1、Designation: E2677 14Standard Test Method forDetermining Limits of Detection in Explosive TraceDetectors1This standard is issued under the fixed designation E2677; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 In harmony with the Joint Committee for Guides inMetrology (JCGM) and detection concepts of the InternationalUnion of Pure an
3、d Applied Chemistry (IUPAC) (1, 2, 3)2, thistest method uses a series of replicated measurements of ananalyte at dosage levels giving instrumental responses thatbracket the critical value, a truncated normal distributionmodel, and confidence bounds to establish a standard fordetermining practical an
4、d statistically robust limits of detectionto analytes sampled on swabs by explosive trace detectors(ETDs).1.2 Here, the limit of detection (LOD90) is defined to be thelowest mass of a particular compound deposited on a samplingswab for which there is 90 % confidence that a single mea-surement in a p
5、articular ETD will have a true detectionprobability of at least 90 % and a true nondetection probabilityof at least 90 % when measuring a process blank sample.1.3 This particular test method was chosen on the basis ofreliability, practicability, and comprehensiveness across testedETDs, analytes, and
6、 deployment conditions. The calculationsinvolved in this test method are published elsewhere (4), andmay be performed consistently with an interactive web-basedtool available on the National Institute of Standards andTechnology (NIST) site: http:/pubapps.nist.gov/loda.1.4 Intended UsersETD developer
7、s, ETD vendors, ETDbuyers, ETD testers, ETD users (first responders, securityscreeners, and the military), and agencies responsible forpublic safety and enabling effective deterrents to terrorism.1.5 While this test method may be applied to any detectiontechnology that produces numerical output, the
8、 procedureshave been designed for ion mobility spectrometry (IMS) basedETD systems and tested with low vapor pressure explosivecompounds. Compounds are deposited as liquid solutions onswabs and dried before use. As some swabs are absorbent, thisdeposition procedure may not be optimal for those ETDte
9、chnologies that rely on high coverage of analyte on thesurface of the swab. Background interferences introduced tothe test samples were representative of a variety of conditionsexpected during deployment, but these conditions were notintended as comprehensive in representing all possible sce-narios.
10、 The user should be aware of the possibility that untestedscenarios may lead to failure in the determination of a reliableLOD90 value.1.6 UnitsThe values stated in SI units are to be regardedas the standard. No other units of measurement are included inthis standard.1.7 This standard does not purpor
11、t to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Some specifichazards statements are given in Se
12、ction 8 on Hazards.2. Referenced Documents2.1 ASTM Standards:3D6091 Practice for 99 %/95 % Interlaboratory DetectionEstimate (IDE) for Analytical Methods with NegligibleCalibration ErrorE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE200 Practice for Preparation, Standardiz
13、ation, and Storageof Standard and Reagent Solutions for Chemical AnalysisE288 Specification for Laboratory Glass Volumetric FlasksE456 Terminology Relating to Quality and StatisticsE542 Practice for Calibration of Laboratory VolumetricApparatusE691 Practice for Conducting an Interlaboratory Study to
14、Determine the Precision of a Test MethodE969 Specification for Glass Volumetric (Transfer) PipetsE1154 Specification for Piston or Plunger Operated Volu-metric Apparatus1This test method is under the jurisdiction of ASTM Committee E54 onHomeland Security Applications and is the direct responsibility
15、 of SubcommitteeE54.01 on CBRNE Sensors and Detectors.Current edition approved Feb. 1, 2014. Published February 2014. DOI: 10.1520/E2677-14.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.o
16、rg, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E1323 Guide f
17、or Evaluating Laboratory Measurement Prac-tices and the Statistical Analysis of the Resulting DataE2520 Practice for Verifying Minimum Acceptable Perfor-mance of Trace Explosive DetectorsE2655 Guide for Reporting Uncertainty of Test Results andUse of the Term Measurement Uncertainty in ASTM TestMeth
18、ods3. Terminology3.1 Definitions:3.1.1 alarm rule, nuser-selectable explosive trace detector(ETD) response requirements that, if met during an analysis,result in a detection alarm for a particular compound.3.1.1.1 DiscussionAn alarm rule is a logistical pattern inthe detection response matrix for an
