EN 14662-1:2005

SLOVENSKI STANDARD
01-september-2005
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Ambient air quality - Standard method for measurement of benzene concentrations - Part
1 : Pumped sampling followed by thermal desorption and gas chromatography
Luftbeschaffenheit - Standardverfahren zur Bestimmung von Benzolkonzentrationen -
Teil 1: Probenahme mit einer Pumpe mit anschließender Thermodesorption und
Gaschromatographie
Qualité de l'air ambiant - Méthode normalisée pour le mesurage de la concentration en
benzene - Partie 1 : Prélevement par pompage suivi d'une désorption thermique et d'une
analyse par chromatographie en phase gazeuse
Ta slovenski standard je istoveten z: EN 14662-1:2005
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 14662-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2005
ICS 13.040.20
English version
Ambient air quality - Standard method for measurement of
benzene concentrations - Part 1 : Pumped sampling followed by
thermal desorption and gas chromatography
Qualité de l'air ambiant - Méthode pour le mesurage des Luftbeschaffenheit - Standardverfahren zur Bestimmung
concentrations en benzène - Partie 1 : Echantillonage par von Benzolkonzentrationen - Teil 1: Probenahme mit einer
pompage suivi d'une désorption thermique et d'une Pumpe mit anschließender Thermodesorption und
chromatographie en phase gazeuse Gaschromatographie
This European Standard was approved by CEN on 21 March 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14662-1:2005: E
worldwide for CEN national Members.

Contents
Foreword .3
1 Scope .4
2 Normative references .4
3 Terms and definitions.4
4 Method description.5
4.1 Principle.5
4.2 Reagents and materials.6
4.3 Apparatus .8
4.4 Sample tube conditioning .9
4.5 Setting of sampling flow rate .9
4.6 Sampling.9
4.7 Procedure .10
4.8 Calculation of mass concentration of benzene .12
4.9 Report .12
5 Determination of measurement uncertainty .13
5.1 Introduction.13
5.2 Parameters contributing to measurement uncertainty .13
6 Recommendations for use .15
Annex A (informative) Extrapolated retention volumes and safe sampling volumes for benzene at
20°C.16
Annex B (informative) Description of sorbent types.17
Annex C (informative) Guidance on sorbent selection.18
Annex D (informative) Guidance on sorbent use .19
Annex E (informative) Determination of breakthrough volume from gas standards.20
Annex F (informative) Determination of breakthrough volumes from extrapolated retention volumes .22
Annex G (informative) Assessment of performance indicators and uncertainty contributions.23

Annex H (informative)  Performance characteristics.33
Bibliography.35

Foreword
This European Standard (EN 14662-1:2005) has been prepared by Technical Committee CEN/TC 264 “Air quality”,
the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical text or
by endorsement, at the latest by November 2005, and conflicting national standards shall be withdrawn at the latest
by November 2005.
This document has been prepared under a mandate given to CEN by the European Commission and the European
Free Trade Association, and supports essential requirements of EU Directive 2000/69/EC and EU Directive 96/62
EC.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
1 Scope
This part of EN 14662 gives general guidance for the sampling and analysis of benzene in air by pumped sampling,
thermal desorption and capillary gas chromatography.
This part of EN 14662 is in accordance with the generic methodology selected as the basis of the European Union
reference method for the determination of benzene in ambient air [1] for the purpose of comparison of
measurement results with limit values with a one-year reference period.

This part of EN 14662 is valid for the measurement of benzene in a concentration range of approximately 0,5 µg/m
to 50 µg/m in an air sample typically collected over a period of 24 hours.
The upper limit of the useful range is set by the sorptive capacity of the sorbent and by the linear dynamic range of
the gas chromatograph column and detector or by the sample splitting capacity of the analytical instrumentation
used. The lower limit of the useful range depends on the noise level of the detector and on blank levels of benzene
and/or interfering artefacts on the sorbent. Artefacts are typically sub ng for sorbents, but higher levels of aromatic
hydrocarbons have been noted in other sorbents. The detection limit will be approximately 1/10 of the lower
concentration range.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references,
only the edition cited applies. For undated references, the latest edition of the referenced document (including any
amendments) applies.
