ASTM E1511-93(2010)
(Practice)Standard Practice for Testing Conductivity Detectors Used in Liquid and Ion Chromatography
Standard Practice for Testing Conductivity Detectors Used in Liquid and Ion Chromatography
SIGNIFICANCE AND USE
This practice is intended to describe the performance of a conductivity detector independent of the chromatographic system in terms that the analyst can use to predict overall system performance when the detector is coupled to the column and other chromatography system components.
Although it is possible to observe 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, including the setup used for testing, flow rates, and temperatures. It should be noted that 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 at whatever conditions may be chosen for other reasons.
SCOPE
1.1 This practice covers the testing of the performance of conductivity detectors used as the detection component of a liquid or ion chromatography system.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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Designation: E1511 − 93 (Reapproved 2010)
Standard Practice for
Testing Conductivity Detectors Used in Liquid and Ion
Chromatography
This standard is issued under the fixed designation E1511; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.3 conductivity—since the conductance is dependent on
both the conductive properties of the solution and on the
1.1 This practice covers the testing of the performance of
dimensions of the electrodes and the cell, the conductivity (κ)
conductivity detectors used as the detection component of a
of the solution is defined to be independent of electrode and
liquid or ion chromatography system.
cell dimensions. Specifically,
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
κ 5 G (1)
A
standard.
where:
2. Referenced Documents
1 = the distance between two planer disk electrodes, and
2.1 ASTM Standards: A = the electrode’s surface area.
E1151 Practice for Ion Chromatography Terms and Rela-
3.2.3.1 Discussion—In liquid and ion chromatography, cell
tionships
dimensions are commonly measured in centimetres, so the
units of κ are S/cm. (Alternatively, the SI units of S/m may be
3. Terminology
used. S/m = 100 S/cm.)
3.1 See Practice E1151.
3.2.4 drift—the average slope of the noise envelope ex-
3.2 Definitions:
pressed in nano siemens per centimetre per hour as measured
3.2.1 cell constant—the cell constant (K) of a conductivity
over a period of 1 h.
cell is equal to 1/A,so κ =GK.
3.2.5 equivalent conductivity—of an ionic solute, the con-
3.2.1.1 Discussion—If the cell constant of the flow-through
tribution of the solute to the total conductivity of the solution,
cell used is equal to one, then the conductivity equals the
measured in microsiemens per centimetre, divided by its
conductance. Although the cell constant is often specified for
concentration in milliequivalents/litre.
conductivity detectors, there is little practical value in knowing
the constant as long as the detector is properly calibrated for 3.2.6 flow dependence rate—the change in measured con-
conductivity.
ductivity as a function of flow rate.
3.2.2 conductance—the conductance (G) of a solution is the
3.2.7 limitingequivalentconductivity—ofanionicsolute,its
inverse of the resistance measured between two electrodes in a
equivalent conductivity extrapolated to infinite dilution.
cell, expressed in units of siemens (S), equal to inverse ohms.
3.2.8 linear range—of a conductivity detector for a given
3.2.2.1 Discussion—The term resistance refers specifically
solute in a specific solvent, the concentration range of solute
to the dc resistance to ionic current, independent of the
for which the detector response factor is within 5 % of the
capacitive reactance at the interfaces between the electrodes
response factor in the middle of the range as determined from
and the solution.
the linearity plot specified in Section 11.
3.2.8.1 Discussion—The lower limit may be limited by
noise, and the upper limit by deviation from linearity. (The
This practice is under the jurisdiction of ASTM Committee E13 on Molecular
upper limit may instead be limited by the maximum full-scale
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.19 on Separation Science. deflection on the detector’s least sensitive output range.)
Current edition approved Nov. 1, 2010. Published November 2010. Originally
3.2.9 long-term noise—the maximum amplitude in nano
approved in 1993. Last previous edition approved in 2005 as E1511 - 93(2005).
DOI: 10.1520/E1511-93R10.
siemenspercentimetreforallrandomvariationsofthedetector
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
output of frequencies between 2 and 60 cycles per hour.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.9.1 Discussion—Long-term noise represents noise that
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. can be mistaken for eluting peaks.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1511 − 93 (2010)
3.2.10 minimum detectability—of a conductivity detector, 4.1.3 Dependence of response on flow rate is measured by
that concentration of solute in a specific solvent that corre- pumping 1 mM KCl through the conductivity cell at several
sponds to twice the short-term noise. flow rates and measuring the detector output.
