ASTM E1140-95(2017)
(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
4.1 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.
4.2 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific safety information, see Section 5, Hazards.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1140 − 95 (Reapproved 2017)
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.
1. Scope 2. Referenced Documents
1.1 This practice covers testing the performance of a
2.1 ASTM Standards:
nitrogen/phosphorus thermionic ionization detector (NPD)
E260Practice for Packed Column Gas Chromatography
used as the detection component of a gas chromatographic
E355PracticeforGasChromatographyTermsand Relation-
system.
ships
1.2 This practice applies to an NPD that employs a heated
2.2 CGA Standards:
alkalimetalcompoundandemitsanelectricalchargefromthat
CGAP-1SafeHandlingofCompressedGasesinContainers
solid surface.
CGAG-5.4Standard for Hydrogen Piping Systems at Con-
sumer Locations
1.3 This practice addresses the operation and performance
CGAP-9The Inert Gases: Argon, Nitrogen and Helium
of the NPD independently of the chromatographic column.
CGAV-7Standard Method of Determining Cylinder Valve
However,theperformanceisspecifiedintermsthattheanalyst
Outlet Connections for Industrial Gas Mixtures
can use to predict overall system performance when the
CGAP-12Safe Handling of Cryogenic Liquids
detector is coupled to the column and other chromatographic
HB-3Handbook of Compressed Gases
components.
1.4 For general chromatographic procedures, Practice E260
3. Terminology
should be followed except where specific changes are recom-
3.1 Definitions:
mended in this practice for the use of a nitrogen/phosphorus
(N/P) thermionic detector.
3.1.1 For definitions of gas chromatography and its various
terms, see Practice E355.
1.5 This standard does not purport to address all of the
3.2 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.2.1 drift—the average slope of the noise envelope ex-
priate safety, health, and environmental practices and deter-
pressed in amps/h as measured over ⁄2 h.
mine the applicability of regulatory limitations prior to use.
3.2.2 linear range—range of mass flow rates of nitrogen or
For specific safety information, see Section 5, Hazards.
phosphorus in the carrier gas, over which the sensitivity of the
1.6 This international standard was developed in accor-
detector is constant to within 5% as determined from the
dance with internationally recognized principles on standard-
linearity plot.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- 3.2.3 minimum detectability—themassflowrateofnitrogen
mendations issued by the World Trade Organization Technical or phosphorus in the carrier gas that gives a detector signal
Barriers to Trade (TBT) Committee. equal to twice the noise level.
1 2
This practice is under the jurisdiction ofASTM Committee E13 on Molecular For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Spectroscopy and Separation Science and is the direct responsibility of Subcom- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
mittee E13.19 on Separation Science. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2017. Published October 2017. Originally the ASTM website.
ɛ1 3
approved in 1986. Last previous edition approved in 2010 as E1140–95(2010) . Available from Compressed Gas Association (CGA), 14501 George Carter
DOI: 10.1520/E1140-95R17. Way, Suite 103, Chantilly, VA 20151, http://www.cganet.com.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1140 − 95 (2017)
3.2.4 noise (short term)—the amplitude, expressed in compoundscanbeused.Thisselectiveenhancementallowsthe
amperes, of the baseline envelope that includes all random NPD to be used for the detection of very small quantities of
variationsofthedetectorsignalofafrequencygreaterthanone nitrogen- and phosphorus-containing compounds without in-
cycle per minute. terference from the signal of other molecular species.
3.2.5 selectivity—the ratio of the response per gram of
6.4 TheselectiveresponsetoC-NandC-Pbondsmeansthat
nitrogenorphosphorusinthetestsubstancetotheresponseper
the detector is not suitable for permanent gas or elemental
gram of carbon in octadecane.
nitrogen or phosphorus analysis in the true definition of the
term. It should be noted, however, that some volatile inorganic
4. Significance and Use
phosphorous compounds do give a strong response with this
detector, comparable to that of organophosphorus compounds.
4.1 Although it is possible to observe and measure each of
the several characteristics of a detector under different and
7. Detector Construction
unique conditions, it is the intent of this practice that a
complete set of detector specifications be obtained at the same
7.1 There is a wide variation in the method of construction
operating conditions, including geometry, flow rates, and
of this detector. It is not considered pertinent to review all
temperatures. To specify a detector’s capability completely, its
aspects of the different detector designs available, but to
performance should be measured at several sets of conditions
consider one generalized design as an example and recognize
within the useful range of the detector. The terms and tests
that many significant variants may exist. Examples of signifi-
described in this practice are sufficiently general so that they
cant differences may exist in bead chemistry and method of
may be used under any chosen conditions.
heating, space jet and collector configuration, potential applied
across the cell, its polarity, and the flow rates and composition
4.2 Linearity and speed of response of the recorder should
of the three gases used.
be such that it does not distort or otherwise interfere with the
performanceofthedetector.Effectiverecorderresponseshould
7.2 An essential part of the N/P thermionic detector is the
be sufficiently fast so that its effect on the sensitivity of
presence, in the active area of the detector, of an inorganic
measurement is negligible. If additional amplifiers are used
material containing an alkali metal, often rubidium. The
between the detector and the final readout device, their
inorganicmaterialmaybeasaltorsilicate.Itisusually,butnot
characteristics should first be established.
