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?