4.1.4 Response time is measured by measuring the time
3.2.10.1 Discussion—Because of the difficulty of pumping
required for the detector output to change from that measured
solvents through the chromatographic system without any
with DI water to that measured with 1 mM KCl.
contamination of the solvents from the system, this quantity
can only be measured with solutes retained by a column. Since
5. Significance and Use
minimum detectability is dependent on the chromatographic
system used, it is not measured in this practice. However, if the
5.1 This practice is intended to describe the performance of
minimum detectability of a solute is measured on one system
a conductivity detector independent of the chromatographic
with one detector, the minimum detectability can be predicted
system in terms that the analyst can use to predict overall
when other detectors are tested on the same system by
system performance when the detector is coupled to the
comparing the measured values of short-term noise.
column and other chromatography system components.
3.2.11 response factor—of a conductivity detector, the mea-
5.2 Although it is possible to observe each of the several
sured conductivity response of a solute divided by the solute
characteristics of a detector under different and unique
concentration.
conditions, it is the intent of this practice that a complete set of
detector specifications should be obtained at the same operat-
3.2.12 response time of the detector—the time required for
ing conditions, including the setup used for testing, flow rates,
theoutputofthedetectortochangefrom10to90 %ofthenew
andtemperatures.Itshouldbenotedthattospecifyadetector’s
equilibrium value when the composition of the eluent is
capability completely, its performance should be measured at
changed in a stepwise manner, within the linear range of the
several sets of conditions within the useful range of the
detector.
detector. The terms and tests described in this practice are
3.2.12.1 Discussion—Aslow response time has the effect of
sufficiently general so that they may be used at whatever
limiting resolution for efficient peaks such as early eluting
conditions may be chosen for other reasons.
peaks and those from highly efficient columns or microbore
columns. Response time is generally dependent on three
6. Reagents
factors: (a) cell volume, (b) volume of heat transfer tubing
6.1 Reagent chemicals are reagent grade or better.
leading to the cell, and (c) electronic filtering of the output.
6.1.1 Deionized Water, (DI water), 18 M-ohm.
3.2.13 sensitivity—the detector response divided by
6.1.2 Potassium Chloride, (KCl) dry powder.
concentration, which is also the response factor (11.1.1).
6.1.3 Hydrochloric Acid, (HCl) standard 0.1000 N solution.
3.2.13.1 Discussion—Sensitivity is therefore by definition
the same for all properly calibrated conductivity detectors.
7. Preparation of Standards
(Sensitivity is often confused with minimum detectability,
7.1 Potassium Chloride Standards:
which is dependent on both sensitivity and noise.) Therefore,
7.1.1 Prepare a 10-mM KCl standard stock solution. Weigh
the calibration of the detector should be measured, and if
out 0.7455 g KCl (desiccated) and dissolve it in 18 M-ohm DI
necessary, adjusted. Follow the manufacturer’s procedure for
water in a 1-Lplastic volumetric flask. Fill the flask to 1 Lwith
calibrating the detector. The procedure in Section 9 is used by
DI water.
many manufacturers and is useful for the tests in this practice.
7.1.2 Prepare KCl standards from the 10-mM KCl standard
3.2.14 short-term noise—the maximum amplitude in nano
stock solution. Using accurate Class A pipettes, pipette the
siemenspercentimetreforallrandomvariationsofthedetector
volumes of the 10-mM standard stock solution listed below
output of a frequency greater than one cycle per minute.
into 100-mL plastic volumetric flasks. For the 1-mM KCl
3.2.14.1 Discussion—Short-term noise determines the standard,filla100-mLplasticvolumetricflaskwiththe10-mM
smallest signal detectable by a conductivity detector, limits the KCl solution and transfer to a 1-Lplastic volumetric flask. Fill
to the line with DI water.
precision available for the determination of trace samples, and
may set the lower limit of linearity.
KCl Concentration, Volume in 100 mL DI Water,
mm mL
4. Summary of Practice
0.05 0.5
0.1 1
4.1 Four different tests are performed to characterize a
0.2 2
detector.
0.5 5
1 100 mL in 1 L
4.1.1 Noise and drift are measured while a solution is
flowing through the detector cell. The test is performed using
10 mM No dilution
two different solutions: deionized water (DI) and 1 mM
potassium chloride (KCl).
