ASTM E594-96
(Practice)Standard Practice for Testing Flame Ionization Detectors Used in Gas or Supercritical Fluid Chromatography
Standard Practice for Testing Flame Ionization Detectors Used in Gas or Supercritical Fluid Chromatography
SCOPE
1.1 This practice serves as a guide for the testing of the performance of a flame ionization detector (FID) used as the detection component of a gas or supercritical fluid (SF) chromatographic system.
1.2 This recommended practice is directly applicable to an FID that employs a hydrogen-air or hydrogen-oxygen flame burner and a d-c biased electrode system.
1.3 This recommended practice covers the performance of the detector itself, independently of the chromatographic column, the column-to-detector interface (if any), and other system components, in terms that the analyst can use to predict overall system performance when the detector is made part of a complete chromatographic system.
1.4 For general gas chromatographic procedures, Practice E260 should be followed except where specific changes are recommended herein for the use of an FID. For definitions of gas chromatography and its various terms see Recommended Practice E355.
1.5 For general information concerning the principles, construction, and operation of an FID, see Refs (1,2 3,4 ).
1.6 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 5.
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Designation: E 594 – 96
Standard Practice for
Testing Flame Ionization Detectors Used
in Gas or Supercritical Fluid Chromatography
This standard is issued under the fixed designation E 594; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope CGA P-1 Safe Handling of Compressed Gases in Contain-
ers
1.1 This practice serves as a guide for the testing of the
CGA G-5.4 Standard for Hydrogen Piping Systems at
performance of a flame ionization detector (FID) used as the
Consumer Locations
detection component of a gas or supercritical fluid (SF)
CGA P-9 The Inert Gases: Argon, Nitrogen and Helium
chromatographic system.
CGA V-7 Standard Method of Determining Cylinder Valve
1.2 This recommended practice is directly applicable to an
Outlet Connections for Industrial Gas Mixtures
FID that employs a hydrogen-air or hydrogen-oxygen flame
CGA P-12 Safe Handling of Cryogenic Liquids
burner and a d-c biased electrode system.
HB-3 Handbook of Compressed Gases
1.3 This recommended practice covers the performance of
the detector itself, independently of the chromatographic col-
3. Terminology
umn, the column-to-detector interface (if any), and other
3.1 Definitions:
system components, in terms that the analyst can use to predict
3.1.1 drift—the average slope of the baseline envelope
overall system performance when the detector is made part of
expressed in amperes per hour as measured over ⁄2 h.
a complete chromatographic system.
3.1.2 noise (short-term)—the amplitude expressed in am-
1.4 For general gas chromatographic procedures, Practice
peres of the baseline envelope that includes all random
E 260 should be followed except where specific changes are
variations of the detector signal of a frequency on the order of
recommended herein for the use of an FID. For definitions of
1 or more cycles per minute (see Fig. 1).
gas chromatography and its various terms see Recommended
3.1.2.1 Discussion— Short-term noise corresponds to the
Practice E 355.
observed noise only. The actual noise of the system may be
1.5 For general information concerning the principles, con-
2 larger or smaller than the observed value, depending upon the
struction, and operation of an FID, see Refs (1, 2, 3, 4).
method of data collection or signal monitoring from the
1.6 This standard does not purport to address all of the
detector, since observed noise is a function of the frequency,
safety concerns, if any, associated with its use. It is the
speed of response, and the bandwidth of the electronic circuit
responsibility of the user of this standard to establish appro-
measuring the detector signal.
priate safety and health practices and determine the applica-
3.1.3 other noise—Fluctuations of the baseline envelope of
bility of regulatory limitations prior to use. For specific safety
a frequency less than 1 cycle per minute can occur in
information, see Section 5.
chromatographic systems.
2. Referenced Documents 3.1.4 Discussion—The amplitude of these fluctuations may
actually exceed the short-term noise. Such fluctuations are
2.1 ASTM Standards:
difficult to characterize and are not typically to be expected.
E 260 Practice for Packed Column Gas Chromatography
They are usually caused by other chromatographic components
E 355 Practice for Gas Chromatography Terms and Rela-
such as the column, system contaminants, and flow variations.
tionships
These other noise contributions are not derived from the
E 1449 Standard Guide for Supercritical Fluid Chromatog-
detector itself and are difficult to quantitate in a general
raphy Terms and Relationships
manner. It is, however, important for the practicing chromatog-
2.2 CGA Standards:
rapher to be aware of the occurrence of this type of noise
contribution.
This recommended practice is under the jurisdiction of ASTM Committee E13
4. Significance and Use
on Molecular Spectroscopy and is the direct responsibility of Subcommittee E13.19
on Chromatography.
