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LS 6000 Scintillation System User’s Manual
PN 247971-F
7-4
How Sample Preparation Affects Results
Counting Filters And Precipitates
This phase problem can often be eliminated by using less sample, more cocktail, or switching
to a cocktail with better sample holding characteristics. Sometimes diluting the sample with
water or neutralizing the pH will work.
If you are not sure whether your sample is separating into two phases, a simple test can be
done. Prepare a glass vial of the cocktail and sample you use for the experiment. Observe the
sample over the time and temperature range it is exposed to during counting. If the sample
stays single phase, there is no problem. If it becomes
two phase, try some of the procedures
outlined above on fresh preparations. The 2 Phase Monitor (if installed) flags any samples
detected as two phase.
7.4 Counting Filters And Precipitates
Any sample that is not intimately mixed with the cocktail will count with a low efficiency and
with unpredictable and varying results. Quench monitors are not accurate, DPM are difficult
to calculate, and even comparisons of CPM between samples may give misleading results.
Counting precipitates on filters or as pellets from centrifugation is a very common procedure.
It can be used effectively if certain precautions are taken. There are two main problems in
getting accurate and reproducible results from filters or precipitates. First, the amount of
physical precipitate will affect the CPM recorded. More sample material will absorb more of
the radio-active decay events. This beta absorption results in decreased CPM with increasing
amount of precipitate. The second problem results from the precipitate dissolving in the
cocktail over a period of time. This results in variability between repeat counts and between
different samples.
There are two ways to avoid these problems. The less desirable method is to have samples
with approximately the same amount of precipitate and to select a cocktail in which the
precipitate will not dissolve. While DPM cannot be calculated for these samples, at least the
CPM between samples can be compared.
The other, and better, method is to dissolve the sample completely before counting. In the
case of proteins or nucleic acid precipitates, this is a very simple procedure. Add enough 0.05
to 0.1 M KQH (100 µL is a good starting volume) to wet the filter or dissolve the pellet. After
mixing, add a cocktail such as Beckman Ready-Solv HP. This will emulsify the KOH along
with the sample. It is not necessary for the filter to dissolve. This
type of preparation is not
affected by the amount of precipitate, and DPM calculations are easily done in the usual
manner.
7.5 Distinguishing Sample And Instrument Variability
Introduction
The sample preparation problems discussed in this chapter can lead to counts that are too
high, too low, that increase with time, decrease with time, or go up and down in a random
pattern. This is often mistaken for instrument malfunction. However, there are instrument
problems that can cause similar symptoms. This section outlines how sample problems and
instrument problems can be distinguished. These tests are not 100% conclusive but they do
form good grounds for you to analyze the most common problems encountered and to
communicate valuable information to the service representative.
- 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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