes, capacity 50 ul and 100 yl. 5 Reagents Use only reagents of recognized analytical grade and only water complying with 5.1. Copyright Inter
20、national Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 06:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 IS0 11423-l : 1997(E) 5.1 Water for dilutions and the reag
21、ent blank. The BTX content of the water shall be as low as possible. In case of contamination, the water may be treated as follows: Fill the water into conical-shoulder bottles (4.1) place a gas washing-bottle attachment (4.5) near the bottom of the bottle, heat the water to approximately 60 “C. Pas
22、s a stream of nitrogen (approximately 180 ml/min) through the water for 1 h, then allow the water to cool to room temperature while still passing nitrogen through it. Close the bottle tightly and store in the dark. If necessary, pass nitrogen through the water immediately before use. Check the quali
23、ty of the water before and after treatment. If contamination is still detected, use another gas for purification, or purify the gas used. 5.2 Operating gases for the gas chromatographic system (nitrogen, helium, hydrogen, synthetic air) according to the manufacturer s instruction. 5.3 Calibration st
24、andard substances, each of highest purity. Benzene C6H6 Methylbenzene (toluene) C7H8 1,2-Dimethylbenzene (o-xylene) C8H10 1,3-Dimethylbenzene (m-xylene) C8H10 1,4-Dimethylbenzene (p-xylene) C8H10 Ethylbenzene C8H10 5.4 Dimethylformamide, HCON(CH if it can be turned, it can leak when heated. 7 Proced
25、ure 7.1 General At the start of the procedure the laboratory shall establish whether the conditions chosen ensure a static equilibrium. A temperature of at least 60 “C for at least 1 h has been found sufficient. The minimum time and the temperature shall be the same for samples and blank. If the pro
26、cedure is changed, repeat the check on the establishment of the equilibrium. If using an automatic sample-dosing system (4.8) follow the manufacturer s instructions for optimization. Take care to avoid contamination of the system through samples. After static equilibrium has been reached, inject an
27、aliquot of the head space into the gas chromatograph, with calibration, handling blank and air blank samples arranged at the beginning and at the end of a sampling series. If using manual sample-dosing, take an aliquot of the head space using the syringe (4.12) - heated to about 20 “C above the chos
28、en temperature -to inject into the gas chromatograph. An injection volume of not more than 1 1 is recommended. 7.2 Gas chromatography Adjust the gas chromatograph according to the manufacturer s instructions. To ensure identification of the respective compounds, use at least two capillary columns wi
29、th stationary phases of different polarity. It is advantageous to have both capillary columns mounted on one injector for simultaneous sample injection. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not
30、for Resale, 04/19/2007 06:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 IS0 11423-1:1997(E) Glass or silica columns, coated with silicone or methyl silicone separating phases cross-linked (chemically bonded) with variable phenyl content may be used (see annex 6)
31、. For detection, use a flame ionization detector (FID) with linear operating characteristics over the measuring range. It may be necessary to use a more selective detector e.g. mass spectrometer (MS), photo-ionization detector (PID) to improve compound identification. Use of two columns with station
32、ary phases of different polarity does not completely exclude peak overlap. If the results from the two columns used differ, peak overlap may be the reason; in this case the lower value is usually more accurate than the higher one. Example of gas chromatograms are given in annex C. 7.3 Blank measurem
33、ent Benzene is present ubiquitously in trace levels. For this reason, perform blank measurements using water (5.1) prior to and during a series of analyses. Blank measurements should include all steps of the analytical procedure from sampling to the evaluation of the gas chromatogram. If blank value
34、s are unusually high (more than 10 % of the lowest measured values), every step in the procedure shall be checked in order to find the reason for these high blank values. Blank values should be reduced as much as possible by various procedures such as elimination of contamination by ambient air and
35、checking of the gas chromatographic or integration parameters. If sample concentrations are close to the limit of detection, however, blank values higher than 10 % of the lowest measured value shall be tolerated. The blank value shall be deducted only if the standard deviation of the blank value doe
36、s not significantly exceed the standard deviation of the calibration function. 7.4 Identification of individual compounds Identify an individual compound by comparing its retention time in the sample with that corresponding in the calibration solutions. In order to ensure correct identification, the
37、 retention times should not differ from one another in a series of analyses by more than if using PID, within 20 %. 5 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 06:10:04 MDT
38、No reproduction or networking permitted without license from IHS -,-,- IS0 11423-1:1997(E) IS0 In low-polluted waters, or waters whose matrix is well known before the analysis, identification is very probable using one column only, and quite certain using two. The evaluation of the certainty of iden
39、tification lies with the analyst and shall be described in conjunction with the results. 8 Calibration and adjustment 8.1 General The calibration function obtained for a particular determinand is valid only for the concentration range and the sample pretreatment concerned, including the solvent used
40、 for preparing the calibration solutions. It is also dependent on the working condition of the chromatographic system, which has to be checked regularly. For routine purposes an adjustment of the calibration function using the following procedure is necessary: take two calibration solutions, one in
41、the range of 1 % to 20 % and the other at approximately 80 % of the linear working range, and analyse them twice. Determine the arithmetic mean at the two concentration levels, plot the concentration against the instrument response. Check this graph against the most recent calibration curve obtained
42、 by the full calibration procedure. If the graph falls within the confidence interval of the calibration curve, this curve may be retained, if not, perform a full calibration. Table 1 explains the subscripts that are used in the following text. Table 1 - Subscripts used in this part of IS0 11423 Sub
43、script Meaning i identity of the substance I e I value measured at calibration I I t I total method I I i consecutive number for pairs of values I 8.2 Calibration of the total method using an external standard For calibration of the total method, use aqueous solutions of the compounds to be determin
44、ed. Use dimethyl- formamide, propan-e-one or methanol (5.4) as solution aid, to ensure rapid and even distribution of the compounds in water. Choose the concentration of the solution aid so that the volume added is as small as possible (1 ml per litre of water as a maximum), so that there is no inte
45、rference with the distribution equilibrium. 8.3 Preparation of the stock solution Place into 10 ml crimp-top vials (4.9) 5 ml of dimethylformamide or other solvent (5.4) and 100 ul each of benzene and the other compounds needed. Close with the septum and shake vigorously. Prior to use, leave the sol
46、ution at room temperature for 15 min. Store the stock solutions preferably at - 20 “C in the dark; they are stable for at least a week. 8.4 Preparation of the calibration solution Fill a graduated 1 OOO-ml-flask (4.6) with water (5.1) and place it on a magnetic stirring apparatus (4.2). Open the cri
47、mp-top vial (4.7) and take an appropriate amount of stock solution (usually 50 1). Stir the water in the flask so that there is a vortex, and dose the stock solution into the water, dipping the tip of the syringe needle into the water. 6 Copyright International Organization for Standardization Provi
48、ded by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 06:10:04 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 11423-1:1997(E) Immediately after dosing the stock solution, reduce the rotational speed of the magnetic stirrer, close the flask and stir for another hour. If 50 ul of stock solution are used, the concentration of benzene in this calibration solution is 878 us/I. Using a pipette, place 5 ml of this calibration solution into a head-space vial (4.7) containing potassium car