PRESENTATION ON lsc

PRESENTATION ON : 

LIQUID SCINTILLATION SPECTROMETRY Submitted by Submitted To: Kalyani Patel Dr . Prateek Jain M.Pharm (1 st sem ) PRESENTATION ON

INTRODUCTION: 

LIQUID SCINTILLATION SPECTROMETRY- Liquid scintillation spectrometry is a high efficiency laboratory counting system. This system used for the detection and quantification of radiation even with very low penetrating power such as beta particles. It has wide range applications in Biology, Medicine and Environmental studies INTRODUCTION

FUNDAMENTALS OF LIQUID SCINTILLATION SPECTROMETRY: 

Radioactive emission Scintillators Solvents FUNDAMENTALS OF LIQUID SCINTILLATION SPECTROMETRY

Radiactive emission: 

Radioactive decay occurs with the emission of particles or electromagnetic radiation from an atom due to a change within its nucleus. Forms of radioactive emission include: alpha particles ( α), beta particles ( β), and gamma rays (γ). Liquid scintillation counting has its primary application the counting of weak beta emitters, such as tritium, carbon-14, phosphorus-32 Radiactive emission

Scintillators : 

Scintillators are a group of molecules responsible for conversion of the energized solvent molecule to the light. Scince this process is essentially fluorescence, the scintillators are usually aromatic molecules that are highly conjugated. The primary scintillators should have following properties: The primary scintillators should exhibit a high efficiency of light emission when activated by the radiation. Not only this process be efficient but the wavelength of the light must be in the region of high sensitivity of the PMT The light flouresced be above 350nm. This allows for the use of glass optics and sample containers, whereas light of shorter waveength would require quartz or fused silica sample containers and optics. 2,5-Diphenyloxazole (PPO) is one of the most commonly used primary scintillator . The flourescence emission maximum of this compound is 363nm in toluene. PPO has excillent solubility in the usual scintillatior solvent. Scintillators

Primary scintillators: 

Primary scintillators

Secondary scintillatores : 

Secondary scintillators sometimes it is desirable to add scintillators to the counting solution in order to get a sufficient yield, called the secondary flour which absorbs light emitted by the primary scintillators and reemits at a higher wavelength. It is present in concentration of about 1/10 to the primary scintillator . They should be use only when of the following condition is met: The PMT tube of the counter has a more efficient response at a higher wavelength. The sample contains a compound that quenches the primary scintillator . 2,2-p-phenylenebis(5-phenyloxazole) orPOPOP is the most commonly used secondary scintillator . It is used at concentration typically around 0.5g per litre of toluene and has a flourescence maximum at 415nm. The greaterconjugation of double bonds in POPOP causes the its flourescence maxima to be at higher wavelengths. Primary and secondary scintillators are often combined in toluene to form a “counting coctail ”. Secondary scintillatores

Secondary scintillators : 

Secondary scintillators

Solvent : 

The solvent should have- A high solubility for scintillators . Scince most scintillators are water insoluble organic molecules , the solvent should be relatively non polar. The energy transfer from the beta particle to the solvent should be efficient. The ideal solvent should be transparent to the photons emitted from the scintillators . They have ability to solubilize the sample. It should form a homogenous solution and not freeze at working tempretures . e,.g . toluene, xylene Solvent

SOLVENTS : 

SOLVENTS

Theory : 

In the liquid scintillation process, energy from particles emitted in the disintegration of the nucleus is translated through a series of energy transfer to the production of visible light. As the beta particles pass through an aromatic solvent , such as toluene or xylene a fraction of the solvent molecule becomes excited through the s and p electrons. The excited molecule transfer their energy to the dissolved scintillators . The excited molecules returns to the ground state by emitting photons in the wavelength ranges of u.v . or visible light. In the case of p- terphenyl (1), the wave length of the fluoresced light is 335 nm in the tolune . The scintillatin transfer processes can be summarized as- b + solvent = solvent* Solvent* +primary flour = solvent +primary flour* Primary flour*+ secondary flour= primary flour+ secondary flour* Secondary flour*= secondary flour+ hu Theory

Instrumentation : 

SINGLE TUBE LIQUID SCINTILLATION COUNTER :- In an idealized counting system consisting of p- terphenyl -POPOP-toluene solution. The disintegration of the radionucleoide causes the release of a beta particle . The energy of the beta particle is then absorbed by the flour solution which in turn is emits photons. The photon strike the photomultiplier tube to produce a descrete electrical pulse which is amplified and fed to the pulse height analyser . Once the pulse is accepted, it is passed on to the scaler , which sums the accepted pulses. To over come the difficulties caused by the thermal electrons, a two tube system is routinely used for liquid scintillatin counting. Instrumentation

Block diagram of single liquid scintillation counter:- : 

Block diagram of single liquid scintillation counter:-

TWO TUBE LIQUID SCINTILLATION COUNTER: 

