ASTM E1511-93(2000)
(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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:E1511–93 (Reapproved 2000)
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 the
upper limit may instead be limited by the maximum full-scale
inverse of the resistance measured between two electrodes in a
deflection on the detector’s least sensitive output range.)
cell, expressed in units of siemens (S), equal to inverse ohms.
3.2.9 long-term noise—the maximum amplitude in nano
3.2.2.1 Discussion—The term resistance refers specifically
siemenspercentimetreforallrandomvariationsofthedetector
to the dc resistance to ionic current, independent of the
output of frequencies between 2 and 60 cycles per hour.
capacitive reactance at the interfaces between the electrodes
3.2.9.1 Discussion—Long-term noise represents noise
and the solution.
which can be mistaken for eluting peaks.
3.2.3 conductivity—since the conductance is dependent on
3.2.10 minimum detectability—of a conductivity detector,
both the conductive properties of the solution and on the
that concentration of solute in a specific solvent which corre-
dimensions of the electrodes and the cell, the conductivity (k)
sponds to twice the short-term noise.
of the solution is defined to be independent of electrode and
3.2.10.1 Discussion—Because of the difficulty of pumping
cell dimensions. Specifically,
solvents through the chromatographic system without any
k5 G (1) contamination of the solvents from the system, this quantity
A
can only be measured with solutes retained by a column. Since
minimum detectability is dependent on the chromatographic
This practice is under the jurisdiction of ASTM Committee E13 on Molecular system used, it is not measured in this practice. However, if the
Spectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-
minimum detectability of a solute is measured on one system
tography.
with one detector, the minimum detectability can be predicted
Current edition approved Jan. 15, 1993. Published March 1993.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1511
when other detectors are tested on the same system by 5.2 Although it is possible to observe each of the several
comparing the measured values of short-term noise. characteristics of a detector under different and unique condi-
3.2.11 response factor—of a conductivity detector, the mea- tions, it is the intent of this practice that a complete set of
sured conductivity response of a solute divided by the solute detector specifications should be obtained at the same operat-
concentration. ing conditions, including the setup used for testing, flow rates,
3.2.12 response time of the detector—the time required for andtemperatures.Itshouldbenotedthattospecifyadetector’s
capability completely, its performance should be measured at
the output of the detector to change from 10 % to 90 % of the
new equilibrium value when the composition of the eluent is several sets of conditions within the useful range of the
detector. The terms and tests described in this practice are
changed in a stepwise manner, within the linear range of the
detector. sufficiently general so that they may be used at whatever
conditions may be chosen for other reasons.
3.2.12.1 Discussion—Aslow response time has the effect of
limiting resolution for efficient peaks such as early eluting
6. Reagents
peaks and those from highly efficient columns or microbore
columns. Response time is generally dependent on three
6.1 Reagent chemicals are reagent grade or better.
factors: (a) cell volume, (b) volume of heat transfer tubing
6.1.1 Deionized Water, (DI water), 18 M-ohm.
leading to the cell, and (c) electronic filtering of the output.
6.1.2 Potassium Chloride, (KCl) dry powder.
3.2.13 sensitivity—thedetectorresponsedividedbyconcen-
6.1.3 Hydrochloric Acid, (HCl) standard 0.1000 N solution.
tration, which is also the response factor (11.1.1).
3.2.13.1 Discussion—Sensitivity is therefore by definition 7. Preparation of Standards
the same for all properly calibrated conductivity detectors.
7.1 Potassium Chloride Standards:
(Sensitivity is often confused with minimum detectability,
7.1.1 Prepare a 10-mM KCl standard stock solution. Weigh
which is dependent on both sensitivity and noise.) Therefore,
out 0.7455 g KCl (desiccated) and dissolve it in 18 M-ohm DI
the calibration of the detector should be measured, and if
water in a 1-Lplastic volumetric flask. Fill the flask to 1 Lwith
necessary, adjusted. Follow the manufacturer’s procedure for
DI water.
calibrating the detector. The procedure in Section 9 is used by
7.1.2 Prepare KCl standards from the 10-mM KCl standard
many manufacturers and is useful for the tests in this practice.
stock solution. Using accurate Class A pipettes, pipette the
3.2.14 short-term noise—the maximum amplitude in nano
volumes of the 10-mM standard stock solution listed below
siemenspercentimetreforallrandomvariationsofthedetector
into 100-mL plastic volumetric flasks. For the 1-mM KCl
output of a frequency greater than one cycle per minute.
standard,filla100-mLplasticvolumetricflaskwiththe10-mM
3.2.14.1 Discussion—Short-term noise determines the
KCl solution and transfer to a 1-Lplastic volumetric flask. Fill
smallest signal detectable by a conductivity detector, limits the
to the line with DI water.
precision available for the determination of trace samples, and
KCl Concentration, Volume in 100 mL DI Water,
may set the lower limit of linearity.
mm mL
0.05 0.5
4. Summary of Practice
0.1 1
0.2 2
4.1 Four different tests are performed to characterize a
0.5 5
detector.