ENV 13005, Guide to the expression of uncertainty in measurements
EN ISO 16017-1:2000, Indoor, ambient and workplace air – Sampling and analysis of volatile organic compounds
by sorbent tube/thermal desorption/capillary gas chromatography – Part 1: Pumped sampling (ISO 16017-1:2000)
EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories (ISO/IEC
17025:1999)
3 Terms and definitions
For the purposes of this European Standard the following terms and definitions apply.
NOTE Attention is drawn to the fact that the terms Ambient Air and Limit Value are defined in Directive 96/62/EC [2].
3.1
Certified reference material
A reference material [3.5], accompanied by a certificate, one or more of whose property values are certified by a
procedure which establishes its traceability to an accurate realisation of the unit in which the property values are
expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence.
[ISO Guide 30:1992]
3.2
Combined standard uncertainty
Standard uncertainty of the result of a measurement when that result is obtained from the values of a number of
other quantities, equal to the positive square root of a sum of terms, the terms being the variances or covariances
of these other quantities weighted according to how the measurement result varies with changes in these quantities
[ENV 13005:1999]
3.3
Desorption efficiency
Ratio of the mass of analyte desorbed from a sampling device to that applied. [EN 1076:1997]
3.4
Expanded uncertainty
Quantity defining an interval about the result of a measurement that may be expected to encompass a large
fraction of the distribution of values that could reasonably be attributed to the measurand. [ENV 13005:1999]
NOTE 1 The fraction may be viewed as the coverage probability or level of confidence of the interval.
NOTE 2 To associate a specific level of confidence with the interval defined by the expanded uncertainty requires explicit of
implicit assumptions regarding the probability distribution characterised by the measurement result and its combined standard
uncertainty. The level of confidence that can be attributed to the interval can be known only to the extent to which such
assumptions may be justified.
NOTE 3 Expanded uncertainty is termed overall uncertainty in ENV 13005:1999.
3.5
Reference material
A material or substance, one or more of whose property values are sufficiently homogeneous and well established
to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to
materials.
[ISO Guide 30:1992]
3.6
Repeatability conditions
Conditions where independent test results are obtained with the same method on identical test items in the same
laboratory by the same operator using the same equipment within short intervals of time [ISO 3534-1:1993]
3.7
Sampling efficiency
Ratio of the mass of analyte collected by a sampling device to that applied
3.8
Standard uncertainty
Uncertainty of the result of a measurement expressed as a standard deviation [ENV 13005:1999]
3.9
Uncertainty (of measurement)
Parameter, associated with the results of a measurement, that characterises the dispersion of values that could
reasonably be attributed to the measurand.
NOTE 1 The parameter may be, for example, a standard deviation (or given multiple of it), or the half width of an interval
having a stated level of confidence.
NOTE 2 Uncertainty of measurement comprises, in general, many components. Some of these components may be
evaluated from the statistical distribution of the results of a series of measurements and can be characterised by experimental
standard deviations. The other components, which can also be characterised by standard deviations, are evaluated from
assumed probability distributions based on experience or other information.
NOTE 3 It is understood that the result of a measurement is the best estimate of the value of a measurand, and that all
components of uncertainty, including those arising from systematic effects, such as components associated with corrections and
reference standards, contribute to this dispersion [ENV 13005:1999].
Attention is drawn to the fact that the terms Ambient Air and Limit Value are defined in Directive 96/62/EC [2].

4 Method description
4.1 Principle
A measured volume of sample air is drawn through a sorbent tube. [EN –ISO 16017-1] Provided suitable sorbents
are chosen, benzene is retained by the sorbent and thus is removed from the flowing air stream. The collected
vapour (on each tube) is desorbed by heat and is transferred under inert carrier gas into a gas chromatograph
equipped with a capillary column and a flame ionisation detector or other suitable detector, where it is analysed.
The analysis is calibrated by means of liquid or vapour spiking onto a sorbent tube.
4.2 Reagents and materials
During the analysis, use only reagents of recognised analytical reagent grade.
Use only volumetric glassware and syringes that are calibrated to ensure traceability of volume to primary
standards.
