ASTM E516-95a(2005)
(Practice)Standard Practice for Testing Thermal Conductivity Detectors Used in Gas Chromatography
Standard Practice for Testing Thermal Conductivity Detectors Used in Gas Chromatography
SIGNIFICANCE AND USE
Although it is possible to observe and measure each of the several characteristics of a detector under different and unique conditions, it is the intent of this practice that a complete set of detector specifications should be obtained at the same operating conditions. It should be noted also that to specify a detector’capability completely, its performance should be measured at several sets of conditions within the useful range of the detector. The terms and tests described in this practice are sufficiently general so that they may be used at whatever conditions may be chosen for other reasons.
Linearity and speed of response of the recorder used should be such that it does not distort or otherwise interfere with the performance of the detector. Effective recorder response, Refs. (5, 6) in particular, should be sufficiently fast that it can be neglected in sensitivity of measurements. If additional amplifiers are used between the detector and the final readout device, their characteristics should also first be established.
SCOPE
1.1 This practice is intended to serve as a guide for the testing of the performance of a thermal conductivity detector (TCD) used as the detection component of a gas chromatographic system.
1.2 This practice is directly applicable to thermal conductivity detectors which employ filament (hot wire) or thermistor sensing elements.
1.3 This practice is intended to describe the performance of the detector itself independently of the chromatographic column, in terms which the analyst can use to predict overall system performance when the detector is coupled to the column and other chromatography system components.
1.4 For general gas chromatographic procedures, Practice E 260 should be followed except where specific changes are recommended herein for the use of a TCD. For definitions of gas chromatography and its various terms see Practice E 355.
1.5 For general information concerning the principles, construction, and operation of TCD see Refs. ().
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 This standard 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 safety and health practices and determine the applicability of regulatory limitations prior to use. For specific safety information, see Section 4.
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Designation: E516 − 95a (Reapproved2005)
Standard Practice for
Testing Thermal Conductivity Detectors Used in Gas
Chromatography
This standard is issued under the fixed designation E516; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This practice is intended to serve as a guide for the 2.1 ASTM Standards:
testing of the performance of a thermal conductivity detector E260Practice for Packed Column Gas Chromatography
(TCD) used as the detection component of a gas chromato- E355PracticeforGasChromatographyTermsandRelation-
graphic system. ships
1.2 This practice is directly applicable to thermal conduc- 2.2 CGA Standards:
CGAP-1SafeHandlingofCompressedGasesinContainers
tivity detectors which employ filament (hot wire) or thermistor
sensing elements. CGAG-5.4 Standard for Hydrogen Piping Systems at
Consumer Locations
1.3 This practice is intended to describe the performance of
CGAP-9 The Inert Gases: Argon, Nitrogen and Helium
the detector itself independently of the chromatographic
CGAV-7 Standard Method of Determining Cylinder Valve
column, in terms which the analyst can use to predict overall
Outlet Connections for Industrial Gas Mixtures
system performance when the detector is coupled to the
CGAP-12Safe Handling of Cryogenic Liquids
column and other chromatography system components.
HB-3 Handbook of Compressed Gases
1.4 For general gas chromatographic procedures, Practice
E260 should be followed except where specific changes are
3. Significance and Use
recommended herein for the use of a TCD. For definitions of
3.1 Although it is possible to observe and measure each of
gas chromatography and its various terms see Practice E355.
the several characteristics of a detector under different and
1.5 For general information concerning the principles,
unique conditions, it is the intent of this practice that a
construction, and operation of TCD see Refs. (1-4).
complete set of detector specifications should be obtained at
the same operating conditions. It should be noted also that to
1.6 The values stated in SI units are to be regarded as
specify a detector’s capability completely, its performance
standard. No other units of measurement are included in this
should be measured at several sets of conditions within the
standard.
useful range of the detector. The terms and tests described in
1.7 This standard does not purport to address all of the
thispracticearesufficientlygeneralsothattheymaybeusedat
safety concerns, if any, associated with its use. It is the
whatever conditions may be chosen for other reasons.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 3.2 Linearity and speed of response of the recorder used
bility of regulatory limitations prior to use. For specific safety should be such that it does not distort or otherwise interfere
with the performance of the detector. Effective recorder
information, see Section 4.
response, Refs. (5, 6) in particular, should be sufficiently fast
that it can be neglected in sensitivity of measurements. If
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.19 on Separation Science.
Current edition approved Sept. 1, 2005. Published September 2005. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
approved in 1974. Last previous edition approved in 2000 as E516–95a(2000). contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
DOI: 10.1520/E0516-95AR05. Standards volume information, refer to the standard’s Document Summary page on
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof the ASTM website.
this practice. Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
See Appendix X1. Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E516 − 95a (2005)
additional amplifiers are used between the detector and the 5.2.5.8 Method of measurement, and
final readout device, their characteristics should also first be
5.2.5.9 Type of power supply (for example, constant
established.
voltage, constant current).
5.2.5.10 For capillary detectors, the make-up gas, carrier,
4. Hazards
and reference flows should be stated.
