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Liquid Scintillation Counting

Liquid scintillation counting (LSC)

Liquid scintillation counting theory


Liquid scintillation counting (LSC) is the standard laboratory method to quantify the radioactivity of low energy radioisotopes, mostly beta-emitting and alpha-emitting isotopes. The sensitive LSC detection method requires specific cocktails to absorb the energy into detectable light pulses. In order to efficiently transfer the emitted energy into light, LSC cocktails must consist of two basic components:

  • The aromatic, organic solvent
  • The scintillator(s) or fluors

As the majority of samples applied in LSC are aqueous-based, most of the LSC cocktails consist of:

  • The aromatic, organic solvent
  • The scintillator(s) or fluors
  • The surfactants

Principle of LSC
After excitation of the aromatic solvent molecules through the energy released from a radioactive decay, the energy is next transferred to the scintillator (also sometimes referred to as the "phosphor" or "fluor"). The energy absorbed through the scintillators produces excited states of the electrons, which decay to the ground state and produce a light pulse characteristic for the scintillator. The light is detected by the photomultiplier tube (PMT) of the liquid scintillation counter.

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LSC counting principle

Below is a schematic overview of the scintillation process.

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Liquid scintillation counting

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Liquid scintillation cocktails


A variety of scintillation cocktails is available to optimize the counting of almost any specific sample. When the sample is purely organic, it can be mixed with a lipophilic cocktail. When the sample is aqueous, or contains even a small proportion of water, then it needs to be mixed with an emulsifying cocktail. Scintillation counting can also be performed using a solid scintillator (for example, MeltiLex® for filtermats). The Scintillation cocktail brochure are helpful tools to choose a scintillation cocktail adapted to your particular application.

Liquid scintillation cocktails

Solid scintillant alternative (MeltiLex)


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Sample preparation


View detailed information on how to prepare various sample types for liquid scintillation counting.

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Quench


Read more about quenching and quench correction. Quenching occurs when the energy emitted by a radioisotope is not transferred completely into light and therefore is not detected by the PMT of the counting instrument. The decrease in final signal, as a result of quenching, can occur at various steps of the energy transfer process:

For example:

  1. The radioisotope can be physically separated from the solution in which the scintillator is dissolved. Properly homogenizing the solution will avoid physical quench.
  2. The beta particle can be absorbed by so-called quenching agents which will not re-emit the energy, blocking the scintillation process at that stage (the energy of the beta particle will not reach the scintillator, and no light will consequently reach the detector).
  3. The energy transmission could occur correctly, but once the light is emitted by the scintillator, it may be partially blocked by color quenching. As a consequence, the signal detected at the photomultiplier tube will not represent the total quantity of light truly emitted.

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Liquid scintillation vials and plates


Liquid scintillation counting usually requires homogeneous mixing between sample and scintillation cocktail to ensure ultimate contact between analytes and solutes. Good mixing is needed in vials as well as microtiter plates. Many plates and vials exist, and the choice of what type of vial or plate to use will depend on factors such as volume, chemical resistance, safety, and performance in combination with the cocktail of choice. You can view our Vials for Liquid Scintillation Counting and Microplate products to choose a vial or plate adapted to your application.

Glass Vials

Glass provides unparalleled optical clarity (good visibility) and is chemically inert, making it suitable for use with aggressive reagents and solvents. However, glass vials can break when falling on the ground, increasing the risk of contamination.

Borosilicate (Pyrex) glass is preferred due to its lower content of potassium, as compared with soda-glass. Potassium-40 is the largest contributor to background in glass vials. A maximum volume of 20 mL is fixed due to the dimensions of current photomultiplier tubes (2 inch diameter).

