Post on 10-Oct-2020
LSC Cocktails – Form & Function
LSC 2013, Barcelona, Spain
James Thomson
Meridian Biotechnologies Ltd.
How does an LSC cocktail work ? The majority of radioactive species are present in an aqueous form, and as
such are not miscible with aromatic solvents.
The presence of surfactants (detergents) in the cocktail enables an aqueous
sample to come into intimate contact with the aromatic solvent by forming a
stable microemulsion.
When the radioactive particle collides with the solvent molecule the process
below takes place and light is detected.
b hn
LSC Cocktail Beta particle Light
LSC Counter
The aromatic solvent is necessary since it contains a high
density of π electrons, necessary for the efficient transfer of
the energy of radioactive decay.
The surfactant is needed to enable a stable microemulsion to
be formed when aqueous samples are present, necessary for
stable conditions over the counting period.
The scintillators are present to emit a light pulse which is
within the optimum detection wavelength of the photomultiplier
tube.
Why are these components in an LSC
Cocktail?
Solvent
C
C
C C
C
C
H2
H2 H2
H2 H2
H2 Solvent (planar view)
LSC cocktail LSC cocktail with radioisotope
π electron cloud
What happens at the molecular level?
LSC cocktail with radioisotope LSC cocktail with sample present
Complete guarantee that any
radioactive particle will collide with
a solvent molecule
In this real world situation there is a
reduced chance of a radioactive
particle colliding with a solvent
molecule due to the presence of
the sample.
What happens when a sample is added?
History - Solvents
1950-1960 Benzene
(Toxic, flammable & carcinogenic)
Dioxane + Naphthalene
(Toxic, flammable & carcinogenic)
1960-1985 Toluene, Xylene & Pseudocumene
(Flammable & toxic)
1985-2013 Linear alkyl benzene (LAB)
(Flash point 135°C and Irritant)
Phenylxylylethane (PXE)
(Flash point 145°C and Irritant)
Di-isopropylnaphthalene (DIN)
(Flash point 145°C and Irritant)
History - Solvents
What were the driving forces behind the evolution?
• In 1974 the UK introduced the Health and Safety at Work Act
highlighting the toxicity issues surrounding the use of benzene and
substituted benzenes as solvents.
• Sadly the only change that occurred at first was to use xylene instead of
toluene.
• Further change to pseudocumene (1,2,4-trimethylbenzene).
• 1984 - first true “high flash point safer” cocktail emerges - Opti-Fluor.
Based on LAB (linear alkyl benzene) which has a flash point of ~135°C.
• LAB
o Precursor for dodecylbenzene sulphonate detergent (Soap powder)
o Readily available in large quantities
o High flash point
o Slightly lower 3H efficiency vs. Toluene
o Biodegradable when in combination with detergents.
History - Solvents
What were the driving forces behind the evolution?
• In 1985/6 DIN (di-isopropylnaphthalene) was “discovered”.
• Used as an alternative to PCB’s in transformer fluids and as the solvent
carrier in carbonless copy papers.
• Was found to be an excellent LSC solvent due to being highly aromatic.
o High flash point of ~145°C
o Readily available in large quantities as water white solvent
o Higher 3H efficiency vs. Toluene
o Biodegradable when in combination with detergents.
• At the same time PXE (phenylxylylethane) also “discovered”.
• Developed for use as a transformer fluid with a lower “thickening point”
and used on the Alaska pipeline.
o Similar properties to DIN v but slightly more viscous.
