ASTM E1657-98(2019)
(Practice)Standard Practice for Testing Variable-Wavelength Photometric Detectors Used in Liquid Chromatography
Standard Practice for Testing Variable-Wavelength Photometric Detectors Used in Liquid 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 should be obtained under the same operating conditions. It should also be noted that to completely specify a detector’s capability, 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 that they may be used regardless of the ultimate operating parameters.
4.2 Linearity and response time of the recorder or other readout device used should be such that they do not distort or otherwise interfere with the performance of the detector. This requires adjusting the gain, damping, and calibration in accordance with the manufacturer's directions. If additional electronic filters or amplifiers are used between the detector and the final readout device, their characteristics should also first be established.
SCOPE
1.1 This practice covers the testing of the performance of a variable-wavelength photometric detector (VWPD) used as the detection component of a liquid-chromatographic (LC) system operating at one or more wavelengths in the range 190 to 800 nm. Many of the measurements are made at 254 nm for consistency with Practice E685. Measurements at other wavelengths are optional.
1.2 This practice is intended to describe the performance of the detector both independently of the chromatographic system (static conditions) and with flowing solvent (dynamic conditions).
1.3 For general liquid chromatographic procedures, consult Refs (1-9).2
1.4 For general information concerning the principles, construction, operation, and evaluation of liquid-chromatography detectors, see Refs (10, 11) in addition to the sections devoted to detectors in Refs (1-7).
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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.
1.7 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: E1657 − 98 (Reapproved 2019)
Standard Practice for
Testing Variable-Wavelength Photometric Detectors Used in
Liquid Chromatography
This standard is issued under the fixed designation E1657; 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 the testing of the performance of a 2.1 ASTM Standard:
variable-wavelengthphotometricdetector(VWPD)usedasthe E685Practice for Testing Fixed-Wavelength Photometric
detection component of a liquid-chromatographic (LC) system Detectors Used in Liquid Chromatography
operating at one or more wavelengths in the range 190 to 800
nm. Many of the measurements are made at 254 nm for
3. Terminology
consistency with Practice E685. Measurements at other wave-
3.1 Definitions:
lengths are optional.
3.1.1 absorbance calibration—the procedure that verifies
1.2 This practice is intended to describe the performance of that the absorbance scale is correct within 65%.
thedetectorbothindependentlyofthechromatographicsystem
3.1.2 drift—the average slope of the noise envelope ex-
(static conditions) and with flowing solvent (dynamic condi-
pressed in absorbance units per hour (AU/h) as measured over
tions).
a period of 1 h.
1.3 For general liquid chromatographic procedures, consult
3.1.3 dynamic—under conditions of a flow rate of 1.0
Refs (1-9).
mL/min.
1.4 For general information concerning the principles,
3.1.4 linear range—of a VWPD,therangeofconcentrations
construction, operation, and evaluation of liquid-
of a test substance in a test solvent over which the ratio of
chromatography detectors, see Refs (10, 11) in addition to the
response of the detector versus concentration of test substance
sections devoted to detectors in Refs (1-7).
is constant to within 5% as determined from the linearity plot
specified in 7.1.2 and illustrated in Fig. 1. The linear range
1.5 The values stated in SI units are to be regarded as
should be expressed as the ratio of the upper limit of linearity
standard. No other units of measurement are included in this
obtained from the plot to either (a) the lower linear
standard.
concentration, or (b) the minimum detectable concentration, if
1.6 This standard does not purport to address all of the
the minimum detectableconcentrationisgreaterthanthelower
safety concerns, if any, associated with its use. It is the
linear concentration.
responsibility of the user of this standard to establish appro-
3.1.5 long-term noise—the maximum amplitude in AU for
priate safety, health, and environmental practices and deter-
all random variations of the detector signal of frequencies
mine the applicability of regulatory limitations prior to use.
between6and60cyclesperhour(0.1and1.0cyclespermin).
1.7 This international standard was developed in accor-
3.1.5.1 Discussion—Itrepresentsnoisethatcanbemistaken
dance with internationally recognized principles on standard-
for a late-eluting peak. This noise corresponds to the observed
ization established in the Decision on Principles for the
noise only and may not always be present.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
3.1.6 minimum detectability—of a VWPD, that concentra-
Barriers to Trade (TBT) Committee.
tion of a specific solute in a specific solvent that results in a
detector response corresponding to twice the static short-term
1 noise.
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.19 on Separation Science.