19、 analysis. The simplestalarm rule would require only a single positive detectionresponse, whereas a more selective rule (useful for minimizingalpha risk) may require two positive responses in any of threechannels and perhaps a negative response in another channel.3.1.2 alarm threshold, nsee detectio
20、n threshold.3.1.3 alpha, , risk, nprobability of obtaining a positivedetection outcome, or alarm, when analyzing a process blank ina properly-operating ETD.3.1.4 analyte, nthe particular chemical compound underconsideration.3.1.4.1 DiscussionPure analyte is used to make referencesolutions by quantit
21、ative dissolution into a known amount ofsolvent. Quantitative depositions of reference solutions aresubsequently used to prepare reference swabs containingknown amounts of analyte.3.1.5 beta, , risk, nprobability of obtaining a negativedetection outcome, or non-alarm, in a properly operating ETDwhen
22、 analyzing a swab containing analyte at the mass levelcorresponding to the limit of detection.3.1.6 blank, nsample swab devoid of analyte.3.1.6.1 DiscussionIf a swab is prepared using the sameprocedures used in preconditioning the reference swabs andonly pure solvent or a chemical background is depo
23、sited, thisswab is called a process blank.3.1.7 chemical background, nparticular mixture of envi-ronmental and ambient substances that may be sampled by aswab during normal operation of an ETD in a deployment area.3.1.7.1 DiscussionThe presence of certain substances on asample or reference swab may
24、interfere with or suppressexpected ETD responses for particular analytes, hence influ-encing the effective limit of detection (LOD90) values forthose analytes and changing the alpha and beta risks for thedetection process.3.1.8 critical value, CV, ninstrumental response amplitudeat which there is pa
25、rticular confidence that the signal may beattributed to a particular analyte.3.1.8.1 DiscussionThe CV is defined by the desired alphaand beta risks of detection and is a response somewhat belowthe mean response of samples prepared at the limit of detec-tion. A realistic CV is the optimal basis of a
26、single-channeldetection threshold.3.1.9 detection outcome, nbinomial (yes/no) response ofan analysis within a particular channel (or spectral window) inan ETD.3.1.9.1 DiscussionThe channel response is “positive”when the signal in the channel meets or exceeds all detectionthresholds; otherwise, the c
27、hannel response is “negative.”3.1.10 detection threshold, nset of signal characteristics,often user selected, for a particular channel (or spectralwindow) in an ETD.3.1.10.1 DiscussionThese characteristics usually includethe peak amplitude (optimally, the critical value) but may alsoinclude the peak
28、 shape, onset time, duration, and positionwithin a detection window. If the measured signal in thatchannel meets or exceeds the detection threshold settings, thedetection outcome is designated as “positive;” otherwise, theresponse is “negative.” One or more position detections areneeded within the a
29、larm rules to elicit an alarm for a particularanalyte. The alarm threshold for a particular analyte is the sameas the detection threshold if the alarm rule uses only onechannel. If the alarm rule requires two or more positiveresponses, or negative responses in certain channels, the alarmthreshold is
30、 a logistical function of the channel signals in-volved.3.1.11 explosive trace detector, ETD, ndevice used toidentify the presence of small amounts of explosive com-pounds.3.1.11.1 DiscussionETDs are commonly used at airportsby security screeners, who wipe a surface with a swab tocollect residues, a
31、nd then analyze the swab in the ETD.Explosive vapor detectors (EVDs) are a subset of ETDs thatsample air to detect vapors indicative of explosives.3.1.12 explosive vapor detector, EVD, nused to sampleairindoors, outdoors, or within containersto identify va-pors indicative of the presence of explosiv
32、es.3.1.12.1 DiscussionDetected vapors may be explosivecompounds or other chemicals in patterns suggestive of par-ticular explosive formulations.3.1.13 ion mobility spectrometry, IMS, ndetection tech-nology commonly used in commercial ETDs (for othertechnologies, please see Caygill et al (5).3.1.13.1
33、 DiscussionTypically, samples are heated to va-porize trace analytes of interest, which are then selectivelyionized, separated on the basis of ion mobility through air in ananalyzer tube, and detected using a Faraday cup. Raw re-sponses are processed to enhance the chemical signals. Furtherinformati
34、on on IMS may be found in Eiceman and Zarpas (6).3.1.14 limit of detection, LOD, ncommonly accepted asthe smallest amount of a particular substance that can bereliably detected in a given type of medium by a specificmeasurement process.3.1.14.1 DiscussionMay be defined either in terms of theinstrume
