ASTM E1511-93
(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
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 the standard.
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Designation: E 1511 – 93
Standard Practice for
Testing Conductivity Detectors Used in Liquid and Ion
Chromatography
This standard is issued under the fixed designation E 1511; 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 where 1 is the distance between two planer disk electrodes
and A is the electrode’s surface area.
1.1 This practice covers the testing of the performance of
3.2.3.1 Discussion—In liquid and ion chromatography, cell
conductivity detectors used as the detection component of a
dimensions are commonly measured in centimetres, so the
liquid or ion chromatography system.
units of k are S/cm. (Alternatively, the SI units of S/m may be
1.2 The values stated in SI units are to be regarded as the
used. S/m = 100 S/cm.)
standard.
3.2.4 drift—the average slope of the noise envelope ex-
2. Referenced Documents pressed in nano siemens per centimetre per hour as measured
over a period of 1 h.
2.1 ASTM Standards:
3.2.5 equivalent conductivity— of an ionic solute, the con-
E 1151 Practice for Ion Chromatography Terms and Rela-
tribution of the solute to the total conductivity of the solution,
tionships
measured in microsiemens per centimetre, divided by its
3. Terminology
concentration in milliequivalents/litre.
3.2.6 flow dependence rate—the change in measured con-
3.1 See Practice E 1151.
ductivity as a function of flow rate.
3.2 Definitions:
3.2.7 limiting equivalent conductivity—of an ionic solute,
3.2.1 cell constant—the cell constant (K) of a conductivity
its equivalent conductivity extrapolated to infinite dilution.
cell is equal to 1/ A,so k =GK.
3.2.8 linear range—of a conductivity detector for a given
3.2.1.1 Discussion—If the cell constant of the flow-through
solute in a specific solvent, the concentration range of solute
cell used is equal to one, then the conductivity equals the
for which the detector response factor is within 5 % of the
conductance. Although the cell constant is often specified for
response factor in the middle of the range as determined from
conductivity detectors, there is little practical value in knowing
the linearity plot specified in Section 11.
the constant as long as the detector is properly calibrated for
3.2.8.1 Discussion—The lower limit may be limited by
conductivity.
noise, and the upper limit by deviation from linearity. (The
3.2.2 conductance—the conductance ( G) of a solution is
upper limit may instead be limited by the maximum full-scale
the inverse of the resistance measured between two electrodes
deflection on the detector’s least sensitive output range.)
in a cell, expressed in units of siemens (S), equal to inverse
3.2.9 long-term noise—the maximum amplitude in nano
ohms.
siemens per centimetre for all random variations of the detector
3.2.2.1 Discussion—The term resistance refers specifically
output of frequencies between 2 and 60 cycles per hour.
to the dc resistance to ionic current, independent of the
3.2.9.1 Discussion—Long-term noise represents noise
capacitive reactance at the interfaces between the electrodes
which can be mistaken for eluting peaks.
and the solution.
3.2.10 minimum detectability— of a conductivity detector,
3.2.3 conductivity—since the conductance is dependent on
that concentration of solute in a specific solvent which corre-
both the conductive properties of the solution and on the
sponds to twice the short-term noise.
dimensions of the electrodes and the cell, the conductivity (k)
3.2.10.1 Discussion—Because of the difficulty of pumping
of the solution is defined to be independent of electrode and
solvents through the chromatographic system without any
cell dimensions. Specifically,
contamination of the solvents from the system, this quantity
k5 G (1) can only be measured with solutes retained by a column. Since
A
minimum detectability is dependent on the chromatographic
system used, it is not measured in this practice. However, if the
This practice is under the jurisdiction of ASTM Committee E13 on Molecular
minimum detectability of a solute is measured on one system
Spectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-
with one detector, the minimum detectability can be predicted
tography.
when other detectors are tested on the same system by
Current edition approved Jan. 15, 1993. Published March 1993.
comparing the measured values of short-term noise.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1511
3.2.11 response factor—of a conductivity detector, the mea- detector specifications should be obtained at the same operat-
sured conductivity response of a solute divided by the solute ing conditions, including the setup used for testing, flow rates,
concentration. and temperatures. It should be noted that to specify a detector’s
3.2.12 response time of the detector—the time required for capability completely, its performance should be measured at
the output of the detector to change from 10 % to 90 % of the several sets of conditions within the useful range of the
new equilibrium value when the composition of the eluent is detector. The terms and tests described in this practice are
changed in a stepwise manner, within the linear range of the sufficiently general so that they may be used at whatever
detector. conditions may be chosen for other reasons.
3.2.12.1 Discussion—A slow response time has the effect of
6. Reagents
limiting resolution for efficient peaks such as early eluting
6.1 Reagent chemicals are reagent grade or better.
peaks and those from highly efficient columns or microbore
6.1.1 Deionized Water, (DI water), 18 M-ohm.
columns. Response time is generally dependent on three
6.1.2 Potassium Chloride, (KCl) dry powder.
factors: (a) cell volume, (b) volume of heat transfer tubing
6.1.3 Hydrochloric Acid, (HCl) standard 0.1000 N solution.
leading to the cell, and ( c) electronic filtering of the output.
3.2.13 sensitivity—the detector response divided by concen-
7. Preparation of Standards
tration, which is also the response factor (11.1.1).
