ASTM E1140-95(2010)e1
(Practice)Standard Practice for Testing Nitrogen/Phosphorus Thermionic Ionization Detectors for Use In Gas Chromatography
Standard Practice for Testing Nitrogen/Phosphorus Thermionic Ionization Detectors for Use 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 be obtained at the same operating conditions, including geometry, flow rates, and temperatures. To specify a detector's 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 under any chosen conditions.
Linearity and speed of response of the recorder should be such that it does not distort or otherwise interfere with the performance of the detector. Effective recorder response should be sufficiently fast so that its effect on the sensitivity of measurement is negligible. If additional amplifiers are used between the detector and the final readout device, their characteristics should first be established.
SCOPE
1.1 This practice covers testing the performance of a nitrogen/phosphorus thermionic ionization detector (NPD) used as the detection component of a gas chromatographic system.
1.2 This practice applies to an NPD that employs a heated alkali metal compound and emits an electrical charge from that solid surface.
1.3 This practice addresses the operation and performance of the NPD independently of the chromatographic column. However, the performance is specified in terms that the analyst can use to predict overall system performance when the detector is coupled to the column and other chromatographic components.
1.4 For general chromatographic procedures, Practice E260 should be followed except where specific changes are recommended in this practice for the use of a nitrogen/phosphorus (N/P) thermionic detector.
1.5 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, Hazards.
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Designation: E1140 − 95 (Reapproved 2010)
Standard Practice for
Testing Nitrogen/Phosphorus Thermionic Ionization
Detectors for Use In Gas Chromatography
This standard is issued under the fixed designation E1140; 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.
ε NOTE—Editorial corrections were made to Footnote 3 in November 2010.
1. Scope 2.2 CGA Standards:
CGAP-1SafeHandlingofCompressedGasesinContainers
1.1 This practice covers testing the performance of a
CGAG-5.4 Standard for Hydrogen Piping Systems at
nitrogen/phosphorus thermionic ionization detector (NPD)
Consumer Locations
used as the detection component of a gas chromatographic
CGAP-9 The Inert Gases: Argon, Nitrogen and Helium
system.
CGAV-7Standard Method of Determining Cylinder Valve
1.2 This practice applies to an NPD that employs a heated
Outlet Connections for Industrial Gas Mixtures
alkalimetalcompoundandemitsanelectricalchargefromthat
CGAP-12Safe Handling of Cryogenic Liquids
solid surface.
HB-3Handbook of Compressed Gases
1.3 This practice addresses the operation and performance
3. Terminology
of the NPD independently of the chromatographic column.
However,theperformanceisspecifiedintermsthattheanalyst
3.1 Definitions:
can use to predict overall system performance when the
3.1.1 For definitions of gas chromatography and its various
detector is coupled to the column and other chromatographic
terms, see Practice E355.
components.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 drift—the average slope of the noise envelope ex-
1.4 For general chromatographic procedures, Practice E260
pressed in amps/h as measured over ⁄2 h.
should be followed except where specific changes are recom-
mended in this practice for the use of a nitrogen/phosphorus
3.2.2 linear range—range of mass flow rates of nitrogen or
(N/P) thermionic detector.
phosphorus in the carrier gas, over which the sensitivity of the
detector is constant to within 5% as determined from the
1.5 This standard does not purport to address all of the
linearity plot.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2.3 minimum detectability—themassflowrateofnitrogen
priate safety and health practices and determine the applica-
or phosphorus in the carrier gas that gives a detector signal
bility of regulatory limitations prior to use. For specific safety
equal to twice the noise level.
information, see Section 5, Hazards.
3.2.4 noise (short term)—the amplitude, expressed in
amperes, of the baseline envelope that includes all random
2. Referenced Documents
variationsofthedetectorsignalofafrequencygreaterthanone
2.1 ASTM Standards:
cycle per minute.
E260Practice for Packed Column Gas Chromatography
3.2.5 selectivity—the ratio of the response per gram of
E355PracticeforGasChromatographyTermsandRelation-
nitrogenorphosphorusinthetestsubstancetotheresponseper
ships
gram of carbon in octadecane.
This practice is under the jurisdiction ofASTM Committee E13 on Molecular 4. Significance and Use
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
4.1 Although it is possible to observe and measure each of
mittee E13.19 on Separation Science.