Product NumberDescriptionNominal VolumeCaps
6000167Pico Glass Vial7.0 mLFoil-lined urea screw caps
6000096Econo Glass Vial20.0 mLFoil-lined urea screw caps
6000097Econo Glass Vial20.0 mLPoly screw caps
6000128/6000129/6000349High Performance Glass Vial20.0 mLFoil-lined urea screw caps
6000134High Performance Glass Vial20.0 mLPoly-cone lined urea screw caps
6001009Oximate Vial20.0 mLFoil-lined urea screw caps

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Glass vials for scintillation counting


Plastic Vials

Plastic exhibits lower background levels than glass, but be aware of static electricity. For this reason, anti-static vials are available. Plastic is combustible and therefore easier for waste disposal. In addition, it is shatterproof. Plastic (polyethylene) is produced from fossil petrochemicals and therefore is preferred because these raw materials contain minimal measurable background.

Product NumberDescriptionNominal VolumeCaps
1200-421Polypropylene vial for MicroBeta4 mLPush on twist off cap
6000252/6000253Pico Pro Vial4.0 mLPush on stay on caps (LDPE)
6000292/6000293/6000592Pony Vial5.5 mLPush on twist off caps
6000192/6000193Pico Prias Vial6.0 mLPoly screw caps
6000186/6000187Pico Hang-in Vial6.0 mLHang-In poly screw caps
6000288/6000289Midi-Vial8.0 mLPush on twist off caps (Polypropylene)
6000480/6000488Hinge Cap Vial8.0 mLAttached caps
6000201Maxi-Vial18.0 mLPoly screw caps
6001095Oximate Vial20.0 mLFoil-lined urea screw caps
6001087/6001088Super Polyethylene Vial with glass vial thread20.0 mLFoil-lined urea screw caps
6000375/6001075/6008117/6008118Super Polyethylene Vial with quick closure20.0 mLPoly screw caps
6000477Low Diffusion Polyethylene Vial20.0 mLFoil-lined urea screw caps

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Plastic vials for LSC


Microplates

Scintillation results in the emission of light. In order to gain the best sensitivity, it is recommended to count plate-based assays in white microplates.

If your detection instrument reads from the top of the plate (such as a TopCount), one can use:

If the plates are read from the bottom, such as on a MicroBeta, the plate should have a clear bottom1:

1: Clear-bottom plates can be turned into opaque plates for top-reading by adding white adhesive BackSeal to the bottom of the plate.
2: Scintillant-embedded plates are designed for homogeneous (no-wash) assays. No liquid scintillation cocktail is required, as scintillant is already embedded in the walls of the microplate. In assays using scintillation-embedded plates, separation of "positive" and "negative" signal from the radiochemical is achieved by designing the assay in such a way that the radiochemical is associated with the walls or base of the microplate (and therefore able to interact with the scintillant) under given conditions. For example, in a cell-based uptake assay, radiochemical can only generate signal when taken up by the adherent cells, which are adhered to the base of the plate.
3: Filterplates are designed for filtration assays.

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Instrumentation


Vial Counters

Tri-Carb® Series

Tri-Carb Liquid Scintillation Counters are beta counters, and count sample vials with volumes from 4 mL up to 20 mL. They can discriminate between alpha- and beta- radiations, and also allow luminescence measurements.


QUANTULUS ®

The QUANTULUS Liquid Scintillation Spectrometer is a beta counter dedicated to ultra low level counting: the thicker shield eliminates effects of cosmic radiations and consequently reduces background. This makes the QUANTULUS Liquid Scintillation Spectrometer a good choice for Carbon-14-dating.


Flow Scintillation Analyzers

Radiometric flow scintillation analyzers (FSA) monitor single or dual radiolabeled samples separated by HPLC.


Plate Counters

In addition to standard protocols using vial counters, radiometric assays can also be performed using higher-throughput detectors:


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TopCount

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The liquid scintillation counting technique can be applied to hundreds of radiometric applications, and each will require a scintillation cocktail. Almost all cocktails will give counting results with any application, but the quality and reproducibility of the data will depend on the choice of the cocktail as well as on the sample composition, volume, temperature, and counting device.

The Scintillation Cocktails and Consumables brochure.

PerkinElmer Technical Support offers you the expertise you need to confirm your choice or can recommend the best cocktail for a particular application.

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