4.2.1 Benzene
Benzene is required as a reagent for calibration purposes, using either liquid spiking (4.2.7 to 4.2.9) or vapour
spiking (4.2.4 to 4.2.6) onto sorbent tubes. The benzene used shall be of a minimum purity of 99.5%.
4.2.2 Dilution solvent
A dilution solvent is required for preparing calibration blend solution for liquid spiking (4.2.7).
NOTE Methanol is frequently used. Alternative solvents may be used provided they do not interfere with the gas chromatographic analysis,
either by co-elution or by altering detector response.
4.2.3 Sorbents
A particle size 0,18 mm to 0,25 mm (60 to 80 mesh) is recommended. Sorbent particle sizes larger than 0,18mm to
0,25 mm may be used but the breakthrough characteristics given in Annex A may be affected. Smaller sorbent
particle size ranges are not recommended because of back pressure problems. Each sorbent should be
°
preconditioned under a flow of inert gas by heating it at a temperature at least 25 C below the published maximum
for that sorbent overnight before packing the tubes. To prevent recontamination of the sorbents, they shall be kept
in a clean atmosphere during cooling to room temperature, storage, and loading into the tubes. Wherever possible,
analytical desorption temperatures should be kept below those used for conditioning. Tubes prepacked by the
manufacturer are also available for most sorbents and as such only require conditioning.
NOTE A description of sorbents is given in Annex B and a guide for sorbent selection is given in Annex C. Equivalent sorbents may be
used. A guide to sorbent conditioning and analytical desorption parameters is given in Annex D.
4.2.4 Calibration standards
Calibration standards are preferably prepared by loading the required amount benzene on the sorbent tubes from
standard atmospheres (see 4.2.5 and 4.2.6) as this procedure most closely resembles the practical sampling
situation.
NOTE The loading ranges given in 4.2.6, 4.2.7 and 4.2.9 are not mandatory and approximate to the application range given in the scope
for a 10 litre sample. For specific applications where larger volumes are used to measure lower concentrations other loading ranges may be
more appropriate.
If this way of preparation is not practicable, standards may be prepared by a liquid spiking procedure (see 4.2.7 to
4.2.9) provided that the accuracy of the spiking technique is either:
a) established by using procedures giving spiking levels fully traceable to primary standards of mass and/or volume,
or,
b) confirmed by comparison with reference materials if available, standards produced using standard atmospheres,
or results of reference measurement procedures.
To minimise matrix effects, calibration tubes should be closely matched to the sample tubes with respect to sorbent
type, particle size and mass of sorbent.
4.2.5 Standard atmospheres
Prepare standard atmospheres of known concentrations of benzene by a recognised procedure. Methods
described in ISO 6144 and ISO 6145 are suitable. If the procedure is not applied under conditions that will allow the
establishment of full traceability of the generated concentrations to primary standards of mass and/or volume the
concentrations need to be confirmed using an independent procedure.
4.2.6 Standard sorbent tubes loaded by spiking from standard atmospheres
Prepare loaded sorbent tubes by passing an accurately known volume of the standard atmosphere through the
sorbent tube e.g. by means of a pump. The volume of atmosphere sampled shall not exceed the breakthrough
volume of the sorbent. After loading the tube is disconnected and sealed. Prepare fresh standards representing
3 3
benzene levels in the samples corresponding to the concentration range of 0,5 µg/m to 50 µg/m with each batch
of samples or use spiked control samples to ensure consistency of detector response.
4.2.7 Preparation of standard solutions for liquid spiking
4.2.7.1 Solution containing approximately 100 µµµµg/ml of benzene.
Weigh a 100 ml volumetric flask and introduce approximately 75 ml of dilution solvent (4.2.2) into a 100 ml
volumetric flask. Then weigh approximately 10 mg benzene into the flask. Make up to 100 ml with dilution solvent,
stopper, weigh and shake to mix.
NOTE In order to ensure an uncertainty of the mass of benzene introduced appropriate to the application the weighing
uncertainty of the equipment used (k=2) shall be less than ± 70 µg.
4.2.7.2 Solution containing approximately 50 µµµµg/ml benzene
Introduce 30 ml of dilution solvent into a preweighed 100 ml volumetric flask. Weigh in 50 ml of solution described
in 4.2.7.1. Make up to 100 ml with dilution solvent, stopper, weigh and shake to mix.