4.1 Gas Handling Safety—Thesafehandlingofcompressed
5.3 Methods of Measurement:
gases and cryogenic liquids for use in chromatography is the
5.3.1 Sensitivitymaybemeasuredbyanyofthreemethods:
responsibility of every laboratory. The Compressed Gas
5.3.1.1 Experimental decay with exponential dilution flask
Association,(CGA),amembergroupofspecialtyandbulkgas
(8, 9) (see 5.4),
suppliers, publishes the following guidelines to assist the
5.3.1.2 Utilizing the permeation tube (10), under steady-
laboratory chemist to establish a safe work environment.
state conditions (see 5.5),
Applicable CGA publications include: CGAP-1, CGAG-5.4,
5.3.1.3 Utilizing Young’s apparatus (11), under dynamic
CGAP-9, CGAV-7, CGAP-12, and HB-3.
conditions (see 5.6).
5.3.2 Calculation of TCD sensitivity by utilizing actual
5. Sensitivity (Response)
chromatogramsisnotrecommendedbecauseinsuchacasethe
5.1 Definition:
amount of test substance corresponding to the peak cannot be
5.1.1 Sensitivity (response) of the TCD is the signal output
established with sufficient accuracy.
per unit concentration of a test substance in the carrier gas, in
5.4 Exponential Decay Method:
accordance with the following relationship (7):
5.4.1 A mixing vessel of known volume fitted with a
S 5AF /W (1)
c
magnetically driven stirrer is purged with the carrier gas at a
where: known rate. The effluent from the flask is delivered directly to
the detector. A measured quantity of the test substance is
S = sensitivity (response), mV·mL/mg,
introduced into the flask, to give an initial concentration, C ,
A = integrated peak area, mV·min,
o
F = carrier gas flow rate (corrected to detector of the test substance in the carrier gas, and a timer is started
c
temperature ), mL/min, and simultaneously.
W = mass of the test substance in the carrier gas, mg.
5.4.2 The concentration of the test substance in the carrier
gas at the outlet of the flask, at any time is given as follows:
5.1.2 If the concentration of the test substance in the carrier
gas,correspondingtoadetectorsignalisknown,thesensitivity
C 5 C exp@2F t/V # (3)
t o c f
is given by the following relationship:
where:
S 5 E/C (2)
d
C = concentrationofthetestsubstanceattime t after introduction
t
into the flask, mg/mL,
where:
C = initialconcentrationoftestcompoundintroducedinthe
o
E = peak height, mV, and
flask, mg/mL,
C = concentration of the test substance in the carrier gas at 4
d
F = carrier gas flow rate, corrected to flask temperature
c
the detector, mg/mL.
mL/min,
5.2 Test Conditions: t = time, min, and
V = volume of flask, mL.
5.2.1 Normalbutaneisthepreferredstandardtestsubstance.
f
5.2.2 The measurement must be made within the linear
5.4.3 Todeterminetheconcentrationofthetestsubstanceat
range of the detector.
the detector, C , it is necessary to apply the following
d
5.2.3 The measurement must be made at a signal level at
temperature correction:
least 100 times greater than the minimum detectability (200
C 5 C T /T (4)
~ !
d t f d
times greater than the noise level) at the same conditions.
5.2.4 The rate of drift of the detector at the same conditions
where:
must be stated.
C = concentration of the test substance at the detector,
d
5.2.5 The test substance and the conditions under which the
mg/mL,
detector sensitivity is measured must be stated. This will
T = flask temperature, K, and
f
include but not necessarily be limited to the following:
T = detector temperature, K.
d
5.2.5.1 Type of detector (for example, platinum-tungsten
5.4.4 Thesensitivityofthedetectoratanyconcentrationcan
filament type),
be calculated by:
5.2.5.2 Detector geometry (for example, flow-type,
diffusion-type),
S 5 E/C (5)
d
5.2.5.3 Internal volume of the detector,
where:
5.2.5.4 Carrier gas,
S = sensitivity, mV·mL/mg,
5.2.5.5 Carrier gas flow rate (corrected to detector
E = detector, signal, mV, and
temperature),
C = concentration of the test substance at the detector,
d
5.2.5.6 Detector temperature,
mg/mL.
5.2.5.7 Detector current,
E516 − 95a (2005)
NOTE 1—This method is subject to errors due to inaccuracies in
permitsthebandtospreadandbedetectedasaGaussianband.
measuring the flow rate and flask volume. An error of 1% in the
The detector signal is then integrated by any suitable method.
measurement of either variable will propagate to 2% over two decades in
This method has the advantage that no special equipment or
concentration and to 6% over six decades.Therefore, this method should
devices are required other than conventional chromatographic
not be used for concentration ranges of more than two decades over a
hardware. For detectors optimized for capillary column flow
single run.
NOTE 2—A temperature difference of 1°C between flask and flow
rates,uncoated,deactivated,fusedsilicatubingshouldbeused.
measuring apparatus will, if uncompensated, introduce an error of ⁄3 %
5.6.2 The sensitivity of the detector is calculated from the
into the flow rate.
peak area according to 5.1.1.
