Pipette Experiment--Smoking From the Same PipeEverything pertaining to Ar-Ar dating belongs here.
Moderator: Sidney Hemming
8 posts • Page 1 of 1
Happy New Year All-
We are posting this content on the EARTHTIME forum (https://earth-time.org/) and the new blog site (http://argonexperiment.blogspot.com/) as well as in this e-mail. We tried to be comprehensive with the e-mail list. If you notice a lab that we overlooked, please forward this along and alert us about our omission.
For those of you that could not attend AGU last month, we would like to update the Argon community as to the status of the pipette experiment, (discussed at the Colorado EARTHTIME meeting). Just before AGU, NSF notified us that they were going to fund the pipette experiment. At AGU, we presented an update of were the pipette experiment design and goals, summarized below:
I.) EARTHTIME GOAL
Apply high-precision geochronology and quantitative chronostratigraphy to sequence Earth’s history with analytical uncertainties approaching 1‰ of the radioisotopic age(s).”
II.) STATEMENT OF THE PROBLEM
Dispersion among labs participating in inter-calibration is ~2%, and this is substantially greater than the reported analytical precisions (mostly 0.1-0.5%)
III.) Possible Cause(s)
1) differences in the data reduction protocols employed by the participating labs,
2) unaccounted nonlinearity of the mass spectrometer source/detector systems used to collect the data,
3) previously unrecognized heterogeneity in the mineral standards or an experimental artifact arising from neutron dosage variations in some of the irradiation sample packages;
4) incomplete degassing or isotopic fractionation of Ar from the analyzed sanidines as a consequence of inconsistencies in the power and wavelength of lasers used for gas extraction in various laboratories.
5) gas chemistry--different getter clean-up efficiencies of the of sample gas
IV.) PLAN TO ADDRESS/TEST FOR THESE "PROBLEMS"
1) Construct a pipette system. A pipette system that will travel between the participating 40Ar/39Ar labs.
2) A pipette system will permit the participating labs to measure gas samples with exactly the same isotopic composition(s)
3) Measuring the same gas controls the variables and issues associated with sample heterogeneity.
4) Variable gas sample volumes from the pipette system will also be measured to assess the linear/nonlinear response of noble gas mass spectrometers.
V.) WHAT IS NEEDED FROM THE COMMUNITY
1) Source sensitivity from the participating lab for final planning of the pipette volumes
2) Estimated ideal range of Ar abundances for measurement (detector and background constraints)
3) Commitment of about 1-2 weeks of mass spec time to measuring gas samples from the three pipettes
This project will require a fair amount of coordination and communication among the participation labs, so please check the EARTHTIME forum (https://earth-time.org/) and/or the new blog site (http://argonexperiment.blogspot.com/) on a regular bases.
Below is a short questionaire that we will need to help with the implementation of the pipette experiment
1) Is your lab interested in participating in the pipette experiment?
2) What mass spec system(s) are you planning on using for the experiment?
3) What is the sensitivity of your mass spec? Please express the mass spec. sensitivity in amps/mole or *cps/mole
*counts per second
4.) What is the optimum sample size for your mass spec? Please express in terms of moles?
5) What are your "normal/typical" blanks/backgrounds for the 5 Ar isotopes? Please include your "mass spec" blanks/backgrounds and your procedural blanks/backgrounds normalize for a 60 sec clean-up time.
We will need these data to finalize the design of the pipette system to optimize the pipette volume(s) for all of the participating labs.
The four labs who are leading the pipette experiment are Rutgers, Arizona, BGC and Lamont. Below are the estimated sensitivities for these labs:
Arizona Nobles I: 10.9 A/mol
Arizona Nobles II: ~10.9 A/mol
BGC MAP215-50: 8.0 A/mol
BGC MAP215: ~8.0 A/mol
BGC Nobles: 13.5 A/mol
Lamont: VG5400: 9.6 A/mol
Rutgers MAP215-50: 7.1 A/mol
Thank you all in advance and Happy New Year!
Brent Turrin, Carl Swisher
Kip Hodges, Thijs Van Soest,
Al Deino, Paul Renne
Dr. Brent D. Turrin
Assoc. Research Professor
Department of Earth and Planetary Sciences
Rutgers, The State University of New Jersey
610 Taylor Road, Piscataway, NJ 08854
tel. 732-445-3177 fax. 732-445-3374
Last edited by bturrin on Wed Jan 12, 2011 12:26 pm, edited 1 time in total.