Current edition approved Nov. 1, 2010. Published December 2010. Originally the several characteristics of a detector under different and
approved in 1986. Last previous edition approved in 2005 as E1140–95(2005).
unique conditions, it is the intent of this practice that a
DOI: 10.1520/E1140-95R10E01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
the ASTM website. 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
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E1140 − 95 (2010)
complete set of detector specifications be obtained at the same 7. Detector Construction
operating conditions, including geometry, flow rates, and
7.1 There is a wide variation in the method of construction
temperatures. To specify a detector’s capability completely, its
of this detector. It is not considered pertinent to review all
performance should be measured at several sets of conditions
aspects of the different detector designs available, but to
within the useful range of the detector. The terms and tests
consider one generalized design as an example and recognize
described in this practice are sufficiently general so that they
that many significant variants may exist. Examples of signifi-
may be used under any chosen conditions.
cant differences may exist in bead chemistry and method of
heating, space jet and collector configuration, potential applied
4.2 Linearity and speed of response of the recorder should
across the cell, its polarity, and the flow rates and composition
be such that it does not distort or otherwise interfere with the
of the three gases used.
performanceofthedetector.Effectiverecorderresponseshould
be sufficiently fast so that its effect on the sensitivity of 7.2 An essential part of the N/P thermionic detector is the
measurement is negligible. If additional amplifiers are used presence, in the active area of the detector, of an inorganic
between the detector and the final readout device, their material containing an alkali metal, often rubidium. The
characteristics should first be established. inorganicmaterialmaybeasaltorsilicate.Itisusually,butnot
necessarily, present in bead form and may be combined with
other components for mechanical support, such as a ceramic
5. Hazards
core.
5.1 Gas Handling Safety—The safe handling of compressed
7.3 The inorganic salt mixture is usually connected to, or
gases and cryogenic liquids for use in chromatography is the
supported by, a wire of platinum or other noncorrosive mate-
responsibility of every laboratory. The Compressed GasAsso-
rial. In some designs the bead is heated by passing a current
ciation (CGA), a member group of specialty and bulk gas
through this wire; in others, the bead is heated by hydrogen
suppliers, publishes the following guidelines to assist the
combustion, for example, the burning flame itself.
laboratory chemist to establish a safe work environment.
Applicable CGA publications include: CGAP-1, CGAG-5.4, 7.4 The carrier gas (usually helium or nitrogen) flows
CGAP-9, CGAV-7, CGAP-12, and HB-3. through a jet as in normal FID practice and mixes, prior to
leaving the jet, with a small volume of hydrogen. Combustion
gas (usually air) is fed around the jet in some manner and then
6. Application
moves over or around the bead before exiting from the
6.1 The N/P thermionic detector is an element-specific
detector. It is worth noting that if this mixture is lean enough,
ionization detector that is essentially a major modification of
due to low hydrogen flow, there will be insufficient fuel to
the flame ionization detector (FID). As in the normal FID, it
maintain a true flame.
measures increase in ionization current passing between two
electrodes, one of which is polarized relative to the other.
8. Equipment Preparation
Usually these are the inorganic salt source and the collector,
8.1 The detector shall be evaluated as part of a gas chro-
with one often being at ground potential.
matograph using injections of liquid samples that have a range
6.2 The mechanism of the detector will only be discussed
of component concentrations.
briefly in this practice partly because full understanding of the
8.1.1 The detector shall be operated with carrier gas type
detector is not presently available and partly because the
and hydrogen and oxidizer gas flow rates as recommended by
substantial differences in bead chemistry, detector geometry,
themanufactureroftheequipment.Noattemptwillbemadein
and bead heating mechanism prevent a singular view being
this practice to guide the selection of optimum conditions,
given.
except to state that because selectivity and sensitivity of the
NPD are very dependent on the hydrogen flow rate, several
6.3 The addition of a heated alkali metal compound in the
flow rates (in the range of 1 to 8 mL/min for the electrically
detector area causes enhancement of the response for carbon-
heated bead detector) should be tested for optimum detector
nitrogen and carbon-phosphorus bonds. In addition, the selec-
performance.
tivity of response can be further enhanced when the bead is
8.1.2 The complete set of performance specifications must
electrically heated. Lower hydrogen and air flow rates that
be determined at the same operating conditions, since the
diminishthenormalflameionizationresponseforhydrocarbon
absolute sensitivity and noise vary independently over a wide
compoundscanbeused.Thisselectiveenhancementallowsthe
range depending on the operating conditions. Once selected,
NPD to be used for the detection of very small quantities of
the operating conditions should not be changed during the
nitrogen- and phosphorus-containing compounds without in-
determination of the detector characteristics.
terference from the signal of other molecular species.