Two tube liquid scintillation counter employs two photomultiplier tubes that simultaneously look at that sample. This type of instruments is based on the measurement of simultaneous events. The number of coincidence(simultaneous) pulses arising from random events which are passed by the coincidence circuit can be calculated by the following formula: T= 2N 1 N 2 (R) Where, T – no of coincidence pulses passed by per minute N 1 - thermal noise rate in cpm for photomultiplier1 N 2 - thermal noise rate in cpm for photomultiplier2 R- resolution time of the coincidence circuit, min TWO TUBE LIQUID SCINTILLATION COUNTER

BLOCK DIGRAM OF TWO TUBE LIQUID SCINTILLATION COUNTER: 

BLOCK DIGRAM OF TWO TUBE LIQUID SCINTILLATION COUNTER

Two tube liquid scintillation counter : 

Two tube liquid scintillation counter

THE FIGURE OF MERIT: 

The performance of a liquid scintillation counter is often expressed in terms of a “ figure of merit ” , which is an expression of the counter. THE FIGURE OF MERIT= S 2 /(S+2B) Where, S= total net sample count B= background counts In single –label counting a principle concern is to maximize the figure of merit when the activity of the sample is low. THE FIGURE OF MERIT

LIQUID SCINTILLATION PROCESS : 

LIQUID SCINTILLATION PROCESS

Problems associated with LSC: 

Sample prepration Variable quenching Sample preparation - sample prepration can bew a problem due to the requirement of having a clear (or at lest translucent) solution or dispersion in a non aqueous solvent such as toluene and dioxane . Many methods are used to overcome this problem ( e.g. use of detergents). Colour and chemical quenching chemical quenching:some of the energy released by the emission of the beta particle during radioactive decay is absorbed by the liquid component of the sample. Therefore, the total amount of released energy is unavailable for producing photons. colour quenching: coloured material in the sample absorbs a portion of the photons emitted by the scintillator . This type of quenching is common in samples that have been prepared using colored biological specimens such as blood or plant tissue extracts. Colour quenching, can be reduced or eliminated by the digestion with hydrogen peroxide and perchloric acid. Problems associated with LSC

Applications of Liquid Scintillation Spectrometry: 

Tracer for conventional analytical techniques In vitro studies Studies in isolated tissues Studies in whole animals Miscllaneous applications Applications of Liquid Scintillation Spectrometry

Tracer for conventional analytical techniques: 

a common method for establishing the recovery of complex isolation technique utilizes radiolabeled compounds . In this case the original sample is spiked with a small but well-known quality of radiolabeled analyte . After the sample has been carried through the analyte procedure, the amount of radioactivity in the final sample is determined. From these data and knowledge of the amount of radioactivity added initially, the recovery efficiency can be calculated. e.g (a) this method is used for the analysis of N- nitrosonornicotine (NNN) in tobacco and tobacco smoke. (b) it is also used to determine extraction efficiency for nefopam from plasma. Tracer for conventional analytical techniques

In vitro studies:-: 

radiolabeled drugs are very useful in determination of properties such as dissolution, partitioning between two phases and binding to other compounds. e. g. (a) dissolution of cholesterol in simulated bile has been monitored by liquid scintillation counting. Liquid scintillation counting can be used to determine the partition coefficient of compound between two immiscible phases. This is particularly usefull when partitioning is quite small and leads to very low solute concentrations in one phase. e.g. (b) the partition coefficient and rate of transfer from water into toluene containing didodecyl phosphate of 3 H-2-pyrrolidyl-methyl-N-methylcyclopentylphenylglycolate. Radiolabeled drug has been utilized in binding studies of various types. In vitro studies :-

Studies in isolated tissues:- liquid scintillation counting and radiolabeled drugs are used to study drug distribution and or metabolism in isolated tissue preparations.   : 

Studies in isolated tissues:- liquid scintillation counting and radiolabeled drugs are used to study drug distribution and or metabolism in isolated tissue preparations.

Studies in whole animals:- The administration of radiolabeled drugs to animals and humans has provided an important tool for the study of absorption, distribution, metabolism and excretion (ADME) drugs. : 

Studies in whole animals:- The administration of radiolabeled drugs to animals and humans has provided an important tool for the study of absorption, distribution, metabolism and excretion (ADME) drugs.

MISCELLANEOUS APPLICATIONS:- liquid scintillation counting can also be used in followings- : 

One of the most widely known application of L.S.C. of 14 C is in high precision dating of the rafiocarbon time scale for the purpose of calibration. The method has been applied in nuclear physics for neutron counting in the presence of gamma radiation. The use of liquid scintillation analysis in the monitoring of a- emmiting and transuranium nuclides in the environmental samples. MISCELLANEOUS APPLICATIONS:- liquid scintillation counting can also be used in followings-