History - Solvents 1. Toluene
C7H8 [Flash Point 4°C]
CAS No. 108-88-3
RPH = 100
2. Xylene (mixed isomers)
C8H10 [Flash Point 27°C]
CAS No. 1330-20-7
RPH = 110
3. Pseudocumene (1,2,4-trimethylbenzene) C9H12 [Flash Point 49°C]
CAS No. 95-63-6
RPH = 112
CH3
CH3
CH3
CH 3
CH 3
CH 3
History - Solvents 4. Dodecyl Benzene (LAB -Linear Alkyl Benzene) C18H30 [Flash Point 145°C]
CAS No. 123-01-3
RPH = 94
5. Di-isopropylnaphthalene (DIN) C16H20 [Flash Point 147°C]
CAS No. 38640-62-9
RPH = 112
6. 1-Phenyl-1-Xylyl Ethane (PXE) C16H18 [Flash Point 147°C]
CAS No. 6196-95-8
RPH = 110
C12H25
C3H7
C3H7
CH3
CH3
C
CH3
H
History - Scintillators
Most of the work carried out in scintillator development was carried
out in the 1950’s and 1960’s with Hayes & Ott (1957) publishing a
definitive paper on oxazole scintillators.
The order of appearance of the other scintillators was as follows:-
PPO in 1957
PBD in 1958
Butyl-PBD in 1966
POPOP in about 1964
Dimethyl-POPOP in about 1966
bis-MSB in about 1966
History - Scintillators 1957-2013
Primary scintillators
PBD 2-Phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole
(Expensive synthesis / low solvent solubility)
Butyl-PBD 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole
(Expensive synthesis / better solvent solubility (8 x PBD) / CLM sensitive)
PPO 2,5-diphenyloxazole
(Affordable synthesis / excellent solubility / no CLM)
Secondary scintillators
POPOP 1,4-Bis(5-phenyl-2-oxazolyl)benzene
(Expensive synthesis / low solvent solubility)
Dimethyl-POPOP 1,4-Bis(4-methyl-5-phenyl-2-oxazolyl)benzene
(Expensive synthesis / low solvent solubility)
bis-MSB 1,4-Bis(2-methylstyryl)benzene
(Affordable synthesis / excellent solubility / no CLM)
History - Scintillators
A. 2,5-diphenyloxazole (PPO) (Primary Scintillator) C15H11NO λmax 370 nm
CAS No. 92-71-7
B. [2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole] (Butyl PBD) (Primary Scintillator) C24H22N2O λmax 364 nm CAS No. 15082-28-7
N
O
N
O
N
H3C
CH3
CH3
Primary scintillators
History - Scintillators
Secondary scintillators
C. 1,4-Bis(2-methylstyryl)benzene (bis-MSB) (Secondary Scintillator) C24H22
λmax 425 nm CAS No. 13280-61-0
D. 1,4-Bis(4-methyl-5phenyl-2oxazolyl)benzene (Dimethyl POPOP) (Secondary Scintillator) C26H20N2O2
λmax 427 nm CAS No. 3073-87-8
CH3
CH3
O
N N
O
H3C CH3
History - Detergents
1950-1960
Co-solvents + naphthalene
Triton X-100
1960-2013
Nonyl phenol ethoxylates (NPE’s)
Phosphate esters
Alkyl phosphates
Sulphosuccinates
Sarcosinates
Co-solvents
2006-??
Alcohol ethoxylates
History - Detergents
Nonyl phenol ethoxylates (NPE’s)
The first true microemulsion cocktail (~1955, Patterson & Green) was
based on Triton X-100 (Octyl phenol ethoxylate) and again, like solvents,
the detergent industry was the source.
Soon after that NPE’s became available and they are still being used
today in over 90% of all LSC cocktails.
They are the “building block” for microemulsion formation and the other
detergent additives simply enhance the microemulsion performance.
They are available in a variety of ethoxylate chain lengths but only a few
are used in LSC cocktails (usually EO=5 to EO=10).
Longer EO chain lengths work better at 20°C and above while the
shorter chain lengths are best suited to low temperatures.
The only performance drawback is that the NPE’s form gels and semi-
gels at >20% loading and therefore additives are needed to extend the
working range.
History - Detergents
Additives
To overcome the gel formation co-solvents are added and these are
usually long chain alcohols, typically diglycols.
Other additives such as sulphosuccinates are also good at extending the
capacity for water and dilute aqueous samples and sodium dioctyl
sulphosccinate is a commonly encountered component of LSC cocktails.