Current edition approved Dec. 1, 2019. Published December 2019. Originally
approved in 1994. Last previous edition approved in 2011 as E1657–98(2011). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/E1657–98R19. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1657 − 98 (2019)
the reproducibility of absorbance values when the detector is
reset to a wavelength maximum of a known test substance.
4. 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 should be obtained
under the same operating conditions. It should also be noted
that to completely specify a detector’s capability, its perfor-
mance 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 that they may be used
regardless of the ultimate operating parameters.
4.2 Linearity and response time of the recorder or other
readout device used should be such that they do not distort or
otherwise interfere with the performance of the detector. This
requires adjusting the gain, damping, and calibration in accor-
dance with the manufacturer’s directions. If additional elec-
tronicfiltersoramplifiersareusedbetweenthedetectorandthe
FIG. 1 Example of Linearity Plot for a Variable-Wavelength De-
final readout device, their characteristics should also first be
tector
established.
5. Noise and Drift
3.1.6.1 Discussion—The static short-term noise is a mea-
5.1 Test Conditions—Pure, degassed methanol shall be
surement of peak-to-peak noise.Astatistical approach to noise
used in the sample cell. Air or nitrogen shall be used in the
suggeststhatavalueofthreetimestherms(root-mean-square)
reference cell if there is one. Nitrogen is preferred where the
noise would insure that any value outside this range would not
presenceofhigh-voltageequipmentmakesitlikelythatthereis
be noise with a confidence level of greater than 99%. Since
ozone in the air. Protect the entire system from temperature
peak-to-peak noise is approximately five times the rms noise
fluctuations because these will lead to detectable drift.
(12), the minimum detectability defined in this practice is a
5.1.1 The detector should be located at the test site and
more conservative estimate.
turned on at least 24 h before the start of testing. Insufficient
3.1.7 response time (speed of output)— the detector, the
warm-upmayresultindriftinexcessoftheactualvalueforthe
time required for the detector output to change from 10% to
detector. The detector wavelength should be set to 254 nm.
90% of the new equilibrium value when the composition of
5.2 Methods of Measurement:
the mobile phase is changed in a stepwise manner, within the
linear range of the detector. 5.2.1 Connect a suitable device (see Note 1) between the
pumpandthedetectortoprovideatleast75kPa(500psi)back
3.1.7.1 Discussion—Because the detector volume is very
small and the transport rate is not diffusion dependent, the pressure at 1.0 mL/min flow of methanol. Connect a short
length(about100mm)of0.25mm(0.01in.)internal-diameter
response time is generally fast enough to be unimportant. It is
generally comparable to the response time of the recorder and stainless steel tubing to the outlet tube of the detector to retard
bubble formation. Connect the recorder to the proper detector
dependent on the response time of the detector electrometer
output channels.
and on the recorder amplifier. Factors that affect the observed
response time include the true detector response time, elec-
NOTE 1—Suggested devices include (a)2to4mof0.1mm (0.004 in.)
tronic filtering, and system band-broadening.
internal-diameter stainless steel tubing, (b) about 250 mm of 0.25 to 0.5
mm(0.01to0.02in.)internal-diameterstainlesssteeltubingcrimpedwith
3.1.8 short-term noise—the maximum amplitude, peak to
pliersorcutters,or(c)aconstantback-pressurevalvelocatedbetweenthe
peak, inAU for all random variations of the detector signal of
pump and the injector.
a frequency greater than one cycle per minute.
5.2.2 Repeatedly rinse the reservoir and chromatographic
3.1.8.1 Discussion—Itdeterminesthesmallestsignaldetect-
system, including the detector, with degassed methanol to
ablebyaVWPD,limitstheprecisionattainableinquantitation
remove from the system all other solvents, any soluble
of trace-level samples, and sets the lower limit on linearity.
material, and any entrained gasses. Fill the reservoir with
This noise corresponds to the observed noise only.
methanolandpumpthissolventthroughthesystemforatleast
3.1.9 static—under conditions of no flow.
30 min to complete the system cleanup.
3.1.10 wavelength accuracy—the deviation of the observed
5.2.3 Air or nitrogen is used in the reference cell, if any.
wavelength maximum from the maximum of a known test
Ensure that the cell is clean, free of dust, and completely dry.
substance.
3.1.11 wavelength precision—a measure of the ability of a
Distilled-in-glass or liquid-chromatography grade. Complete freedom from
VWPD to return to the same spectral position as measured by particles may require filtration, for example, through a 0.45 µm membrane filter.