35、ntal signal response or the analyte mass that elicits thesignal response. Here, the limit of detection (LOD90) isdefined to be the lowest mass of an analyte deposited on areference swab for which there is 90 % confidence that a singlemeasurement in particular ETD will have a true detectionprobabilit
36、y of at least 90 % and a true nondetection probabilityE2677 142of at least 90 % when measuring a process blank sample.Values of LOD90 are performance measures of a deployeddetection system and provide guidance for setting optimal ETDdetection thresholds in that system.3.1.15 LOD90, nsee limit of det
37、ection.3.1.16 nondetection probability, nsee beta risk.3.1.17 process blank, nsee blank.3.1.18 reference swabs, nsee swabs.3.1.19 significant mass level, SML, nlowest mass in aseries of prepared mass levels that elicits significantly highermean responses in an ETD compared to the mean responsesfrom
38、process blanks.3.1.19.1 DiscussionThe SML is a crude estimate of theLOD90.3.1.20 substrates, nsee swabs.3.1.21 swabs, nalso known as substrates, swipe media,traps, and wipes, swabs are special fabrics made of suchmaterials as cotton, fiberglass, or polymers and are designedfor wiping sample surfaces
39、 and holding residues collected fromthose surfaces.3.1.21.1 DiscussionDistributed by ETD manufacturersand consumable suppliers, swabs have particular propertiesand shapes designed to fit into the sampling inlets of ETDs.Each type of swab has a “sweet spot” for sampling where thedetection of analyte
40、is optimized (Practice E2520). This isgenerally an area about 1 cm in diameter. Please consult withthe manufacturer to confirm the location of the sweet spot.Swabs containing known amounts of analyte deposited in thesweet spot are called reference swabs.3.1.22 swipe media, nsee swabs.3.1.23 traps, n
41、see swabs.3.1.24 wipes, nsee swabs.4. Summary of Test Method4.1 Reference solutions are prepared containing knownconcentrations of a particular analyte.4.2 Standard operating conditions for the ETD are set. Ifneeded, the target analyte is programmed into the ETDdatabase.4.3 OptionalUsing a reproduci
42、ble method, clean swabsare preconditioned with “chemical background.”4.4 The ETD is determined to be in operational readiness.4.5 Exploratory measurements are performed to determinethe significant mass level (SML), which is the lowest level ofanalyte mass on a reference swab that gives a mean respon
43、sesignificantly higher than that from process blanks.4.6 Using the SML as a guide, four mass levels of referenceswabs are prepared that provide appropriate bracketing of theestimated LOD90 value.4.7 Starting at the lowest mass level, replicates of thereference swabs are run on the ETD. In turn, the
44、higher masslevels are run.4.8 Data are evaluated using a validated algorithm accessedthrough a web-based calculator at http:/pubapps.nist.gov/loda.This process returns an estimate of the LOD90 value as well asupper confidence and tolerance limits. Optional tools includedata plotting and outlier test
45、s. The alpha and beta risks may bechanged from the default values.4.9 Guidance is given regarding the setting of an alarmthreshold in an ETD to achieve a reliable balance of alpha andbeta risks.5. Significance and Use5.1 ETDs are used by first responders, security screeners,the military, and law enf
46、orcement to detect and identifyexplosive threats quickly. ETDs typically operate by detectingchemical agents in residues and particles sampled from sur-faces and can have detection limits for some compoundsextending below 1 ng. An ETD is set to alarm when itsresponse to any target analyte exceeds a
47、programmed thresholdlevel for that analyte. Factory settings of such levels typicallybalance sensitivity and selectivity assuming standard operatingand deployment conditions.5.2 ALOD is commonly accepted as the smallest amount ofa particular substance that can be reliably detected in a giventype of
48、medium by a specific measurement process (2, 3). Theanalytical signal from this amount shall be high enough aboveambient background variation to give statistical confidence thatthe signal is real. Methods for determining nominal LODvalues are well known (for example, Hubaux and Vos (7) andPractice D
49、6091), but pitfalls exist in specific applications.Vendors of ETDs often report detection limits for only a singlecompound without defining the meaning of terms or referenceto the method of determination.NOTE 1There are several different “detection limits” that can bedetermined for analytical procedures. These include the minimum detect-able value, the instrument detection limit, the method detection limit, thelimit of recognition, and the limit of quantitation. Even when the sameterminology is used, there can be differences in the LOD ac
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