7.2 Hydrochloric Acid Standards:
4.1.2 Linear range is determined by preparing a plot of 7.2.1 Prepare a 2.00-mM HCl standard stock solution by
response factor versus the log of solute concentration using diluting 20.0 mL of standard 0.1000 N HCl into a 1-L plastic
standard solutions of KCl and hydrochloric acid (HCl) as volumetric flask and filling to the line with DI water. If
solutes. standard 0.1000 N HCl is not available, a 0.10-mM HCl
E1511 − 93 (2010)
solution can be prepared by diluting 8.3 mL of 12 N (37 %) ing the detector output or, on some detectors, the output is
concentration HCl into 1 L of DI water. (The concentration of monitored on the front panel readout.
this solution will be less accurate than that prepared from
9. Calibration
0.1000 N HCl standard.)
9.1 Method—The detector is calibrated by adjusting the
7.2.2 Prepare the following HCl calibration standards from
detector output to 147.0 µS/cm for a 1-mM solution of
the 2.00-mM HCl standard stock solution. Use accurate Class
potassium chloride flowing through the conductivity cell at 1
A pipettes and 100-mL plastic volumetric flasks.
mL/min.
HCl Concentration, Volume in 100 mL DI Water,
mM mL 9.1.1 Set up the chromatographic system according to the
instructions in Section 8. Turn on the pump and ensure that the
0.02 1
pump is pumping smoothly.
0.04 2
0.1 5
9.1.2 Monitor the detector output. The conductivity should
0.2 10
be below 1µS/cm. If it is higher, continue flushing out the
0.4 20
system to remove leftover salts until the conductivity stabilizes
2 No dilution below 1 µS/cm. (A higher reading is an indication of either an
incompletely cleaned flow system or of poor deionized water
8. Instrumentation Set-Up
quality and may compromise noise and linearity tests.) Fill the
sample injection loop with DI water and inject. Note the
8.1 Set up the chromatographic system according to the
minimum conductivity reported during the elution of the DI
manufacturer’s recommendation. Also, passivate the conduc-
water through the detector cell. Either calibrate the detector to
tivity cell using the manufacturer’s recommended procedure.
zero using the injected DI water or subtract the conductivity of
Set the flow rate on the pump to 1.0 mL/min or to the flow rate
injected DI water from all subsequent measurements.
normallyusedinyourapplication.Filltheeluentbottlewith18
9.1.3 Fill the sample injection loop with the 1-mM KCl
M-ohm DI water. Connect the outlet of the pump to the
standard and inject the standard. Note the maximum conduc-
injection valve, and the outlet of the injection valve directly to
tivity reported during the elution through the detector cell of
the conductivity cell using as short a length of tubing as is
the 1-mM KCl standard. It should be 147.0 µS/cm. If it is not,
practical. (Standard 0.25-mm (0.01-in.) internal diameter
follow the manufacturer’s procedure for calibrating the con-
HPLC tubing may be used.) Do not install any columns or
ductivity detector so that the reading will be 147.0 µS/cm.
suppressors. To ensure smooth operation of the pump, it is
9.1.4 Some conductivity detectors do not report conductiv-
necessary to supply more pressure than that normally provided
ity directly in siemens, but instead provide a voltage output
by the detector cell and the standard tubing alone. This is
proportional to conductivity. Instead of adjusting the detector
accomplished by installing a 1-m coil of 0.25-mm internal
output, calibrate these detectors by recording the known
diameter narrow bore tubing between the pump and the
conductivity of the calibration solution (147.0 µS/cm for 1 mM
injection valve. Increase the length or decrease the diameter of
KCl), the detector sensitivity range, and the measured voltage
the tubing if the pressure is not high enough to produce smooth
output. (Be sure to subtract the voltage output for a blank of DI
pump operation. Generally, 500 to 1 000 psi will be sufficient.
water.) Divide the known conductivity by the net voltage
The waste line connected to the cell outlet should be of
output reading and multiply all subsequent voltage output
sufficient length to provide enough backpressure on the cell to
readings by this value.
prevent the formation of bubbles inside the cell. Inserting 20
cm of 0.25-mm internal diameter tubing between the cell and
10. Noise and Drift
waste line should provide sufficient backpressure.
10.1 MethodofMeasurement—Noiseanddriftaremeasured
8.2 Install a sample injection loop of approximately 200 µL
under two conditions. Pure DI water is pumped through the
on the injection valve. This can be constructed from1mof
conductivitycellat1mL/minandthenoiseanddriftmeasured.
0.5-mm (0.02-in.) internal diameter tubing. During the tests
The procedure is then repeated using 1 mM KCl. The detector
described in Sections 6 and 7, observe the recorder trace and
output may be sensitive to temperature changes. It is worth-
verify that a plateau is reached after injection of the standard
while to perform this test twice: once with the temperature of
solutions. If no plateau is reached, then a larger sample
the eluents and of the laboratory held as constant as possible,
injection loop is needed.
and once with controlled changes in laboratory temperature of
8.3 If the conductivity detector has a
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