ASTM E1140-95(2000)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E1140–95 (Reapproved 2000)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope CGAP-9 The Inert Gases: Argon, Nitrogen and Helium
CGAV-7 Standard Method of Determining Cylinder Valve
1.1 This practice is intended to serve as a guide for testing
Outlet Connections for Industrial Gas Mixtures
the performance of a nitrogen/phosphorus thermionic ioniza-
CGAP-12 Safe Handling of Cryogenic Liquids
tion detector (NPD) used as the detection component of a gas
HB-3 Handbook of Compressed Gases
chromatographic system.
1.2 This practice applies to an NPD that employs a heated
3. Terminology
alkalimetalcompoundandemitsanelectricalchargefromthat
3.1 Definitions:
solid surface.
3.1.1 For definitions of gas chromatography and its various
1.3 This practice addresses the operation and performance
terms, see Practice E355.
of the NPD independently of the chromatographic column.
3.2 Definitions of Terms Specific to This Standard:
However,theperformanceisspecifiedintermsthattheanalyst
3.2.1 drift—the average slope of the noise envelope ex-
can use to predict overall system performance when the
pressed in amps/h as measured over ⁄2h.
detector is coupled to the column and other chromatographic
3.2.2 linear range—range of mass flow rates of nitrogen or
components.
phosphorus in the carrier gas, over which the sensitivity of the
1.4 Forgeneralchromatographicprocedures,PracticeE260
detector is constant to within 5% as determined from the
should be followed except where specific changes are recom-
linearity plot.
mended herein for the use of a nitrogen/phosphorus (N/P)
3.2.3 minimum detectability—themassflowrateofnitrogen
thermionic detector.
or phosphorus in the carrier gas that gives a detector signal
1.5 This standard does not purport to address all of the
equal to twice the noise level.
safety concerns, if any, associated with its use. It is the
3.2.4 noise (short term)—the amplitude, expressed in am-
responsibility of the user of this standard to establish appro-
peres, of the baseline envelope that includes all random
priate safety and health practices and determine the applica-
variationsofthedetectorsignalofafrequencygreaterthanone
bility of regulatory limitations prior to use. For specific safety
cycle per minute.
information, see Section 5, Hazards.
3.2.5 selectivity—the ratio of the response per gram of
2. Referenced Documents nitrogenorphosphorusinthetestsubstancetotheresponseper
gram of carbon in octadecane.
2.1 ASTM Standards:
E260 Practice for Packed Column Gas Chromatography
4. Significance and Use
E355 Practice for Gas Chromatography Terms and Rela-
2 4.1 Although it is possible to observe and measure each of
tionships
the several characteristics of a detector under different and
2.2 CGA Standards:
unique conditions, it is the intent of this practice that a
CGAP-1 Safe Handling of Compressed Gases in Contain-
3 complete set of detector specifications be obtained at the same
ers
operating conditions, including geometry, flow rates, and
CGAG-5.4 Standard for Hydrogen Piping Systems at
3 temperatures. To specify a detector’s capability completely, its
Consumer Locations
performance should be measured at several sets of conditions
within the useful range of the detector. The terms and tests
This practice is under the jurisdiction ofASTM Committee E13 on Molecular described in this practice are sufficiently general so that they
Spectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-
may be used under any chosen conditions.
tography.
4.2 Linearity and speed of response of the recorder should
Current edition approved May 15, 1995. Published July 1995. Originally
be such that it does not distort or otherwise interfere with the
published as E1140–86. Last previous edition E1140–93.
Annual Book of ASTM Standards, Vol 14.02.
performanceofthedetector.Effectiverecorderresponseshould
Available from Compressed Gas Association, Inc., 1725 Jefferson Davis
Highway, Arlington, VA 22202-4100.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1140–95 (2000)
be sufficiently fast so that its effect on the sensitivity of material containing an alkali metal, often rubidium. The
measurement is negligible. If additional amplifiers are used inorganicmaterialmaybeasaltorsilicate.Itisusually,butnot
between the detector and the final readout device, their necessarily, present in bead form and may be combined with
characteristics should first be established. other components for mechanical support, such as a ceramic
core.
5. Hazards
7.3 The inorganic salt mixture is usually connected to, or
5.1 Gas Handling Safety—Thesafehandlingofcompressed supported by, a wire of platinum or other noncorrosive mate-
gases and cryogenic liquids for use in chromatography is the
rial. In some designs the bead is heated by passing a current
responsibility of every laboratory. The Compressed GasAsso- through this wire; in others, the bead is heated by hydrogen
ciation, (CGA), a member group of specialty and bulk gas
combustion, for example, the burning flame itself.
suppliers, publishes the following guidelines to assist the 7.4 The carrier gas (usually helium or nitrogen) flows
laboratory chemist to establish a safe work environment.
through a jet as in normal FID practice and mixes, prior to
Applicable CGA publications include: CGAP-1, CGAG-5.4, leaving the jet, with a small volume of hydrogen. Combustion
CGAP-9, CGAV-7, CGAP-12, and HB-3.
gas (usually air) is fed around the jet in some manner and then
moves over or around the bead before exiting from the
6. Application
detector. It is worth noting that if this mixture is lean enough,
6.1 The N/P thermionic detector is an element-specific
due to low hydrogen flow, there will be insufficient fuel to
ionization detector that is essentially a major modification of
maintain a true flame.
the flame ionization detector (FID). As in the normal FID, it
8. Equipment Preparation
measures increase in ionization current passing between two
8.1 The detector shall be evaluated as part of a gas chro-
electrodes, one of which is polarized relative to the other.
Usually these are the inorganic salt source and the collector, matograph using injections of liquid samples that have a range
of component concentrations.
with one often being at ground potential.