7.1 Potassium Chloride Standards:
3.2.13.1 Discussion—Sensitivity is therefore by definition
7.1.1 Prepare a 10-mM KCl standard stock solution. Weigh
the same for all properly calibrated conductivity detectors.
out 0.7455 g KCl (desiccated) and dissolve it in 18 M-ohm DI
(Sensitivity is often confused with minimum detectability,
water in a 1-L plastic volumetric flask. Fill the flask to 1 L with
which is dependent on both sensitivity and noise.) Therefore,
DI water.
the calibration of the detector should be measured, and if
7.1.2 Prepare KCl standards from the 10-mM KCl standard
necessary, adjusted. Follow the manufacturer’s procedure for
stock solution. Using accurate Class A pipettes, pipette the
calibrating the detector. The procedure in Section 9 is used by
volumes of the 10-mM standard stock solution listed below
many manufacturers and is useful for the tests in this practice.
into 100-mL plastic volumetric flasks. For the 1-mM KCl
3.2.14 short-term noise—the maximum amplitude in nano
standard, fill a 100-mL plastic volumetric flask with the 10-mM
siemens per centimetre for all random variations of the detector
KCl solution and transfer to a 1-L plastic volumetric flask. Fill
output of a frequency greater than one cycle per minute.
to the line with DI water.
3.2.14.1 Discussion—Short-term noise determines the
KCl Concentration, Volume in 100 mL DI Water,
smallest signal detectable by a conductivity detector, limits the
mm mL
precision available for the determination of trace samples, and
0.05 0.5
may set the lower limit of linearity.
0.1 1
0.2 2
4. Summary of Practice
0.5 5
1 100 mL in 1 L
4.1 Four different tests are performed to characterize a
detector.
4.1.1 Noise and drift are measured while a solution is
10 mM No dilution
flowing through the detector cell. The test is performed using
7.2 Hydrochloric Acid Standards:
two different solutions: deionized water (DI) and 1 mM
7.2.1 Prepare a 2.00-mM HCl standard stock solution by
potassium chloride (KCl).
diluting 20.0 mL of standard 0.1000 N HCl into a 1-L plastic
4.1.2 Linear range is determined by preparing a plot of
volumetric flask and filling to the line with DI water. If
response factor versus the log of solute concentration using
standard 0.1000 N HCl is not available, a 0.10-mM HCl
standard solutions of KCl and hydrochloric acid (HCl) as
solution can be prepared by diluting 8.3 mL of 12 N (37 %)
solutes.
concentration HCl into 1 L of DI water. (The concentration of
4.1.3 Dependence of response on flow rate is measured by
this solution will be less accurate than that prepared from
pumping 1 mM KCl through the conductivity cell at several
0.1000 N HCl standard.)
flow rates and measuring the detector output.
7.2.2 Prepare the following HCl calibration standards from
4.1.4 Response time is measured by measuring the time
the 2.00-mM HCl standard stock solution. Use accurate Class
required for the detector output to change from that measured
A pipettes and 100- mL plastic volumetric flasks.
with DI water to that measured with 1 mM KCl.
HCl Concentration, Volume in 100 mL DI Water,
mM mL
5. Significance and Use
0.02 1
5.1 This practice is intended to describe the performance of
0.04 2
a conductivity detector independent of the chromatographic
0.1 5
system in terms that the analyst can use to predict overall
0.2 10
0.4 20
system performance when the detector is coupled to the
column and other chromatography system components.
2 No dilution
5.2 Although it is possible to observe each of the several
8. Instrumentation Set-Up
characteristics of a detector under different and unique condi-
tions, it is the intent of this practice that a complete set of 8.1 Set up the chromatographic system according to the
E 1511
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.
normally used in your application. Fill the eluent bottle with 18 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
10. Noise and Drift
cm of 0.25-mm internal diameter tubing between the cell and
10.1 Method of Measurement—Noise and drift are mea-
waste line should provide sufficient backpressure.
sured under two conditions. Pure, deionized water is pumped
8.2 Install a sample injection loop of approximately 200 μL
through the conductivity cell at 1 mL/min and the noise and
on the injection valve. This can be constructed from1mof
drift measured. The procedure is then repeated using 1 mM
0.5-mm (0.02-in.) internal diameter tubing. During the tests
KCl. The detector output may be sensitive to temperature
described in Sections 6 and 7, observe the recorder trace and
changes. It is worthwhile to perform this test twice: once with
verify that a plateau is reached after injection of the standard
the temperature of the eluents and of the laboratory held as
solutions. If no plateau is reached, then a larger sample
constant as possible, and once with controlled changes in
injection loop is needed.
laboratory temperature of approximately 5°C. This may be
8.3 If the conductivity detector has a setting for temperature
accomplished by cycling on and off a room heater or air
compensation, set it to 2.0. If not, the DI water eluent and all
conditioner.
of the test solutions should be thermostated as close as possible
10.1.1 Set up the chromatographic system as described in
to 25°C. Or, the detector cell may be thermostated at a higher
Section 8. Calibrate the detector according to the procedure in
temperature but be calibrated as if the cell were at 25°C. If the
Section 9. Pump DI water through the system for at least1hor
cell is thermostated, ensure that the cell temperature has
until the detector output has stabilized below 1 μS/cm. Set the
stabilized. Refer to the manufacturer’s procedure for cell
detector to its maximum sensitivity setting and adjust the
temperature stabilization. Turn off any output filtering on the
detector output to approximately midscale on the recorder.
detector. The output from the detector should be monitored on
Adjust the response time or time constant of the detector output
a strip-chart recorder, integrator, or computer. The calibration
filter to1sortothe setting closest to 1 s. Record the baseline
and linearity tests can be performed with a voltmeter monitor-
for at least 1 h. If the detecto
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