1、Designation: F2714 08 (Reapproved 2013)Standard Test Method forOxygen Headspace Analysis of Packages Using FluorescentDecay1This standard is issued under the fixed designation F2714; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. 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 This test method covers a procedure for determinationof the oxygen concentration in the headspace within a
3、 sealedpackage without opening or compromising the integrity of thepackage.1.2 This test method requires that chemically coated com-ponents be placed on the inside surface of the package beforeclosing.1.3 The package must be either transparent, translucent, or atransparent window must be affixed to
4、the package surfacewithout affecting the packages integrity.1.4 As this test method determines the oxygen headspaceover time, the oxygen permeability can easily be calculated asingress per unit time as long as the volume of the container isknown.1.5 The values stated in SI units are to be regarded a
5、sstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport 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
6、 applica-bility of regulatory limitations prior to use.2. Summary of Test Method2.1 Chemically coated components (dots) are affixed to theinside surface of the package to be tested.2.2 The package is gas flushed to a reduced level of oxygeneither manually or by subjecting the package to a fillingope
7、ration.2.3 A pulsing light source is directed through the package atthe chemically treated dot (the package must be transparent,translucent or contain a window through which the light canpass).2.4 The fluorescent response from the dot is monitored andthe decay rate determined.2.5 The internal oxygen
8、 content of the package is deter-mined by comparing the measured decay rate to the decay rateobserved with known oxygen concentrations.3. Significance and Use3.1 The oxygen content of a packages headspace is animportant determinant of the packaging protection afforded bybarrier materials. The packag
9、e under test is typically MAP(modified atmosphere packaging) packaged.3.2 Oxygen content is a key contributor to off-flavors andspoilage of various products, such as chemicals, food andpharmaceuticals.3.3 The method determines the oxygen in a closed packageheadspace. This ability has application in:
10、3.3.1 Package Permeability StudiesThe change of head-space composition over a known length of time allows thecalculation of permeation. Since the headspace oxygen ismeasured as a percentage, the volume of the containersheadspace must be known to allow conversion into a quantitysuch as millilitres (m
11、l) of oxygen. The use of this approach tomeasure permeation generally applies to empty package sys-tems only as oxygen uptake or outgassing of containedproducts could affect results.3.3.2 Leak DetectionIf the headspace contains more oxy-gen than expected or is increasing faster than expected, a leak
12、can be suspected. A wide variety of techniques can beemployed to verify that a leak is present and to identify itslocation. If necessary or of interest, a leak rate may becalculated with known headspace volume and measured oxy-gen concentration change over time.3.3.3 Effcacy of the MAP Packaging Pro
13、cessIf the head-space oxygen concentration is found to be higher than expectedsoon after packaging, the gas flushing process may not beworking as well as expected. Various techniques can evaluatewhether the MAP system is functioning properly.3.3.4 Storage StudiesAs the method is non-destructive,the
14、headspace can be monitored over time on individualsamples to insure that results of storage studies such as shelflife testing are correctly interpreted.1This test method is under the jurisdiction of ASTM Committee F02 on FlexibleBarrier Packaging and is the direct responsibility of Subcommittee F02.