NOTE 3—Extreme care should be taken to avoid unswept volumes
betweentheflaskandthedetector,asthesewillintroduceadditionalerrors
NOTE 7—Care should be taken that the peak obtained is sufficiently
into the calculations.
widesotheaccuracyoftheintegrationisnotlimitedbytheresponsetime
NOTE 4—Flask volumes between 100 and 500 mLhave been found the
of the detector or of the recording device.
most convenient. Larger volumes should be avoided due to difficulties in
NOTE8—Peakareasobtainedbyintegration(A)orbymultiplyingpeak
i
obtaining efficient mixing and likelihood of temperature gradients.
heightbypeakwidthathalfheight(A )differby6%foraGaussianpeak:
c
5.5 Method Utilizing Permeation Tubes:
A 50.94 A (7)
c i
5.5.1 Permeation tubes consist of a volatile liquid enclosed
in a section of plastic tubing.They provide low concentrations
6. Minimum Detectability
of vapor by diffusion of the vapor through the walls of the
6.1 Definition—Minimum detectability is the concentration
tubing. The rate of diffusion for a given permeation tube is
of the test substance in the carrier gas which gives a detector
dependent only on the temperature. As the weight loss over a
signal equal to twice the noise level and is calculated from the
period of time can be easily and accurately measured
measured sensitivity and noise level values as follows:
gravimetrically, the rate of diffusion can be accurately deter-
mined. Hence, these devices have been proposed as primary
D 52N/S (8)
standards.
where:
5.5.2 Accurately known concentrations can be prepared by
D = minimum detectability, mg/mL,
passingagasoverthepreviouslycalibratedpermeationtubeat
N = noise level, mV, and
constant temperature. The concentration of the test substance
S = sensitivity of the detector, mV·mL/mg.
in the gas can then be easily calculated according to the
following relationship:
6.2 Test Conditions—Measure sensitivity in accordance
with the specifications given in Section 5. Measure noise level
C 5 R /F (6)
T c
in accordance with the specifications given in Section 9. Both
where:
measurements have to be carried out at the same conditions
C = concentration of the test substance in the gas, mg/mL,
(for example, carrier gas identity and flow rate, detector
R = permeationrateofthetestsubstanceatthetemperature
T temperature, and current) and preferably at the same time.
of the permeation tube, mg/min, and
When giving minimum detectability, state the noise level on
F = flow rate of the gas over the tube at the temperature of
c
which the calculation was based.
the tube, mL/min.
NOTE 5—If the flow rate of the gas is measured at a temperature
7. Linear Range
differentfromthetubetemperature,correctionmustbemade,asdescribed
in Appendix X1.
7.1 Definition—The linear range of a TCD is the range of
concentrations of the test substance in the carrier gas, over
5.5.3 When using a permeation tube for the testing of a
which the sensitivity of the detector is constant to within 5 %
TCD, the carrier gas is passing over a previously calibrated
as determined from the linearity plot specified in 7.2.2.
permeation tube containing the test substance at constant
7.1.1 The linear range may be expressed in three different
temperatureandintroducedimmediatelyintothedetector,kept
ways:
at the desired temperature. Knowing the concentration of the
7.1.1.1 As the ratio of the upper limit of linearity obtained
test substance in the carrier gas leaving the permeation tube at
from the linearity plot, and the minimum detectability, both
the temperature of the tube, the concentration at detector
measured for the same test substance as follows:
temperature can be calculated directly, by applying the correc-
tion specified in 5.4.2. Knowing this value and the detector
L.R. 5 ~C ! /D (9)
d
max
signal,thesensitivityofthedetectorcanbeobtainedaccording
where:
to the equation given in 5.4.4.
L.R. =
linear range of the detector,
NOTE 6—Permeation tubes are suitable only for preparing relatively
=
(C ) upperlimitoflinearityobtainedfromthelinearity
d max
low concentrations in the part-per-million range. Hence for detectors of
plot, mg/mL, and
relatively low sensitivity or of higher noise levels, this method may not
D = minimum detectability, mg/mL.
satisfy the criteria given in 5.2.3, which requires that the signal be at least
100 times greater than the noise level.
If the linear range is expressed by this ratio, the minimum
5.6 Dynamic Method: detectability must also be stated.
5.6.1 In this method a known quantity of test substance is 7.1.1.2 By giving the minimum detectability and the upper
−6
injected into the flowing carrier gas stream.Alength of empty limit of linearity (for example, from 1×10 mg/mL to
−1
tubing between the sample injection point and the detector 2×10 mg/mL).
E516 − 95a (2005)
7.1.1.3 Bygivingthelinearityplotitself,withtheminimum and lower limits. The dynamic range can be greater than the
detectability indicated on the plot. linear range, but obviously cannot be smaller.
8.1.1 Thedynamicrangemaybeexpressedinthreedifferent
7.2 Method of
...
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