4.2.7.3 Solution containing approximately 10 µµµµg/ml benzene
Introduce 50 ml of dilution solvent into a preweighed 100 ml volumetric flask. Weigh in 20 ml of solution described
in 4.2.7.2. Make up to 100 ml with dilution solvent, stopper, weigh and shake to mix.
4.2.7.4 Solution containing approximately 5 µµµµg/ml benzene
Introduce 50 ml of dilution solvent into a preweighed 100 ml volumetric flask. Weigh in 10 ml of solution described
in 4.2.7.2. Make up to 100 ml with dilution solvent, stopper, weigh and shake to mix.
4.2.7.5 Solution containing approximately 1 µµg/ml benzene
µµ
Introduce 50 ml of dilution solvent into a preweighed 100 ml volumetric flask. Weigh in 10 ml of solution described
in 4.2.7.3. Make up to 100 ml with dilution solvent, stopper, weigh and shake to mix.
4.2.8 Stability of standard solutions
Fresh standard solutions should be prepared weekly, or more frequently if evidence is noted of deterioration.
4.2.9 Standard sorbent tubes loaded by liquid spiking
Loaded sorbent tubes are prepared by injecting aliquots of standard solutions onto clean sorbent tubes as follows.
A sorbent tube is fitted to a T piece of which one end is fitted with a septum, or injection facility of a gas
chromatograph through which inert purge gas is passed at 100ml/min. Inject a 5µl aliquot of an appropriate
standard solution through the septum and purge for 5 minutes. The tube is then disconnected and sealed. Prepare
fresh standards with each batch of samples
NOTE 1 In the case of methanol, a purge gas flow of 100 ml/min and a 5 min purge time have been found to be appropriate to eliminate most
of the solution solvent from the tube if packed with Tenax. If other dilution solvents and sorbents are used, the conditions should be determined
experimentally.
NOTE 2 A conventional gas chromatographic injection port may be used for preparing sample tube standards. This can be used in situ, or it
can be mounted separately. The carrier gas line to the injector should be retained. The back of the injection port should be adapted if necessary
to fit the sample tube. This can be done conveniently by means of a compression coupling with an O-ring seal.

4.3 Apparatus
The following specific items of laboratory equipment are required.
4.3.1 Sorbent tubes
These tubes shall be compatible with the thermal desorption apparatus to be used (4.3.10). Typically, but not
exclusively, they are constructed of stainless steel tubing, 6,4 mm (1/4 inch) OD, 5 mm ID and 90 mm long. Tubes
of other dimensions may be used but the safe sampling volumes (SSV) given in Annex A are based on these tube
dimensions. One end of the tube is marked, for example by a scored ring about 10 mm from the sampling inlet end.
The tubes are packed with preconditioned sorbent so that the sorbent bed will be within the desorber heated zone
and a gap of at least 14 mm is retained at each end to minimise errors due to diffusive ingress at very low pump
flow rates. Tubes contain between 200 mg and 1000 mg sorbent, depending on sorbent density - typically about
250 mg porous polymer. The sorbents are retained by stainless steel gauzes and/or unsilanised glass wool plugs.
4.3.2 Sorbent tube end caps
The tubes shall be sealed, according to the requirements of EN ISO 16017-1 or equivalent. e.g. with metal screw
cap fittings with PTFE seals.
4.3.3 Syringes
A precision 10 µl liquid syringe readable to 0,1 µl. The volume of the solvent delivered shall be calibrated by
gravimetry.
4.3.4 Sampling device
Sampling device capable of maintaining a preset flow rate of 5 ml/min – 200 ml/min within ±5% during the required
sampling period (typically 24 h). As such, the following devices may be used:
• a pump with an adjustable flow rate
• a vacuum pump with a critical orifice
• a mass-flow controller operated by a vacuum pump
• a vacuum pump with a constant pressure drop over a restriction.
NOTE The sampling device should be in accordance with local safety regulations, if any.
4.3.5 Tubing
Tubing of appropriate length and internal diameter to ensure a leak-proof fit to both pump and sample tube or tube
holder, if used.
4.3.6 Flow calibration device for calibrating pump
A flow meter that is traceably calibrated to a primary flow standard over the desired flow range (4.3.5). The
uncertainty in the calibration of the flow meter shall be ≤2%.