15、40 onPackage Integrity Test Methods.Current edition approved Aug. 1, 2013. Published September 2013. Originallyapproved in 2008. Last previous edition approved in 2008 as F2714 08. DOI:10.1520/F2714-08R13.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2
16、959. United States14. Discussion4.1 Oxygen sensing based on fluorescence is well estab-lished. The typical indicators used are ruthenium complexesand porphyrins both of which are compatible with lightemitting diodes (LEDs). In one oxygen sensitive coating, tris(4,7 biphenyl 1,10 phenanthroline) ruth
17、enium chloride is useddue to its stability, long lifetime, and strong absorption between400 nm and 500 nm in the blue region of the spectrum. Theabsorption peak is compatible with high brightness blue LEDsor blue semiconductor lasers. The emission peak is at 600 nmin the red region of the spectrum a
18、nd is detected by aphotomultiplier tube or a photo detector to offer the flexibilityof a large dynamic range and fast response time. The rutheniumcomplex is immobilized in a highly chemically resistantsubstrate.4.2 The principle of fluorescence quenching is based on theexcited state characteristics
19、of a specific dye. Dynamic quench-ing is the transfer of energy from a fluorescent dye in itsexcited state to oxygen in the surrounding medium. The energyconsumed by oxygen will be dissipated as heat after a shorttime and the whole process can repeat itself indefinitelywithout consuming oxygen.4.3 T
20、he ruthenium complex is excited with blue light froman LED. Short pulses of blue light from the LED are absorbedby the ruthenium complex. In the absence of oxygen, theruthenium complex will emit light in the red region of thespectrum. The average time between the absorption of the bluephoton and the
21、 release of the red photon is called thefluorescence lifetime. The fluorescence lifetime of the ruthe-nium complex is about 5 s. However, if oxygen is present, thefluorescence is quenched. This occurs when oxygen moleculescollide with the excited ruthenium molecules. During thecollision, energy is t
22、ransferred from the ruthenium to theoxygen, preventing emission. This process is called dynamicquenching, and it results in a decrease in the fluorescencelifetime proportional to the oxygen partial pressure. Thefluorescence lifetime will decrease from 5 s in an oxygen freeenvironment (for example, n
23、itrogen) to 1 s in ambient air (seeFig. 1). The most important aspect of using quenching foroxygen detection is that neither the oxygen nor the sensor isconsumed during a measurement.5. Interferences5.1 The presence of certain interfering substances in theheadspace may, in theory, give rise to incor
24、rect readings.Normal headspaces in empty or filled packages have not beenfound to be problematic. Relative humidity in that headspacealso has shown to not cause interferences.5.2 The temperature of the package, when tested, needs tobe measured.5.3 It is recommended that calibration, described below,
25、 ofthe chemically treated dots be conducted on packages contain-ing known oxygen concentrations as close to the level to beexperienced in actual tests. If the calibration is carried out atlevels far different than actual levels, the results may shownless precision than predicted in the precision and
26、 bias statementbelow.6. Apparatus6.1 Chemically Treated Components (aka “dots”) Coatedsubstrates of glass or flexible clear plastic have been found tobe satisfactory. A fluorescent dye polymer is deposited on oneside of the substrate.6.2 Adhesive is used to attach the non-coated side of the dotto th
27、e inside of the package. Silicone rubber adhesive has beenshown to be satisfactory. Other adhesives and double-sidedtape will work as well. No adhesive has yet been identifiedwhich interferes with the fluorescence of the dye as long as theadhesive is sufficiently translucent.NOTE 1The fluorescent li
28、fetime lies between 1 s and 5 s.FIG. 1 Relative Fluorescence Signals (I/I0) after Illumination of a Short Blue Pulse, Quenched by Different Oxygen Pressures in Air of20CF2714 08 (2013)26.3 Light Source producing sufficient energy in the appro-priate wavelength to activate the fluorescent dye. The li
29、ghtenergy is pulsed to allow determination of the decay rate.6.4 Light Detector with associated electronics, which is ableto determine the decay time of the fluorescence.6.5 Computer System to compare the measured fluorescentdecay rate of packages under test to packages containingknown oxygen concen
30、trations and present the results as oxygenconcentration.7. Reagents and Materials7.1 The coating used is described in Section 4. Othercomplexes may be used but their ability to measure oxygenmust be demonstrated.8. Precautions8.1 Temperature and relative humidity are critical param-eters affecting t
31、he measurement of oxygen permeation. If thisheadspace technique is to be used to calculate the oxygentransmission rate of packages, careful temperature and relativehumidity control can help to minimize variations due toenvironmental fluctuations. The average conditions and rangeof conditions experie
32、nced during the test period shall both bereported.8.2 Temperature of the chemically coated dot has an effecton the observed decay rate. Care must be taken to ensure thatthe dots temperature is known and controlled to 60.1C at thetime that the measurement is made.9. Sampling9.1 A statement as to the