6.2 The mechanism of the detector will only be discussed 8.1.1 The detector shall be operated with carrier gas type
and hydrogen and oxidizer gas flow rates as recommended by
briefly in this practice partly because full understanding of the
detector is not presently available and partly because the themanufactureroftheequipment.Noattemptwillbemadein
this practice to guide the selection of optimum conditions,
substantial differences in bead chemistry, detector geometry,
except to state that because selectivity and sensitivity of the
and bead heating mechanism prevent a singular view being
NPD are very dependent on the hydrogen flow rate, several
given.
flow rates (in the range 1 to 8 mL/min for the electrically-
6.3 The addition of a heated alkali metal compound in the
detector area causes enhancement of the response for carbon- heated bead detector) should be tested for optimum detector
performance.
nitrogen and carbon-phosphorus bonds. In addition, the selec-
tivity of response can be further enhanced when the bead is 8.1.2 The complete set of performance specifications must
be determined at the same operating conditions, since the
electrically heated. Lower hydrogen and air flow rates that
diminishthenormalflameionizationresponseforhydrocarbon absolute sensitivity and noise vary independently over a wide
range depending on the operating conditions. Once selected,
compoundscanbeused.Thisselectiveenhancementallowsthe
NPD to be used for the detection of very small quantities of the operating conditions should not be changed during the
determination of the detector characteristics.
nitrogen- and phosphorus-containing compounds without in-
terference from the signal of other molecular species. 8.1.3 Detector stability over the course of the evaluation is
essential for meaningful results. This may be monitored by
6.4 TheselectiveresponsetoC-NandC-Pbondsmeansthat
the detector is not suitable for permanent gas or elemental checking the bead temperature, the heating current, gas flows,
and other parameters during the evaluation as dictated by the
nitrogen or phosphorus analysis in the true definition of the
term. It should be noted, however, that some volatile inorganic instrument manufacturer. (Some electrically-heated beads tend
tolosesensitivitycontinuouslywithoperatingtimeandrequire
phosphorous compounds do give a strong response with this
detector, comparable to that of organophosphorous com- increasing the bead heating current to recover lost sensitivity.)
8.2 Column—Any column that fully separates the sample
pounds.
components without causing overload or sample adsorption
7. Detector Construction
may be used. One suitable column isa4ftby2mm glass
7.1 There is a wide variation in the method of construction column packed with 100/120 mesh deactivated chromosorb W
of this detector. It is not considered pertinent to review all coated with 2 wt.% dimethyl silicone oil.
aspects of the different detector designs available, but to 8.3 Gases—With N/P thermionic detectors it is of critical
consider one generalized design as an example and recognize importance that all gases are pure and that the gas lines are not
that many significant variants may exist. Examples of signifi- contaminated with oils, solder flux, etc. The use of well
cant differences may exist in bead chemistry and method of conditioned molecular sieve traps in all lines helps to achieve
heating, space jet and collector configuration, potential applied this purity. If the chromatograph is fitted with in-line chemical
across the cell, its polarity, and the flow rates and composition filters after the gas regulators and flow controllers, they also
of the three gases used. should be well conditioned to ensure that no contaminants
7.2 An essential part of the N/P thermionic detector is the reach the column from elastomeric diaphragms contained in
presence, in the active area of the detector, of an inorganic these parts.
E1140–95 (2000)
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
will vary for different manufacturers’ devices but may include
8.4 Gas Connections—All gas tubing and connections
accurate constant voltage supplies or pulse-generating equip-
should be made of cleaned copper or stainless steel, including
ment.Theinstructionmanualshouldbestudiedandthoroughly
all ferrules and joints within the system. Vespel and graphite
understood before attempting to use electronic integration for
ferrulesmaybeusedforGCcolumnconnectionsprovidedthat
peak area or peak height measurements.
they are sufficiently conditioned after installation. These steps
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),
electrometer range setting.
malathion for phosphorus response (9.38% phosphorus), and
11.2 Azobenzene is the standard nitrogen-containing test
octadecane for specificity (84.95% carbon). Azobenzene and
substance. Malathion is the standard phosphorus-containing
malathion should be mixed in an appropriate ratio to allow
test substance. Measurement of the test substance must be
comparable peak heights under the isothermal conditions used.
made within the linear range of the detector and at a signal
Typical ratios are between 0.5 and 2.0, depending on detector
level at least 100 times greater than the minimum detectability
construction and operating conditions. Concentration limits
(200 times greater than noise level).
between 1 µg/L and 1 mg/L are recommended initial values.
The octadecane need be checked only at one concentration
12. Test Conditions
level for specificity, and the recommended concentration for
12.1 Measure the noise level in accordance with the speci-
this should be 1 g/L.
fications given in Section 13. Measure sensitivity in accor-
9.2 Because of the toxicity of malathion, it is recommended
dance with the specifications given in 14.1. Both sensitivity
that a dilute solution be used as the starting material, and that
and noise level measurements must be carried out under the
this solution be purchased from one of the special supply
same conditions (for example, carrier gas flow rate and
housesthatroutinelymakechemicalstandards.Precautionsfor
detector temperature) and preferably at the same time. When
handling toxic materials must be followed throughout the
stating the minimum detectability, state the noise level on
dilution sequence as standard good laboratory practice.
which the calculation was based.
9.3 Sample Injection—The recommended procedure for
accurate injection of liquid samples is the “solvent flush,” or
13. Procedure for Noise and Drift Measurement
Burke injection technique, in which a carefully washed 10 µL
13.1 Noise includes fluctuations of the baseline envelope of
syringe is loaded with 1 to 2 µLsolvent, 1 µLair, 3 µLsample,
a frequency less than one cycle per minute. The amplitude of
and 1 µL air. While time consuming, this procedure allows
these fluctuations may actually exceed the s
...