NOTE The use of an uncalibrated integral flow meter for the calibration of pump flow rates may result in large systematic
errors.
4.3.7 Precipitation shield
A protective cover to prevent the entrance of particles or water droplets into the sampling tube during the sampling.
NOTE EN 13528-3 describes various shields for diffusive samplers that may also be suitable for pumped samplers.
4.3.8 Support
A device capable of positioning the sampling device and sorbent tube at the appropriate height and distance from
obstacles to warrant undisturbed sampling.
4.3.9 Gas chromatograph
A gas chromatograph fitted with a flame ionisation, photo ionisation detector, mass spectrometric or other suitable
detector, capable of detecting an injection of 0,5 ng benzene with a signal-to-noise ratio of at least 5 to 1.
A gas chromatograph column capable of separating benzene from other components.
4.3.10 Thermal desorption apparatus
Apparatus for the two-stage thermal desorption of the sorbent tubes and transfer of the desorbed vapour via an
inert gas flow into a gas chromatograph shall be required. A typical apparatus contains a mechanism for holding
the tubes to be desorbed whilst they are heated and purged simultaneously with inert carrier gas. The desorption
temperature and time is adjustable, as is the carrier gas flow rate. The apparatus should also incorporate additional
features, such as automatic sample tube loading, leak testing, and a cold trap in the transfer line to concentrate the
desorbed sample (4.7.2). The desorbed sample, contained in the purge gas, is routed to the gas chromatograph
and capillary column via a heated transfer line.
4.4 Sample tube conditioning
Prior to use, tubes shall be conditioned by desorbing them at a temperature at or just above the analytical
desorption temperature (see Annex D). Typical conditioning time is 10 min with a carrier gas flow of at least 100
ml/min. The carrier gas flow should be in a direction opposite to that used during sampling. Tubes should then be
analysed, using routine analytical parameters, to ensure that the thermal desorption blank is sufficiently small. If the
blank is unacceptable, tubes should be reconditioned by repeating this procedure. Once a sample has been
analysed, the tube may be reused to collect a further sample immediately. However, it is advisable to check
thermal desorption blank if the tubes are left for an extended period before reuse, or if sampling for a different
analyte is envisaged. Tubes should be sealed with metal screw caps with combined PTFE ferrule fittings and
stored in an airtight container when not sampling or being conditioned.
4.5 Setting of sampling flow rate
Calibrate the flow of the sampling device with a representative sorbent tube assembly in line, using an appropriate
external calibrated meter (4.3.4).
Determine the flow rate by taking the average of a minimum of 3 consecutive measurements. The uncertainty in the
measured flow shall be ≤ 2,5%.
The output end of the calibrated flow meter should be at atmospheric pressure to ensure proper operation.
4.6 Sampling
Select a sorbent tube appropriate for sampling benzene. Guidance on suitable sorbents is given in Annex C.
Attach the sampling device to the non marked end of the sorbent tube or tube assembly with plastic or rubber
tubing. Turn the device on and measure the flow rate and/or adjust the flow rate so that the recommended sample
volume is taken in the available time. The typical air sample volume for benzene is 10 litres.
NOTE Sampling efficiency will be 100 % (quantitative), provided the sampling capacity of the sorbents is not exceeded. If this capacity is
exceeded, breakthrough of benzene from the tube assembly will occur. The breakthrough volume may be measured by sampling from a
standard vapour atmosphere, whilst monitoring the effluent air with a flame ionisation or equivalent detector (a suitable method is described in
Annex E). Alternatively, for relatively hydrophobic sorbents, instead of determining the breakthrough volume directly, the mathematically related
retention volume may be determined. The retention volume is determined chromatographically at elevated temperatures and subsequent
extrapolation to room temperature. A suitable method is described in Annex F.
The breakthrough volume of porous polymers vary with ambient air temperature, reducing by a factor of about 2 for
°
each 10 C rise in temperature. It also varies with sampling flow rate, being reduced substantially at flow rates
below 5 ml/min or above 500 ml/min. To allow a suitable margin of safety, a safe sampling volume (SSV) is defined
such that it is a volume of not more than 70 % of the 5 %-breakthrough volume (see Annex E.1.1) or 50 % of the
retention volume (see Annex C.1). Annex A gives typical values for retention volumes and safe sampling volumes.