1 100 mL in 1 L
4.1.1 Noise and drift are measured while a solution is 220
flowing through the detector cell. The test is performed using
10 mM No dilution
two different solutions: deionized water (DI) and 1 mM
7.2 Hydrochloric Acid Standards:
potassium chloride (KCl).
7.2.1 Prepare a 2.00-mM HCl standard stock solution by
4.1.2 Linear range is determined by preparing a plot of
diluting 20.0 mL of standard 0.1000 N HCl into a 1-L plastic
response factor versus the log of solute concentration using
volumetric flask and filling to the line with DI water. If
standard solutions of KCl and hydrochloric acid (HCl) as
standard 0.1000 N HCl is not available, a 0.10-mM HCl
solutes.
solution can be prepared by diluting 8.3 mL of 12 N (37 %)
4.1.3 Dependence of response on flow rate is measured by
concentration HCl into 1 L of DI water. (The concentration of
pumping 1 mM KCl through the conductivity cell at several
this solution will be less accurate than that prepared from
flow rates and measuring the detector output.
0.1000 N HCl standard.)
4.1.4 Response time is measured by measuring the time
7.2.2 Prepare the following HCl calibration standards from
required for the detector output to change from that measured
the 2.00-mM HCl standard stock solution. Use accurate Class
with DI water to that measured with 1 mM KCl.
A pipettes and 100- mL plastic volumetric flasks.
HCl Concentration, Volume in 100 mL DI Water,
5. Significance and Use
mM mL
5.1 This practice is intended to describe the performance of
0.02 1
a conductivity detector independent of the chromatographic
0.04 2
system in terms that the analyst can use to predict overall
0.1 5
system performance when the detector is coupled to the 0.2 10
0.4 20
column and other chromatography system components.
E1511
below 1 µS/cm. (A higher reading is an indication of either an
2 No dilution
incompletely cleaned flow system or of poor deionized water
quality and may compromise noise and linearity tests.) Fill the
8. Instrumentation Set-Up
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
10. Noise and Drift
cm of 0.25-mm internal diameter tubing between the cell and
waste line should provide sufficient backpressure.
10.1 Method of Measurement—Noise and drift are mea-
8.2 Install a sample injection loop of approximately 200 µL
sured under two conditions. Pure, deionized water is pumped
on the injection valve. This can be constructed from1mof
through the conductivity cell at 1 mL/min and the noise and
0.5-mm (0.02-in.) internal diameter tubing. During the tests
drift measured. The procedure is then repeated using 1 mM
described in Sections 6 and 7, observe the recorder trace and
KCl. The detector output may be sensitive to temperature
verify that a plateau is reached after injection of the standard
changes. It is worthwhile to perform this test twice: once with
solutions. If no plateau is reached, then a larger sample
the temperature of the eluents and of the laboratory held as
injection loop is needed.
constant as possible, and once with controlled changes in
8.3 If the conductivity detector has a setting for temperature
laboratory temperature of approximately 5°C. This may be
compensation, set it to 2.0. If not, the DI water eluent and all
accomplished by cycling on and off a room heater or air
of the test solutions should be thermostated as close as possible
conditioner.
to 25°C. Or, the detector cell may be thermostated at a higher
10.1.1 Set up the chromatographic system as described in
temperature but be calibrated as if the cell were at 25°C. If the
Section 8. Calibrate the detector according to the procedure in
cell is thermostated, ensure that the cell temperature has
Section 9. Pump DI water through the system for at least1hor
stabilized. Refer to the manufacturer’s procedure for cell
until the detector output has stabilized below 1 µS/cm. Set the
temperature stabilization. Turn off any output filtering on the
detector to its maximum sensitivity setting and adjust the
detector. The output from the detector should be monitored on
detector output to approximately midscale on the recorder.
a strip-cha
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.