I have been putting together the scans you requested as well as assessing the background information toward the goal of planning the best gas abundances for the pipette experiments. My current baselines average about 8e-6 nannoamps (I’m using an analogue multiplier). The 40 signal on a 4e-14 moles air pipette is approximately 1 nannoamp. The mass spectrometer background for 40 is ~1e-4 nannoamps (pumped with ion pump). The 36 background is ~2e-5 nannoamps (thus the 40/36 of the mass spec blank is ~5 and most of the 36 is not Ar). If I wait for a couple of days after venting, the procedural blank for a 5 minute extraction line procedure is 8e-3 nannoamps, and the 40/36 is ~150 (i.e. ~1/2 of the 36 background for my best full procedural blanks is not Ar).
So 4e-14 puts me in at a sample to background ratio of more than 100 for the 40, but the 36 is not so good for air, and the ratio gets accordingly lower and lower for a similar gas load and progressively more radiogenic Ar.
( Scene: a darkened stage, to the sound of crickets)
Hello, anybody out there?
So far we have only receive one reply from the Ar community (University of Arizona Noble Gas Lab).
Come on folks, step up. It is getting awful lonely here.
PIpette Experiment coordinators
I was browsing the AGU abstracts and didn't see one for the experiment.
Is there a short progress report for the ET community that could be summarized here?
Sid and I have received a few inquiries on the status of the Ar pipette project so here is a brief update of where the project stands.
On June 1st, the contract was awarded:
CONSTRUCTING THE PIPETTES
Before cutting stainless steel (measure twice cut once concept) reviewed information from those that responded to our request for mass spectrometer sensitivity information. Based on this information, we finalized the design on pipettes and experiment.
The job request was submitted to the machine shop on/about ~July 1st for the pipettes and bulbs. The project requires 6 bulbs and 18 pipettes. So we had 2 extra bulbs 12 extra pipettes made to cover any manufacturing errors. (Good thing an error in the automated lath firmware mangled one of the pipettes and we lost about 2 weeks waiting for software upgrade from manufacture).
Twenty-three of the pipette bodies are completed. However, we are still waiting for 10 more 1.3-inch mini flanges to finish the last five (We are following up on this. It seems that the remaining flanges should ship this week)
After spending about two weeks chasing down the proper part numbers, The order for the Nupro valve parts went out in late August. (The valve bonnets, bellows, and pneumatic drivers are a special order. Most people order complete valves). There is a 6-8 week delivery time on these parts, so we expect them to arrive soon.
The electronic parts, pneumatic solenoid etc… are ordered and should arrive within the next 2-3 weeks.
In the mean time, we are calibrating the volume and leak testing the bulbs. When we are finished doing this (at Rutgers), we will send them on to ASU and then to BGC for their independent volume calibration(s).
FILLING THE PIPETTES
A sample of a ~9 Ma dacite from the Bodie Hills CA was collected in September. Subsequent processing of the sample has produced ~9 grams of biotite so far. We will irradiate two ~3 gram aliquots, along with nickel wire for an additional neutron flux measure. This will yield approximately 4x10-10 moles of 40Ar* from each aliquot. We are planning on irradiating the biotite to produce a 40Ar*/39Ar ratio of ~1.7 and 41.2 respectively, thus approximating the difference between EARTHTIME co-irradiated Fish Canyon and Alder Creek sanidines experiment.
We submitted a paper for Fall 2011 AGU:
PRESSURE DEPENDANT MASS FRACTIONAION IN NOBLE GAS MASS SPECTROMETERS: A POSSIBLE EXPLAINATION FOR THE EXCESSIVE DISPERSION IN THE EARTHTIME FISH CANYON/ALDER CREEK INTER-CALIBRATION EXPERIMENT
We plan on giving a status update as part of our presentation, but the conveners put our abstract in the poster session. So if you what a detailed update come by our poster. I will see you at AGU in December.
Well the month of June is past and we are looking the 4th of July right in the eye. I hope that you are all having a productive summer. We are steadily progressing and advancing on multiple fronts toward completing the two pipette systems (that is two systems with three canisters and nine pipettes each). Here is an update on our progress.
PIPETTE ASSEMBLY AND OPERATION
Currently we are assembling and leak-testing the two pipette systems. The software to run this system is functioning in the simulation mode. Within the next week or so we should be assembling the pneumatic controls, and then we can interface it with the new software and test the real system.
