1、Designation: F 2714 08Standard Test Method forOxygen Headspace Analysis of Packages Using FluorescentDecay1This standard is issued under the fixed designation F 2714; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 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 sealedpackage w
3、ithout 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 the package surf
4、acewithout 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 asstandard. No ot
5、her 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 applica-bility
6、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 fillingoperation.2.3 A pul
7、sing 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 content of the
8、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 package under test is
9、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:3.3.1 Package Pe
10、rmeability 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 (ml) of oxygen. Th
11、e 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 leakcan be suspected
12、. 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.1This test method is under the jurisdiction of ASTM Co
13、mmittee F02 on FlexibleBarrier Packaging and is the direct responsibility of Subcommittee F02.40 onPackage Integrity Test Methods.Current edition approved Aug. 1, 2008. Published August 2008.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United S
14、tates.3.3.3 Effcacy of the MAP Packaging ProcessIftheheadspace oxygen concentration is found to be higher thanexpected soon after packaging, the gas flushing process maynot be working as well as expected. Various techniques canevaluate whether the MAP system is functioning properly.3.3.4 Storage Stu
15、diesAs the method is non-destructive,the headspace can be monitored over time on individualsamples to insure that results of storage studies such as shelflife testing are correctly interpreted.4. Discussion4.1 Oxygen sensing based on fluorescence is well estab-lished. The typical indicators used are
16、 ruthenium complexesand porphyrins both of which are compatible with lightemitting diodes (LEDs). In one oxygen sensitive coating, tris(4,7 biphenyl 1,10 phenanthroline) ruthenium chloride is useddue to its stability, long lifetime, and strong absorption between400 nm and 500 nm in the blue region o
17、f 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 and is detected by aphotomultiplier tube or a photo detector to offer the flexibilityof a large dynamic range and fast response
18、 time. The rutheniumcomplex is immobilized in a highly chemically resistantsubstrate.4.2 The principle of fluorescence quenching is based on theexcited state characteristics of a specific dye. Dynamic quench-ing is the transfer of energy from a fluorescent dye in itsexcited state to oxygen in the su
19、rrounding 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 The ruthenium complex is excited with blue light froman LED. Short pulses of blue light from the LED are absorbedby the rutheni
20、um 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 release of the red photon is called thefluorescence lifetime. The fluorescence lifetime of the ruthe-nium complex is about 5
21、s. However, if oxygen is present, thefluorescence is quenched. This occurs when oxygen moleculescollide with the excited ruthenium molecules. During thecollision, energy is transferred from the ruthenium to theoxygen, preventing emission. This process is called dynamicquenching, and it results in a
22、decrease in the fluorescencelifetime proportional to the oxygen partial pressure. Thefluorescence lifetime will decrease from 5 s in an oxygen freeenvironment (for example, nitrogen) to 1 s in ambient air (seeFig. 1). The most important aspect of using quenching foroxygen detection is that neither t
23、he 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 incorrect readings.Normal headspaces in empty or filled packages have not beenfound to be problematic. Relative humidity in that he
24、adspacealso 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, ofthe chemically treated dots be conducted on packages contain-ing known oxygen concentrations as close to the level to beexp
25、erienced 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 bias statementbelow.NOTEThe fluorescent lifetime lies between 1 s and 5 s.FIG. 1 Relative Fluorescence Signals (I/I0) after I
26、llumination of a Short Blue Pulse, Quenched by Different Oxygen Pressures in Air of20CF27140826. 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 subs
27、trate.6.2 Adhesive is used to attach the non-coated side of the dotto the 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
28、long as theadhesive is sufficiently translucent.6.3 Light Source producing sufficient energy in the appro-priate wavelength to activate the fluorescent dye. The lightenergy is pulsed to allow determination of the decay rate.6.4 Light Detector with associated electronics, which is ableto determine th
29、e decay time of the fluorescence.6.5 Computer System to compare the measured fluorescentdecay rate of packages under test to packages containingknown oxygen concentrations and present the results as oxygenconcentration.7. Reagents and Materials7.1 The coating used is described in Section 4. Othercom
30、plexes may be used but their ability to measure oxygenmust be demonstrated.8. Precautions8.1 Temperature and relative humidity are critical param-eters affecting the measurement of oxygen permeation. If thisheadspace technique is to be used to calculate the oxygentransmission rate of packages, caref
31、ul temperature and relativehumidity control can help to minimize variations due toenvironmental fluctuations. The average conditions and rangeof conditions experienced during the test period shall both bereported.8.2 Temperature of the chemically coated dot has an effecton the observed decay rate. C
32、are 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 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 i
33、ncludeany 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 accessed. Alternatively, a windowcan be added to the package to allow access, but the design ofsuch window is beyond the scope of this te
34、st method.11. Conditioning11.1 No conditioning is normally necessary except the needto maintain temperature control of the samples as discussedelsewhere in this test method.12. Procedure12.1 CalibrationPrior to testing, the fluorescent dots andthe complete measuring system are to be calibrated.12.1.
