I doubt they would have been able to help Patterson with low level lead measurements especially involving isotopes, Patterson started his lead work back in the early 50's and by the 1960's he was the world leader in this game.Quote:
Originally Posted by ian
Before Patterson developed his accurate trace lead measurements, even the best labs in the world had analytical blanks for lead measurements of the order of 1ug which is hopeless when trying to measure nano or picogram amounts. Some labs claimed less that this but Patterson was quickly able to show them they were wrong. You need to remember that during the era of leaded petrol the average unwashed human hand was covered by around 100 ug of lead on its surface. This was though of an a natural background and most labs had no idea where it came from. Washing and scrubbing with distilled water reduced that to about 10 ug with the remainder being sort of half embedded in the skin and impossible to wash out. We know this by repeated washing of graduate student hands with dilute nitric acid. Acid washed plastic gloves, plastic lab coats, snoods and overshoes became the fashion statements of day in those labs.
Patterson had to start from scratch with trace lead work. He tested every type of lab ware and material used to make labs and found PVC fume hoods and lab bench tops, and conventional lab glassware contained high levels of lead. HDPE lab ware contained less lead but its use was limited as it could not withstand heating so PTFE & FEP was used (later it was found that HDPE could withstand some washing and it was widely used) All lab ware had to be boiled for days in concentrated nitric and hydrochloric acids and stored for weeks in acidified tubs before it could be used. But before that was possible the cleaning water and commercial grade acids had to be purified because they were all contaminated. The containers to distill and hold the purified acids and lab ware had to be cleaned and the labs rebuilt to remove all PVC and metals like Zn that might contain any lead. The labs might look similar to conventional toxicology labs but when the surface was scratched they were quite different. When we built our large ultra-clean labs in 2000 the builder had consultants visit us with experience in toxicology labs and hospital theatre developments and they could not understand why we had a "no metal, no - PVC" requirements. In the end we hired our own consultant from the US who was an expert in ultra trace metal lab design and he was able to set us up to our specifications. Our benches were made of fibreglass and covered in HDPE sheet and PE film.
After a long effort Patterson got the analytical blanks down to the 50ng level and this enabled him to determine the amounts of lead prehistoric man had in his bones.
This also enabled Patterson to make an accurate measurement of lead in modern polar ice provided he used cubic metres of it but he could still not measure the lead in older ice until
he and his students pushed the analytical blanks down to ng and eventually 10's of pg levels. Even then they still had to use up many Litres of ice.
Isotopic measurements of lead added extra complexity in that in the 1960s the ionisation efficiency of lead was so poor at least 10 ug of lead was needed to see a lead signal in a mass spectrometer let alone measure its isotopic composition. It was not until the 1960's that special ionisation techniques were developed by nuclear scientists to get a signal from less than a ug. Since then special plasma mass spectrometers and ionisation enhancers are now used to measure the isotopic composition of as little as 1pg of sample
It took years of excruciating chicken and egg improvements and unheard of levels of cleaning to get to the sub pg level analytical blanks needed to measure lead in ancient polar ice.
In our lab we used the following protocol and all (apart from step 4) took place in a dedicated ultraclean 6 x 6 m lab that was 10 times cleaner than a conventional operating theatre.
1 water was conventionally and Reverse Osmosis filtered, then doubly deionised water, followed by multiple distillations in special quartz sub-boiling stills.
2 HCl was made using from electronic grade HCl gas bubbled into pure water
3 HNO3 was doubly distilled in a quartz sub-boiling still followed by double distillation using a teflon still.
4 FEP lab ware was soaked in ethanol, regular AR grade Conc HCl, Concentrated aqua regia, Conc HCl, then boiled in 5/10L quartz glass beakers containing dilute HCl and HNO3 for about a week
5 then boiled in teflon baths of pure water for a few days, and then soaked in HDPE baths in dilute HNO3 for a minimum of 6 months with the solution changed ever month.
6 we used a lot of HDPE lab ware and that was soaked for months alternately in water and dilute nitric acid.
At one stage we had something like $25k worth of lab ware just in the cleaning cycle. These days a 1m long segment of ice core can be stood upright inside a freezer cabinet with the bottom end poking through onto the top of a specially made Silicon Carbide hot plate and melted at a few mm per minute and the water drained off direct into the mass spectrometer and up to about 40 trace metals measured simultaneously in the melted water.