4.1 Although it is possible to observe and measure each of
Current edition approved April 10, 1996. Published June 1996. Originally
published as E 594 – 77. The last previous edition E 594 – 95.
The boldface numbers in parentheses refer to the list of references appended to
this recommended practice. Available from Compressed Gas Association, Inc., 1725 Jefferson Davis
Annual Book of ASTM Standards, Vol 14.01. Highway, Arlington, VA 22202-4100.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 594
FIG. 1 Example of the FID Noise Level and Drift Measurement.
the several characteristics of a detector under different and control to near mid-scale on the recorder. Allow at least ⁄2 hof
unique conditions, it is the intent of this recommended practice baseline to be recorded. Draw two parallel lines to form an
that a complete set of detector specifications should be ob- envelope that encloses the random excursions of a frequency of
tained at the same operating conditions, including geometry, approximately 1 cycle per minute or more. Measure the
flow rates, and temperatures. It should be noted that to specify distance between the parallel lines at any particular time.
a detector’s capability completely, its performance should be Express the value as amperes of noise.
measured at several sets of conditions within the useful range 6.1.2 Measure the net change in amperes of the lower line of
of the detector. The terms and tests described in this recom- the envelope over ⁄2 h and multiply by two. Express as
mended practice are sufficiently general so that they may be amperes per hour drift.
used at whatever conditions may be chosen for other reasons.
NOTE 1—This method covers most cases of baseline drift. Occasion-
4.2 The FID is generally only used with non-ionizable
ally, with sinusoidal baseline oscillations of lower frequency, a longer
supercritical fluids as the mobile phase. Therefore, this stan-
measurement time should be used. This time must then be stated and the
dard does not include the use of modifiers in the supercritical drift value normalized to 1 h.
fluid.
6.1.3 In specifications giving the measured noise and drift
4.3 Linearity and speed of response of the recording system
of the FID, specify the test conditions in accordance with 7.2.4.
or other data acquisition device used should be such that it does
not distort or otherwise interfere with the performance of the
7. Sensitivity (Response)
detector. Effective recorder response, Refs. (5,6) in particular,
7.1 Sensitivity (response) of the FID is the signal output per
should be sufficiently fast so that it can be neglected in
unit mass of a test substance in the carrier gas, in accordance
sensitivity of measurements. If additional amplifiers are used
with the following relationship:
between the detector and the final readout device, their
A
i
characteristics should also first be established.
S 5 (1)
m
5. Hazards
where:
5.1 Gas Handling Safety—The safe handling of com-
S = sensitivity (response), A·s/g,
pressed gases and cryogenic liquids for use in chromatography
A = integrated peak area, A·s, and
i
is the responsibility of every laboratory. The Compressed Gas m = mass of the test substance in the carrier gas, g.
Association, (CGA), a member group of specialty and bulk gas
7.2 Test Conditions:
suppliers, publishes the following guidelines to assist the 7.2.1 Normal butane is the preferred standard test substance.
laboratory chemist to establish a safe work environment.
7.2.2 The measurement must be made within the linear
Applicable CGA publications include CGA P-1, CGA G-5.4, range of the detector.
CGA P-9, CGA V-7, CGA P-12, and HB-3.
7.2.3 The measurement must be made at a signal level at
least 200 times greater than the noise level.
6. Noise and Drift
7.2.4 The test substance and the conditions under which the
6.1 Methods of Measurement: detector sensitivity is measured must be stated. This will
6.1.1 With the attenuator set at maximum sensitivity (mini- include, but not necessarily be limited to, the following:
mum attenuation), adjust the detector output with the “zero”’ 7.2.4.1 Type of detector,
E 594
7.2.4.2 Detector geometry (for example, electrode to which measuring the flow rate and flask volume. An error of 1 % in the
measurement of either variable will propagate to 2 % over two decades in
bias is applied),
concentration and to 6 % over six decades. Therefore, this method should
7.2.4.3 Carrier gas,
not be used for concentration ranges of more than two decades over a
7.2.4.4 Carrier gas flow rate (corrected to detector tempera-
single run.
ture and fluid presssure),
NOTE 3—A temperature difference of 1 C between flask and flow-
7.2.4.5 Make-up gas,
measuring apparatus will, if uncompensated, introduce an error of ⁄3 %
7.2.4.6 Make-up gas flow rate,
into the flow rate.
NOTE 4—Extreme care should be taken to avoid unswept volumes
7.2.4.7 Detector temperature,
between the flask and the detector, as these will introduce additional errors
7.2.4.8 Detector polarizing voltage,
into the calculations.
7.2.4.9 Hydrogen flow rate,
NOTE 5—Flask volumes between 100 and 500 mL have been found the
7.2.4.10 Air or oxygen flow rate,
most convenient. Larger volumes should be avoided due to difficulties in
7.2.4.11 Method of measurement, and
obtaining efficient mixing and likelihood of temperature gradients.