35、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 is sealed andflushed thoroughly with gases containing certified levels ofoxygen above and below the expected level of the packages tobe
36、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 fixture has received atleast 20 times the headspace volume in flushing gas, thereading can be considered final and the reading entered into
37、 thecomputer based on the manufacturers instructions.12.1.2 The instrument manufacturers instructions are fol-lowed to test a calibration gas containing below the oxygenlevel to be tested. Normally, this would be nitrogen, certified tocontain no oxygen. The value is entered as instructed.12.1.3 The
38、instrument manufacturers instructions are fol-lowed to test a calibration gas containing above the oxygenlevel to be tested. Normally, this would be nitrogen containinga certified level of oxygen no higher than 3 times the expectedlevel of oxygen in the package to be tested; that is, if thepackage t
39、o 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 instrument manufacturer can be satisfactory, but care mustbe taken to ensure that the dots have been calibration in theoxygen concentration
40、range of interest as discussed above.12.2 TestingA previously prepared, sealed, and flushedpackage of unknown oxygen concentration is measured by atest system calibrated as described above.12.2.1 Dots that have been affixed within the package ofunknown oxygen concentration are exposed to the calibra
41、ted,fluorescent system in accordance with the manufacturersinstructions.12.2.2 The value indicated by the instrument is noted. Thevalue indicated can be expressed in percent oxygen, partialpressure oxygen, or ppm oxygen.12.2.3 The environment of the dots can be the gaseousheadspace of the package or
42、 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-Volmer equations to convert the decaytime into partial pressure of oxygen. The equations use thepreviously determined response of the sy
43、stem 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).This effect is shown in figure below. The typical fluorescentlifetime t varies between 1 s in ambient air (pO2= 212 mbarat sea level) and 5
44、s in zero oxygen.13.3 From the signal the fluorescence lifetime can bederived. The mono-exponential fluorescence decay can bedescribed by:F2714083II05 expSttD(1)where:I = fluorescence intensity at a certain time,I0= fluorescence intensity at the start of the decay (in thiscase on t = 1 s),t = time i
45、n s, andt = fluorescence lifetime or time constant (TC).13.4 The software calculates the time constant t from amono-exponential least squares fit of the fluorescence signalsgenerated by the ruthenium in the coated dot, and from the timeconstant the oxygen concentration is calculated. The relation-sh
46、ip between the oxygen partial pressure and the measuredfluorescence lifetime (time constant) is given by the Stern-Volmer Equation:t0t5 1 1 KSV pO2(2)where:t = time constant at current oxygen concentration,t0= time constant in the absence of oxygen,KSV= Stern-Volmer constant, andpO2= oxygen partial
47、pressure.13.5 This linear Stern-Volmer equation is transposed in thesoftware by Eq 3:1TC5 A pO21 B (3)where:TC = time constant at current oxygen concentration in s(t in Stern-Volmer equation),pO2= oxygen partial pressure in mbar,A = slope of the Stern-Volmer line, andB = intercept of the Stern-Volme
48、r 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 oxygen concentration (expressed as percent, par-tial pressure or parts per million) is reported for each sampletested.14.2 The envi
49、ronment 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 was computed for eachsample. The results were similar enough at each level to permitpooling the repeatability and reproducibility standard devi
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