33、number of samples to be tested isbeyond the scope of this test method.10. Test Specimens10.1 The test specimens can take many forms and includeany sealed package which contains a headspace containing agas or liquid.10.2 The test specimen must be sufficiently translucent toallow the coated dot to be
34、accessed. Alternatively, a windowcan be added to the package to allow access, but the design ofsuch window is beyond the scope of this test method.11. Conditioning11.1 No conditioning is normally necessary except the needto maintain temperature control of the samples as discussedelsewhere in this te
35、st method.12. Procedure12.1 CalibrationPrior to testing, the fluorescent dots andthe complete measuring system are to be calibrated.12.1.1 Fluorescent dots are affixed to the inside of a rigidpackage, flexible package, or a calibration fixture using adhe-sives described above. The package or fixture
36、 is sealed andflushed thoroughly with gases containing certified levels ofoxygen above and below the expected level of the packages tobe tested. As the package is flushed through a small opening, itis monitored for indicated oxygen level. When the level doesnot change for 1 min and the package or fi
37、xture has received atleast 20 times the headspace volume in flushing gas, thereading can be considered final and the reading entered into thecomputer based on the manufacturers instructions.12.1.2 The instrument manufacturers instructions are fol-lowed to test a calibration gas containing below the
38、oxygenlevel to be tested. Normally, this would be nitrogen, certified tocontain no oxygen. The value is entered as instructed.12.1.3 The instrument manufacturers instructions are fol-lowed to test a calibration gas containing above the oxygenlevel to be tested. Normally, this would be nitrogen conta
39、ininga certified level of oxygen no higher than 3 times the expectedlevel of oxygen in the package to be tested; that is, if thepackage to be tested is expected to contain 2 % oxygen, then acalibration gas of 6 % would be acceptable.12.1.4 Calibration using the calibration factors supplied bythe ins
40、trument manufacturer can be satisfactory, but care mustbe taken to ensure that the dots have been calibration in theoxygen concentration range of interest as discussed above.12.2 TestingA previously prepared, sealed, and flushedpackage of unknown oxygen concentration is measured by atest system cali
41、brated as described above.12.2.1 Dots that have been affixed within the package ofunknown oxygen concentration are exposed to the calibrated,fluorescent system in accordance with the manufacturersinstructions.12.2.2 The value indicated by the instrument is noted. Thevalue indicated can be expressed
42、in percent oxygen, partialpressure oxygen, or ppm oxygen.12.2.3 The environment of the dots can be the gaseousheadspace of the package or within a liquid depending on thetest design and the information sought.13. Calculation13.1 The computer system will do the calibration for theuser using the Stern
43、-Volmer equations to convert the decaytime into partial pressure of oxygen. The equations use thepreviously determined response of the system to the calibrationgases employed above.13.2 The red fluorescent signal has a certain delay in riseand decay depending on the oxygen partial pressure (pO2).Thi
44、s effect is shown in figure below. The typical fluorescentlifetime varies between 1 s in ambient air (pO2= 212 mbarat sea level) and 5 s in zero oxygen.13.3 From the signal the fluorescence lifetime can bederived. The mono-exponential fluorescence decay can bedescribed by:II05 expS2tD(1)where:I = fl
45、uorescence intensity at a certain time,I0= fluorescence intensity at the start of the decay (in thiscase on t = 1 s),t = time in s, and = fluorescence lifetime or time constant (TC).F2714 08 (2013)313.4 The software calculates the time constant from amono-exponential least squares fit of the fluores
46、cence signalsgenerated by the ruthenium in the coated dot, and from the timeconstant the oxygen concentration is calculated. The relation-ship between the oxygen partial pressure and the measuredfluorescence lifetime (time constant) is given by the Stern-Volmer Equation:05 11KSVpO2(2)where: = time c
47、onstant at current oxygen concentration,0= time constant in the absence of oxygen,KSV= Stern-Volmer constant, andpO2= oxygen partial pressure.13.5 This linear Stern-Volmer equation is transposed in thesoftware by Eq 3:1TC5 ApO21B (3)where:TC = time constant at current oxygen concentration in s (in S
48、tern-Volmer equation),pO2= oxygen partial pressure in mbar,A = slope of the Stern-Volmer line, andB = intercept of the Stern-Volmer line.13.6 The calibration process determines the slope and inter-cept (dA and dB) of the Stern-Volmer line for a low and a highoxygen concentration.14. Report14.1 The o
49、xygen concentration (expressed as percent, par-tial pressure or parts per million) is reported for each sampletested.14.2 The environment in which the test was conducted.14.3 The lot number of the dots used and the calibrationfactors are reported.15. Precision and Bias15.1 An interlaboratory study was conducted with 6 labo-ratories participating. Seven samples were prepared at each ofthree levels of oxygen concentration (approximately 0.04, 1.02,and 5.05 % oxygen). Each lab tested each sample three times.The repeatability and reproducibility