These values have been determined by the chromatographic method (Annex F).
NOTE 1 The safe sampling volumes in Annex A have been determined by the chromatographic method (Annex F) Measurements by the
direct method (Annex E) [3] indicate that the chromatographic method is a reliable indication of the true breakthrough capacity except under
conditions of high concentrations or very high humidity. These measurements [3] indicate that breakthrough volumes at high (80 %) humidity are
about a factor of two lower for porous polymers.
NOTE 2 Since this method uses thermal desorption, unless the TD apparatus has the facility to retrap the sample after analysis, there will
generally only be one opportunity to analyse the sample. If the sample is important and the chance of overload and/or sample breakthrough is a
possibility, a second sample at a lower flow rate should be taken.
Record the sampling period for each sample taken. Measure the flow rate again at the end of the period of
unattended operation as described in 4.4.
Knowledge of the average temperature and barometric pressure of the sampled air is required in order to express
concentrations reduced to standard conditions. This information may be obtained from measurements on the site
using a traceably calibrated thermometer and barometer. Alternatively, information from a nearby weather station
may be used.
Disconnect the sample tube assembly and seal both ends of each tube with compression seals. Tighten these
seals securely. The tubes should be uniquely labelled. Solvent containing paints and markers or adhesive labels
should not be used to label the tubes.
If samples are not to be analysed within 8 hours, they should be stored in such a way that contamination cannot
occur.
Field blanks should be prepared by using tubes identical to those used for sampling and subjecting them to the
same handling procedure as the sample tubes except for the actual period of sampling. Label these as blanks.
4.7 Procedure
4.7.1 Safety precautions
This part of EN 14662 does not purport to address all of the safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate health and safety practices and determine the
applicability of regulatory limitations prior to use.
4.7.2 Desorption and analysis
The sorbent tube is placed in a compatible thermal desorption apparatus and a leak test performed. Air is purged
from the tube to avoid chromatographic artefacts arising from the thermal oxidation of the sorbent or gas
chromatographic stationary phase. The tube is then heated to displace the organic vapours which are passed to
the gas chromatograph by means of a carrier gas stream. The gas flow at this stage should be the reverse of that
used during sampling, i.e. the marked end of the tube should be nearest the gas chromatograph column inlet. The
gas flow through the tube should be typically 30ml/min to 50 ml/min for optimum desorption efficiency.
NOTE 1 For the air purge described above it is usually necessary to use 10 x the tube volume (i.e. 20 ml to 30 ml) of inert gas to completely
displace the volume of air (2 ml to 3 ml) in the tube. However, if strongly hydrophilic sorbents are used, it may be necessary to employ a larger
purge volume to reduce sorbed air and water to prevent ice formation blocking the cold trap. During the purge period care should be taken to
minimise heating of the tube.
The desorbed sample occupies a volume of several millilitres of gas, so that pre-concentration is essential prior to
capillary GC analysis. This may be achieved using a small, cooled, secondary sorbent trap which can be desorbed
sufficiently rapidly at low flow rates (< 5 ml/min) to minimise band broadening and produce capillary compatible
peaks. Alternatively an empty secondary trap, or one containing an inert material such as glass beads, may be
used to pre-concentrate the sample, but such traps typically require cooling to below -100°C.
NOTE 2 If sub-zero capillary cryofocusing temperatures are used to preconcentrate the analytes, water should be eliminated from the
sample tube prior to desorption in order to prevent ice formation blocking the capillary tubing and stopping the thermal desorption process.
NOTE 3 If a secondary trap is not available and optimum sample tube desorption flows of 30 ml/min to 50 ml/min are used, a minimum split
ratio of 30:1 to 50:1 will typically be required for operation with high resolution capillary columns. Single stage thermal desorption may thus limit
sensitivity.