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.
7.4 The carrier gas (usually helium or nitrogen) flows
Applicable CGA publications include: CGAP-1, CGAG-5.4,
through a jet as in normal FID practice and mixes, prior to
CGAP-9, CGAV-7, CGAP-12, and HB-3.
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
6.3 The addition of a heated alkali metal compound in the NPD are very dependent on the hydrogen flow rate, several
detector area causes enhancement of the response for carbon- flow rates (in the range of 1 to 8 mL/min for the electrically
nitrogen and carbon-phosphorus bonds. In addition, the selec- heated bead detector) should be tested for optimum detector
tivity of response can be further enhanced when the bead is performance.
electrically heated. Lower hydrogen and air flow rates that 8.1.2 The complete set of performance specifications must
diminishthenormalflameionizationresponseforhydrocarbon be determined at the same operating conditions, since the
E1140 − 95 (2017)
absolute sensitivity and noise vary independently over a wide handling toxic materials must be followed throughout the
range depending on the operating conditions. Once selected, dilution sequence as standard good laboratory practice.
the operating conditions should not be changed during the
9.3 Sample Injection—The recommended procedure for ac-
determination of the detector characteristics.
curate injection of liquid samples is the “solvent flush,” or
8.1.3 Detector stability over the course of the evaluation is
Burke injection technique, in which a carefully washed 10-µL
essential for meaningful results. This may be monitored by
syringe is loaded with 1 to 2 µLsolvent, 1 µLair, 3 µLsample,
checking the bead temperature, the heating current, gas flows,
and 1 µL air. While time consuming, this procedure allows
and other parameters during the evaluation as dictated by the
repeatability of 62% or better, and minimizes needle volume
instrument manufacturer. (Some electrically-heated beads tend
effects.
tolosesensitivitycontinuouslywithoperatingtimeandrequire
increasing the bead heating current to recover lost sensitivity.)
10. Data Handling
8.2 Column—Any column that fully separates the sample
10.1 All manufacturers supply an integral electrometer to
components without causing overload or sample adsorption allow the small electrical current changes to be coupled to
may be used. One suitable column isa4ftby2mm glass recorders/integrators/computers. The preferred system will in-
column packed with 100/120 mesh deactivated chromosorb W corporate one of the newer integrators or computers that
coated with 2 wt.% dimethyl silicone oil. converts an electrical signal into clearly defined peak area
counts in units such as microvolt-seconds.These data can then
8.3 Gases—With N/P thermionic detectors it is of critical
be readily used to calculate the linear range.
importance that all gases are pure and that the gas lines are not
10.1.1 Another method uses peak height measurements.
contaminated with oils, solder flux, etc. The use of well
This method yields data that are very dependent on column
conditioned molecular sieve traps in all lines helps to achieve
performance and therefore not recommended.
this purity. If the chromatograph is fitted with in-line chemical
10.1.2 Regardless of which method is used to calculate
filters after the gas regulators and flow controllers, they also
linear range, peak height is the only acceptable method for
should be well conditioned to ensure that no contaminants
determining minimum detectability.
reach the column from elastomeric diaphragms contained in
10.2 Calibration—It is essential to calibrate the measuring
these parts.
system to ensure that the nominal specifications are acceptable
NOTE 1—To condition a molecular sieve 5Acolumn well, heat the trap
andparticularlytoverifytherangeoverwhichtheoutputofthe
with a slow flow of carrier gas at 350°C for a minimum of 2 h.
device,whetherpeakareaorpeakheight,islinearwithrespect
8.4 Gas Connections—All gas tubing and connections
to input signal. Failure to perform this calibration may intro-
should be made of cleaned copper or stainless steel, including
duce substantial errors into the results. Methods for calibration
all ferrules and joints within the system. Vespel and graphite
will vary for different manufacturers’ devices but may include
ferrulesmaybeusedforGCcolumnconnectionsprovidedthat
accurate constant voltage supplies or pulse-generating equip-
they are sufficiently conditioned after installation. These steps
ment.Theinstructionmanualshouldbestudiedandthoroughly
will minimize contamination problems.
understood before attempting to use electronic integration for
peak area or peak height measurements.
9. Sample Preparation
11. Test Substances
9.1 A solution containing three compounds dissolved in
11.1 The test substance and the conditions under which the
isooctane should be used, with great emphasis placed on the
detector sensitivity is measured must be stated. This will
purity of all chemicals and particularly the solvent. Blank runs
include,butnotnecessarilybelimitedto,thefollowing:typeof
should be made on the solvent to ensure that no interfering
detector, detector geometry (for example, source of alkali
peaks elute at the same time as the compounds of interest,
metal), carrier gas, carrier gas flow rate (corrected to detector
which would invalidate the results. The three test compounds
temperature),detectortemperature,detectorpolarizingvoltage,
are azobenzene for nitrogen response (15.38% nitrogen),
hydrogen flow rate, air flow rate, method of measurement, and
malathion for phosphorus response (9
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.