Higher strength (>0.5M) samples present a stability problem in that they
will break down the microemulsion and form what customers describe as
a “milky” solution. This can be overcome by using free-acid or
neutralized phosphate esters which have the ability to keep more
concentrated samples in a stable microemulsion. Such phosphate esters
can be derived from alcohols or even NPE’s.
History - Detergents
1. Ethoxylated Alkylphenols (Non-Ionic detergent)
CAS No. 9016-45-9
2. Mono-/Di- phosphate ester (Anionic detergent)
CAS No. 298-07-7
3. Sodium di-octylsulphosuccinate (Anionic detergent)
CAS No. 577-11-7
C9H19 (OCH2CH2)nOH
P OH
O
RO
OH OH
RO
O
ORPand
O
O
O
O
C 8 H 17
C 8 H 17
O
O
S
O
Na
Where are we today? >90 % of all currently available LSC cocktails are based on NPE’s
They work very well.
Not all NPE’s will continue to be available.
Some of these cocktails are sold as “biodegradable”.
NPE’s are not readily or fully biodegraded and produce metabolites that
are known endocrine disrupters.
EEC directive 2003/53/EC came into force in 2003 and put in place
controls to restrict the marketing and use of nonyl phenol (NP) and
NPE’s. Similar restriction in force in Canada and now being considered
in Japan & the USA.
Cocktail waste containing NPE’s cannot be drain disposed
in either the EU or Canada.
NPE’s – What is the problem?
Alkyl phenol ethoxylates generally end up at sewage treatment plants,
where unfortunately they are only partially degraded and then enter rivers
and the sea in the treated sewage.
When alkyl phenol ethoxylates break down in sewage treatment or a river
they produce three main groups of alkylphenolic compounds:
• Alkyl phenol ethoxylates with fewer ethoxylate groups
• Alkylphenoxy carboxylic acids
• Alkyl phenols
Where are we today?
NPE’s - Hormone disrupting effects
Research indicates that NPE metabolites disrupt the endocrine system and
interfere with the hormones of fish and shellfish.
Exposure to NPE metabolites cause:-
Organisms exhibit sexual dysfunctionality.
An increase in mortality and damage to the liver and kidney.
A decrease in testicular growth and sperm counts in male fish.
Disruption to normal male to female sex-ratios, metabolism,
development, growth, and reproduction.
Many of the current suppliers are reducing the range of NPE’s and some
have even exited that particular market segment. USA suppliers will not
supply to European customers.
Where are we today?
Where are we today? Supplier LSC Cocktail containing NPE's
Perkin Elmer Ultima Gold, Ultima Gold XR, AB, LLT, uLLT & MV
Optiphase Hisafe 2, & 3, Hi-Load & Supermix
Ultima-Flo M, AF & AP
StarScint, Lumasafe Plus, Irgasafe Plus
Insta-Gel Plus. Emulsifier Safe, Hionic-Fluor, Flo-Scints
Filter-Count, Monophase-S & Permafluor E+
Meridian Gold Star, Gold Flow, Gold Star Quanta & Gold Star LT2
MicroFlow G, CarbonCount & TritiumCount
Zinsser Aquasafe 300+, 500+ & 800
Quicksafe A, 400 & N, Filtersafe & Irgasafe Plus
Quickszint 1, 212, 501 & 2000
Oxysolve-T & Oxysolve C-400
National Diagnostics Ecoscint XR, A, H, Flow, Ultra, BD & Bioscint
Ecoscint Original, Oxosol 306 & Oxosol C-14
Hydrofluor, Liquiscint, Betafluor, Monofluor, Filtron-X
Monoflow 1, 2, 3, 4, 5 & Soluscint XR
Roth Rotiszint Eco Plus & Rotiszint Eco
Where are we today?
Supplier LSC Cocktail WITHOUT NPE's Perkin Elmer Pico-Fluor Plus & Biofluor Plus
(Based on Pseudocumene)
Meridian ProSafe+, HC+ & FC+.
ProFlow G+ & P+
(All based on DIN)
Zinsser Quicksafe Flow 2
(Based on DIN)
What will be the next
driving force?
Legislation?
Environmental?
Assay development?
Who will be around?