Desorption conditions should be chosen such that desorption from the sample tube is complete, and no sample
loss occurs in the secondary trap, if used. Typical parameters are:
° °
Desorption temp    180 C -325 C
Desorption time  5 min -15 min

Desorption flow rate 30 ml/min -50 ml/min
°
Secondary trap low    +20 C to -180 °C, depending on type of cold trap
° °
Secondary trap high     150 C to 350 C
Secondary trap sorbent   typically same as tubes, 25 mg to 100 mg, if used
Carrier gas  helium 99.9995 % minimum
Split ratios Split ratios between the sample tube and secondary trap and between the secondary
trap and analytical column (if applicable) should be selected dependent on expected
atmospheric concentration. (See guidance from respective manufacturers of the thermal
desorption apparatus.)
Set the sample flow path temperature (transfer line temperature) high enough to prevent analyte condensation but
not so high as to cause degradation.
Set up the gas chromatograph for the analysis of benzene. A variety of chromatographic columns may be used for
the analysis. The choice will depend largely on which compounds, if any, are present that might interfere in the
chromatographic analysis. Typical examples are 50 m x 0,22 mm fused silica columns with thick-film
(1 µm to 5 µm), poly(dimethylsiloxane) or a 50 m 7 % poly(cyanopropyl-), 7 % poly(phenyl-), 86 %
poly(methylsiloxane) stationary phase.
The capillary column or, preferably, a length of uncoated, deactivated fused silica, should be threaded back through
the transfer line from the thermal desorption apparatus to the gas chromatograph such that it reaches as close as
possible to the sorbent in the cold trap or as near as possible to the tube in a single stage desorber. Internal tubing
shall be inert and dead volumes shall be minimised. A split valve(s) is conveniently placed at the inlet and/or outlet
of the secondary trap. The split valve on the outlet of the secondary trap may be located either at the inlet or the
outlet of the transfer line. Split ratios depend on the application.
Correspondence of retention time on a single column shall not be regarded as proof of identity.
4.7.3 Calibration
Analyse each sorbent tube standard (4.2.7) by thermal desorption and gas chromatography.
A full calibration using each standard should be performed at the start of the analysis and the calibration curve
generated. A single point calibration should be performed at every tenth sample in the batch and at the end of the
batch. If the drift in these single point calibration standards is ≥ ± 5% of value then a full calibration should be
undertaken.
Prepare a calibration function from the responses of the calibration standards of benzene and the corresponding
masses of benzene in the sorbent tube standards. Various functions, such as linear, exponential or polynomial,
may be more or less suitable, depending on the linearity of the detector response. Application of weighted
regression may be necessary to obtain an appropriate goodness of fit of the function over the entire concentration
range.
The goodness of fit of the calibration function shall be determined by examining the residuals calculated for each
calibration standard concentration level as the difference between the mass of benzene calculated by application of
the calibration function and the actual mass of benzene in the standard. The requirements given in Clause 5.2 shall
be fulfilled.
The calibration shall be repeated at regular intervals. These intervals may vary in practice and will depend on the
response drift of the detector used. The calibration interval is to be established based on practical determinations of
the detector response drift. The response drift between calibrations shall be < ± 5%.
4.7.4 Determination of sample concentration
Analyse the samples and sample blanks as described for the calibration standards in section (4.7.2). Determine
the peak area and read from the calibration graph the mass of the analyte in the desorbed sample.
4.7.5 Determination of desorption efficiency
For the analysis of benzene by thermal desorption conditions may usually be set such that a desorption efficiency
of 100% is obtained. The efficiency of desorption may be checked by comparing the chromatographic response of
a sorbent tube standard (4.7.3) with that obtained by injecting aliquots of the standard solutions or the atmosphere
directly into the gas chromatograph. Thus prepare a second calibration graph of peak area against mass of analyte
as in (4.7.3), but using solutions (4.7) or (4.4). This calibration should be the same or nearly the same as that in
(4.7.3). The desorption efficiency is the response of a tube standard divided by that of the corresponding liquid
standard injected directly. If the desorption efficiency is less than 98 %, change the desorption parameters
accordingly.
