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LS 6000 Scintillation System User’s Manual
PN 247971-F
7-1
How Sample Preparation Affects Results
Chemiluminescence
7
7
How Sample Preparation Affects Results
This chapter discusses several factors that can interfere with accurate results:
chemiluminescence, statics, two-phase separation, and counting solid samples such as filters.
7.1 Chemiluminescence
Introduction
Investigators who work with liquid scintillation instruments have long been plagued by a
problem that occurs with certain types of scintillation mixtures in which light-producing
events take place that are not the result of radioactivity of the sample. The light-producing
events in question may be caused by one of several types of reactions - photoluminescence,
chemiluminescence, or bioluminescence.
These sources of light all have in common the fact that they produce only one photon per
event—hence the common term “single photon events” to describe them.
This phenomenon becomes significant because of the “coincident detection” method used in
LS counting. The sample being counted is monitored simultaneously by two photomultiplier
tubes, and only those events observed by both tubes are counted. The two tubes must each
observe an event within some very brief “resolving time”, for the event to be considered
coincident, and included in the count. Typical resolving times are on the order of 20 X 1O~
sec. Since one “singles” event releases only one photon, it cannot be observed by both tubes
simultaneously, and therefore will not be counted.
However, with a sample in which a large number of singles events occur, the probability
increases that the two tubes will each observe two different singles events at approximately
the same instant, thus producing a count. This type of “random coincidence event” can be
significant enough to produce erroneous cpm.
Lum-Ex Correction provides a means of determining when the results of counting are being
distorted by random coincidence events.
Sources of Single Photon Events
Some very common sample preparations can cause so many single photon events that
hundreds of thousands of these photons are coincident and look like real cpm.
Some of these sample conditions are:
1. Samples with an alkaline pH.
2. Samples with peroxides (either organic peroxides or hydrogen peroxide used for
dissolving polyacrylamide gels or bleaching hemoglobin). Peroxides with alkaline
solutions cause particularly severe chemilumlnescence.
3. Use of tissue solubilizers, especially with emulsifier cocktails. Tissue solubilizers are
designed for use with nonaqueous cock-tails.
4. Samples, cocktails or vials exposed to sunlight or UV light from sterilization lamps or
UV lamps for detecting fluorescent molecules.
- LS 6000 Series 1
- Table of Contents 3
- Introduction 11
- Principles of Operation 12
- Operating the Instrument 12
- Operating Modes 13
- 1.3 Specifications 14
- Precautions and Limitations 15
- Figure 1.1 Standard Vial 15
- Miniature Vials 16
- 1.5 Hazards 17
- Maintenance 18
- Getting Started 19
- 2.2 Power Failure 21
- 2.3 Operating Controls 21
- Operator Control Key pad 22
- Using the Operating Controls 24
- 2.4 Using the Racks 25
- Using the Racks 26
- Setting Up the Racks 27
- 2.5 Preparing the Printer 29
- 2.6 System Setup 30
- Energy Scale 31
- Printer Paging 32
- Allow Interrupt Count 32
- System Setup 33
- Figure 2.9 RS232 Setup Menu 33
- Date/Time 35
- Auto DPM 35
- 2.7 Calibration 36
- Counting Samples 39
- Starting the Automatic Count 40
- Conducting Count Single Rack 41
- 3.4 Auto DPM 46
- 3.5 Multi-Task 47
- Interrupt Count in Multi-Task 48
- Multi-Task 50
- Interrupt Data 51
- Setting Up User Programs 59
- 4.2 Editing A User Program 61
- Editing A User Program 62
- Comments 65
- Counting Time 65
- Liquid or Xtal Scintillator 65
- Isotope 1 65
- Isotope 2 and Isotope 3 66
- Edit Other Parameters 67
- Counting Precision 69
- Background/Blank Subtraction 69
- Lum-Ex Correction 71
- Phase Monitor 72
- Low Level 72
- Low Count Reject 72
- Output Formats 72
- Count Data 75
- Raw Data 75
- Collecting Spectral Data 76
- 4.3 Copy User Program 77
- Copy User Program 78
- 5.2 CPM/Xtal CPM 80
- CPM/Xtal CPM 81
- Results for CPM/Xtal CPM 83
- 5.4 Auto DPM 85
- Setting Up Auto DPM 86
- Loading Samples for Auto DPM 86
- Results for Auto DPM 86
- Setting Up DPM 87
- 5.6 Xtal DPM 89
- Xtal DPM 90
- Setting Up Xtal DPM 91
- Loading Samples for Xtal DPM 92
- 5.7 DPM % of Reference 93
- Setting Up DPM % of Reference 94
- Xtal SL DPM % of Reference 95
- 5.9 Single Photon Monitoring 98
- Data Calculation 100
- Single Photon Monitoring 100
- Isotope/DPM Libraries 103
- Accessing the Isotope Library 104
- Printing the Isotope Library 104
- The Isotope Library 105
- Setup Menu 106
- PN 247971-F 108
- 5 minutes 109
- 6.2 Setting Up A Quench Curve 110
- Setting Up A Quench Curve 112
- Counting the Standards 114
- Editing Quench Curves 120
- Deleting A Quench Curve 124
- Manual Entry of Quench Curves 125
- 7.1 Chemiluminescence 127
- Interpretation of Results 128
- Reducing Single Photon Events 128
- 7.3 Two Phase Samples 129
- Procedures 131
- Analysis of Data 131
- H Counting Efficiency 132
- C Counting Efficiency 132
- Background 133
- Contamination 133
- Instrument Specifications 135
- Temperature Control Accessory 138
- Installation Requirements 139
- Electrical Requirements 140
- 0.5 to 1.0 m in 140
- Environment Requirements 142
- . Note that the output 144
- Datum IDs 146
- CHAPTER 1, PART 31 167
- Region I 170
- Region II 170
- Region III 170
- Region IV 170
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