7.2.4.12 Electrometer range setting.
NOTE 6—This method may not be used with supercritical-fluid mobile
7.3 Methods of Measurement: phases unless the flask is specifically designed and rated for the pressure
in use.
7.3.1 Sensitivity may be measured by any of three methods:
7.3.1.1 Experimental decay with exponential dilution flask
7.5 Method Utilizing Permeation Devices:
(7) (see 7.4).
7.5.1 Permeation devices consist of a volatile liquid en-
7.3.1.2 Utilizing the permeation device (8) under steady-
closed in a container with a permeable wall. They provide low
state conditions (see 7.5).
concentrations of vapor by diffusion of the vapor through the
7.3.1.3 Utilizing Young’s apparatus (9) under dynamic con-
permeable surface. The rate of diffusion for a given permeation
ditions (see 7.6).
device is dependent only on the temperature. The weight loss
7.3.2 Calculation of FID sensitivity by utilizing actual
over a period of time is carefully and accurately determined;
chromatograms is not preferred because in such a case the
thus, these devices have been proposed as primary standards.
amount of test substance at the detector may not be the same as
7.5.2 Accurately known permeation rates can be prepared
that introduced.
by passing a gas over the previously calibrated permeation
7.4 Exponential Dilution Method:
device at constant temperature. Knowing this permeation rate,
7.4.1 Purge a mixing vessel of known volume fitted with a
R , the sensitivity of the detector can be obtained from the
t
magnetically driven stirrer with the carrier gas at a known rate.
following equation:
The effluent from the flask is delivered directly to the detector.
60E
S 5
Introduce a measured quantity of the test substance into the
R
t
flask to give an initial concentration, C , of the test substance
o (4)
in the carrier gas, and simultaneously start a timer.
where:
7.4.2 Calculate the concentration of the test substance in the
S = sensitivity, A·s/g,
carrier gas at the outlet of the flask at any time as follows (see
E = detector signal, A, and
Annex A1):
R = permeation rate of a test substance from the perme-
t
C 5 C exp @2F t/V # (2)
f o f f
ation device, g/min.
where:
NOTE 7—Permeation devices are suitable only for preparing relatively
C = concentration of the test substance at time t after low concentrations in the part-per-million range. In addition, only a
f
limited range of linearity can be explored because it is experimentally
introduction into the flask, g/mL,
difficult to vary the permeation rate over an extended range. Thus, for
C = initial concentration of the test compound introduced
o
detectors of relatively low sensitivity or of higher noise levels, this method
into the flask, g/mL,
may not satisfy the criteria given in 4.2.3, which requires that the signal
F = carrier gas flow rate, corrected to flask temperature
f
be at least 200 times greater than the noise level. A further limitation in the
(see Annex A1), mL/min,
use of permeation devices is the relatively slow equilibration of the
t = time, min, and
permeation rate, coupled with the life expectancy of a typical device
V = volume of flask, mL.
f
which is on the order of a few months.
7.4.3 Calculate the sensitivity of the detector at any concen-
NOTE 8—This method may not be used with supercritical-fluid mobile
tration as follows: phase. SC-CO would adversly affect the permeation tube by either
extracting the polymer or swelling the tube, resulting in a potential safety
60E
hazard.
S 5 (3)
C F
f f
7.6 Dynamic Method:
where:
7.6.1 In this method, inject a known quantity of test sub-
S = sensitivity, A·s/g,
stance into the flowing carrier gas stream. A length of empty
E = detector signal, A,
tubing or an empty high-pressure cell between the sample
C = concentration of the test substance at time, t, after
f
injection point and the detector permits the band to spread and
introducton into the flask, g/mL, and
be detected as a Gaussian band. Then integrate the detector
F = carrier gas flow rate, corrected to flask temperature
f
signal by any suitable method. This method has the advantage
(see Annex A1), mL/min.
that no special equipment or devices are required other than
NOTE 2—This method is subject to errors due to inaccuracies in conventional chromatographic hardware.
E 594
7.6.2 As an alternative to 7.6.1, an actual chromatogram 9. Linear Range
may be generated by substituting a column for the length of
9.1 The linear range of an FID is the range of mass flow
empty tubing. This approach is not preferred because it is
rates of the test substance in the carrier gas, over which the
common for the sample to have adverse interaction with the
sensitivity of the detector is constant to within 5 % as
column. These problems can be minimized by using an inert
determined from the linearity plot specified in 9.2.2.
stable liquid phase loaded sufficiently to overcome support
9.1.1 The linear range may be expressed in three different
adsorption effects. Likewise a nonpolar sample will minimize
ways:
these adverse interactions. For example, a column prepared
9.1.1.1 As the ra
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