4.8 Calculation of mass concentration of benzene
Calculate the concentration of benzene in the sampled air, in µg/m , by means of the following equation:
m
sam
C =     (1)
m
V
sam
where:
C = concentration of benzene in the air sampled, in µg/m
m
m = mass of benzene present in the actual sample as found in 4.7.4, in ng
sam
V = volume of sample taken, in litres.
sam
For application of the measurement result within the frame of EU Directive 2000/69/EC [1], conversion of the
concentration value to conditions of standard temperature and pressure (STP, 20 °C, 101,3 kPa) is required. The
method for conversion will depend on the type of sampling device used (mass-flow controlled or volume-flow
controlled). Equations for conversion for both cases are given in Annex G, Equations (B5) and (B9).
4.9 Report
The test report shall contain at least the following information:
a) complete identification of the sample
b) reference to this part of EN 14662
c) sampling location, sampling time period and volume of air pumped
d) barometric pressure and temperature
e) test result
f) any unusual features noted during the determination.
5 Determination of measurement uncertainty
5.1 Introduction
The measurement of the concentration of benzene in ambient air has to fulfil the requirement of a maximum
uncertainty in the measured values prescribed by Directive 2000/69/EC. In order to fulfil this requirement, the
measurement uncertainty has to be assessed by methods described in ENV 13005, ISO 5725 or equivalent
documents. In practice, input data for uncertainty assessment may be obtained from different experimental sources,
e.g. validation studies (comprising laboratory tests, field tests and/or inter-laboratory comparisons) or QA/QC
procedures (including replicate measurements of blank and control samples and certified reference materials, and
calibration procedures).
In this Standard the uncertainty assessment is based on results from laboratory tests that are used to determine
performance characteristics of the method used. The uncertainty evaluation is based on Equation (1) that - in
general terms - describes the measurement problem under consideration.
This information is supplemented by results from experiments that were performed in support of the validation of
the Standard Method.
This approach is not meant to exclude evaluations based on data from ongoing QA/QC procedures, field studies or
inter-laboratory comparisons as long as these evaluations are consistent with ENV 13005 and/or ISO 5725.
5.2 Parameters contributing to measurement uncertainty
5.2.1 Parameters to be assessed and minimum requirements
Based on Eq. (1) the parameters given in Table 1 have been identified to contribute to the uncertainty of benzene
concentrations measured by pumped sampling and subsequent sample analysis by solvent desorption and gas
chromatography.
For each of these parameters minimum requirements are given; these serve as the basis for the establishment of
ongoing QA/QC programmes: when uncertainties based on these minimum requirements are calculated, combined
and expanded according to the rules given in Annex B, the uncertainties of the measured concentrations will fulfil
the uncertainty requirement of Directive 2000/69/EC.
Table 1 - Uncertainty parameters and minimum requirements
Uncertainty parameter Symbol Section Minimum requirement
Sampled volume V G.2
Sample volume ≥ 5 litres
sam
• Sample flow – calibration and φ G.2.1 Relative uncertainty ≤ ± 2,5 %
measurement
G.2.1 Relative difference between flow before and
• Sample flow – variation during ∆φ
sampling after sampling ≤ ± 5 %
t G.2.2
• Sampling time Relative uncertainty ≤ ± 0,1%
G.2.3
• Conversion to standard Relative uncertainty ≤ ± 4%
temperature and pressure
Desorption efficiency D G.3
≥ 98 % at the limit value with a relative
uncertainty of ≤± 3%
Mass of benzene sampled m G.4
sam
• Sampling efficiency E G.4.1 ≥ 99%
A G.4.3 No significant difference between results of
• Analyte stability
analysis of samples before and after storage
G.4.4
Mass of benzene measured m
meas
m G.4.4.1
• Mass of benzene in calibration Relative uncertainty ≤ ± 2%
CS
standards
F G.4.4.2
• Lack-of-fit of calibration Relative residuals over the calibration range ≤±
function
3%; at the limit value ≤±2%
d G.4.4.3
• Response drift between ≤± 5%
calibrations
G.3
• Analytical repeatability w ≤ ± 3%
anal
• Selectivity R G.4.4.4 Resolution factor ≥ 1
Mass of benzene in sample blank m G.5
bl ≤ 2 ng with an uncertainty of ≤ ± 1 ng
Between-laboratory uncertainty 5.2.2

5.2.2 Between-laboratory uncertainty
The procedures described in Clause 4 are not restrictive but allow variations in approaches between laboratories.
In a limited series of inter-laboratory compariso
...