E1657 − 98 (2019)
5.2.4 To perform the static test, cease pumping and allow these conditions, during which time the ambient temperature
thechromatographicsystemtostabilizeforatleast1hatroom should not change by more than 2°C.
temperature without flow. Set the attenuator at maximum
NOTE2—Timeconstantisconvertedtoresponsetimebymultiplyingby
sensitivity (lowest attenuation), that is, the setting for the
the factor 2.2. The effect of electronic filtering on observed noise may be
smallest value of absorbance units full-scale (AUFS). Adjust studied by repeating the noise measurements for a series of response-time
settings.
the response time as close as possible to 2 s for a VWPD that
has a variable response time (see Note 2). Record the response 5.2.5 Draw pairs of parallel lines, each pair corresponding
time used. Adjust the detector output to near midscale on the to between 0.5 and 1 min in length, to form an envelope of all
readout device. Record at least1hof detector signal under observed random variations over any 15 min period (see Fig.
FIG. 2 Example for the Measurement of the Noise and Drift of a VWD (Chart Recorder Output)
E1657 − 98 (2019)
2). Draw the parallel lines in such a way as to minimize the absorption spectra. The stated linear range of the method may
distance between them. Measure the vertical distance, in AU, be compromised if the wavelength is inaccurate. Further, the
between the lines. Calculate the average value over all the precision of adjusting the detector to the same wavelength
segments.Dividethisvaluebythecelllengthincentimetersto should also be known. The wavelength of a VWPD is
obtain the static short-term noise. determinedbythemonochromatorandtheopticalalignmentof
5.2.6 Nowmarkthecenterofeachsegmentoverthe15min the detector. The optical alignment is performed by the
period of the static short-term noise measurement. Draw a manufacturer and usually does not need readjustment. Some
series of parallel lines encompassing these centers, each pair detectorsrequirealignmentofthelampafterreplacement.This
correspondingto10mininlength,andchoosethatpairoflines procedure verifies that the detector is properly aligned and
whose vertical distance apart is greatest (see Fig. 2). Divide meets the manufacturer’s specifications for wavelength accu-
this distance in AU by the cell length in centimeters to obtain racy and precision.
the static long-term noise.
6.2 Method of Measurement—Wavelength Accuracy—For
5.2.7 Draw the pair of parallel lines that minimizes the
thedeterminationofthe wavelength accuracy of a VWPD, (13)
vertical distance separating these lines over the 1 h of mea-
a solution of a compound with known absorbance maxima is
surement (Fig. 2). The slope of either line is the static drift
introduced into the cell. The measured maxima are compared
expressed in AU/h.
to the known maxima for the compound. There are several
5.2.8 Set the pump to deliver 1.0 mL/min under the same 5
acceptable compounds and solvents. The following procedure
conditions of tubing, solvent, and temperature as in 5.2.1 –
is recommended (Note 3).
5.2.3.Allow 15 min for the system to stabilize. Record at least
NOTE 3—The recommended procedure is covered under U.S. Patent
1hofsignalundertheseflowingconditions,duringwhichtime
4836673. The American Society for Testing and Materials takes no
the ambient temperature should not change by more than 2°C.
position respecting the validity of any patent rights asserted in connection
5.2.9 Draw pairs of parallel lines, measure the vertical
with any item mentioned in this practice. Users of this practice are
distances, and calculate the dynamic short-term noise follow-
expressly advised that determination of the validity of any such patent
rights, and the risk of infringement of such rights, are entirely their own
ing the procedure of 5.2.5.
responsibility. Alternative procedures will be considered.
5.2.10 Make the measurement for the dynamic long-term
noise following the procedure outlined in 5.2.6. 6.2.1 Prepare the test solution. For example, dissolve2gof
6 7
5.2.11 Draw the pair of parallel lines as directed in 5.2.7. erbiumperchloratehexahydrate in25mLwater. Thenominal
The slope of these lines is the dynamic drift. concentrationis0.14M.Filterthesolutionwithanappropriate
5.2.12 The actual noise of the system may be larger or filter to ensure the sample is free of particles.
smaller than the observed values, depending upon the method
NOTE 4—This can be conveniently done by adding water toa2g vial
of data collection, or signal monitoring of the detector, since
of erbium perchlorate hexahydrate to dissolve the solid. Transfer the
observed noise is a function of the frequency, speed of
contents to a 25 mL volumetric flask and make up to volume with water.
While reasonable care should be observed in transferring the dissolved
response, and bandwidth of the readout device.
erbium perchlorate into the volumetric flask, the final solution is not used
quantitatively.
6. Wavelength Accuracy
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