8.1.3 Detector stability over the course of the evaluation is
6.4 TheselectiveresponsetoC-NandC-Pbondsmeansthat
essential for meaningful results. This may be monitored by
the detector is not suitable for permanent gas or elemental checking the bead temperature, the heating current, gas flows,
nitrogen or phosphorus analysis in the true definition of the
and other parameters during the evaluation as dictated by the
term. It should be noted, however, that some volatile inorganic instrument manufacturer. (Some electrically-heated beads tend
phosphorous compounds do give a strong response with this tolosesensitivitycontinuouslywithoperatingtimeandrequire
detector, comparable to that of organophosphorus compounds. increasing the bead heating current to recover lost sensitivity.)
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E1140 − 95 (2010)
8.2 Column—Any column that fully separates the sample recorders/integrators/computers. The preferred system will in-
components without causing overload or sample adsorption corporate one of the newer integrators or computers that
may be used. One suitable column isa4ftby2mm glass converts an electrical signal into clearly defined peak area
column packed with 100/120 mesh deactivated chromosorb W counts in units such as microvolt-seconds.These data can then
coated with 2 wt.% dimethyl silicone oil. be readily used to calculate the linear range.
10.1.1 Another method uses peak height measurements.
8.3 Gases—With N/P thermionic detectors it is of critical
This method yields data that are very dependent on column
importance that all gases are pure and that the gas lines are not
performance and therefore not recommended.
contaminated with oils, solder flux, etc. The use of well
10.1.2 Regardless of which method is used to calculate
conditioned molecular sieve traps in all lines helps to achieve
linear range, peak height is the only acceptable method for
this purity. If the chromatograph is fitted with in-line chemical
determining minimum detectability.
filters after the gas regulators and flow controllers, they also
should be well conditioned to ensure that no contaminants
10.2 Calibration—It is essential to calibrate the measuring
reach the column from elastomeric diaphragms contained in
system to ensure that the nominal specifications are acceptable
these parts. andparticularlytoverifytherangeoverwhichtheoutputofthe
device,whetherpeakareaorpeakheight,islinearwithrespect
NOTE 1—To condition a molecular sieve 5Acolumn well, heat the trap
to input signal. Failure to perform this calibration may intro-
with a slow flow of carrier gas at 350°C for a minimum of 2 h.
duce substantial errors into the results. Methods for calibration
8.4 Gas Connections—All gas tubing and connections
will vary for different manufacturers’ devices but may include
should be made of cleaned copper or stainless steel, including
accurate constant voltage supplies or pulse-generating equip-
all ferrules and joints within the system. Vespel and graphite
ment.Theinstructionmanualshouldbestudiedandthoroughly
ferrulesmaybeusedforGCcolumnconnectionsprovidedthat
understood before attempting to use electronic integration for
they are sufficiently conditioned after installation. These steps
peak area or peak height measurements.
will minimize contamination problems.
11. Test Substances
9. Sample Preparation
11.1 The test substance and the conditions under which the
9.1 A solution containing three compounds dissolved in
detector sensitivity is measured must be stated. This will
isooctane should be used, with great emphasis placed on the
include,butnotnecessarilybelimitedto,thefollowing:typeof
purity of all chemicals and particularly the solvent. Blank runs
detector, detector geometry (for example, source of alkali
should be made on the solvent to ensure that no interfering
metal), carrier gas, carrier gas flow rate (corrected to detector
peaks elute at the same time as the compounds of interest,
temperature),detectortemperature,detectorpolarizingvoltage,
which would invalidate the results. The three test compounds
hydrogen flow rate, air flow rate, method of measurement, and
are azobenzene for nitrogen response (15.38% nitrogen),
malathion for phosphorus response (9.38% phosphorus), and electrometer range setting.
octadecane for specificity (84.95% carbon). Azobenzene and
11.2 Azobenzene is the standard nitrogen-containing test
malathion should be mixed in an appropriate ratio to allow
substance. Malathion is the standard phosphorus-containing
comparablepeakheightsundertheisothermalconditionsused.
test substance. Measurement of the test substance must be
Typical ratios are between 0.5 and 2.0, depending on detector
made within the linear range of the detector and at a signal
construction and operating conditions. Concentration limits
level at least 100 times greater than the minimum detectability
between 1 µg/L and 1 mg/L are recommended initial values.
(200 times greater than noise level).
The octadecane need be checked only at one concentration
level for specificity, and the recommended concentration for 12. Test Conditions
this should be 1 g/L.
12.1 Measure the noise level in accordance with the speci-
9.2 Because of the toxicity of malathion, it is recommended fications given in Sect
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