PRODUCE AND CALIBRATE Ar ISOTOPES
In mid June (6/13-6/15) Sid and I worked with Tim Debey of the USGS on producing the two gases that will represent the relative 40Ar/39Ar ratios of Alder Creek (AC) and Fish Canyon (FC). We weighed out twelve packages of ~1 g each, of a sample of ~ 10 Ma biotite from the Bodie Hills (information on locality and age provided by Bob Fleck). Six of the packages were co-irradiated for 37 minutes. This should yield a 40Ar*/39Ar ratio of ~40, close to the ratio measured for the FC monitor in the FC/AC intercalibration experiment. The remaining six packages were irradiated for 14 hours, which should produce a 40Ar/39Ar ratio of ~1.7 (~23.6 times lower than the other irradiation and similar to the AC monitor in the FC/AC intercalibration experiment). Three of the six packages within each group will be fused and split between the master and traveling bulbs/pipettes. The remaining six packets will be held in reserve in case a "do-over" is required.
Within each package we also co-irradiated six Ni wire, geometrically arranged amongst the packages of biotite, following the experiment of Dalrymple et al., USGS professional paper 1176). We plan to use the gamma-counts on 58Co of the Ni wires and to calibrate an absolute delta-flux for the two gases.
PREPARATION FOR GAS EXTRACTION
As described above, approximately 3 g of material from each group will be fused and split between the master and traveling bulbs/pipettes. Since Ar extraction systems have evolved toward extracting smaller and smaller amounts of material fusing 3 g of material is a back to the future problem that we face. Laser fusion-extraction systems are not really able to fuse 3 g of material and most double vacuum systems pretty much max out at about 1 g of material. We are looking into using a modified K-Ar extraction system at he USGS in Menlo Park CA to fuse the biotite. We have removed the zeolite-water trap and Cu/CuO getter and replaced them with two inline 195° K (Isopropyl alcohol/dry ice) water traps. The Ti-getter has been retained for removing the active gases (N2, CO2, etc..). The gas sample will be collected on an activated charcoal ampule and removed at a flame-seal joint. The ampule also have a “break-seal” that will facilitate transferring the sample gas into the two pipette bulbs.
Bob Fleck and Andy Calvert have been working on developing/ fine tuning the procedure and have done a series of “blank” extractions. We are setting up to measure them next week.
We are over halfway through measuring the two calibration volumes. The experiment is being run completely blind. They have so far been measured at Rutgers, ASU, and BGC the results. Presently, the measured volumes agree at the 0.5‰ level. Once the two bulbs return, Lamont will make their volume measurements and then we will proceed with the volume calibration of the bulbs, pipettes and manifold volumes of the two systems. Ultimately, the pipette systems will deliver calibrated volumes of Ar as well as two Ar gas samples with a calibrated Δ-R.
REAL WORLD EXPERIMENT(S)???
Meanwhile in our quest to probe the reasons for interlaboratory differences, several groups have organically organized to measure the same sets of samples. One example of this, on the ca. 314 Ma Fire Clay tonstein, will be presented at the Goldschmidt meeting next week. Five labs have independently measured sanidines from the Fire Clay tonstein. The good news is all labs report measurement precisions at the ~1 ‰ level. Further good news is that the average of the analytical results from all labs has a standard deviation of only 2.4‰, corresponding to an MSWD of about 10, indicating that the dispersion is greater than expected given reported internal precisions for each lab. We hope that these and additional precise analyses will help us to understand the reasons for this excess dispersion.
If any of you have other ongoing interlaboratory tests, we would like to know about them.
Hi All, In preparation for GSA, we have updated the progress report on the pipette experiment. I'm posting this for Brent who is still not fully out of the post-Sandy recovery. Sid
EARTHTIME pipette experiment for 40Ar/39Ar dating
The EARTHTIME Ar pipette experiment is a significant step in the quest to inter-laboratory consistency at a high precision. The system is currently under construction at Rutgers (Figure 1) and will consist of three 1-liter bulbs loaded with (1) atmospheric Ar, (2) Ar from an 8 Ma biotite irradiated for 0.67 hours (“Fish Canyon”, Figure 2), and (3) Ar from an 8 Ma biotite irradiated for 14 hours (“Alder Creek”, Figure 2). Each bulb will be connected to a sequence of pipettes that allows drawing 0.1, 0.2 or 0.4 cc of gas or combinations of these volumes (Figure 2).
We have tested the volumes of the bulbs and pipettes and we are confident that the pipette system will be capable of delivering a pipetted volume of gas known to within 2‰. During the summer 2012, two different 39Ar “spiked” gas compositions were produced by irradiating two different splits of an 8 Ma biotite. Each split consisted of two ~3g packets of biotite (one 3g packet for the experiment of one for a backup) for a total of 6g each. One of the splits was irradiated for 14 hours and the other for 0.67 hours, producing 40Ar/39Ar ratios similar to Alder Creek sanidine (ACS) and Fish Canyon sanidine (FCS), respectively. Within each package, several Ni wires was also placed in a controlled geometry within the sample packets.
The size of the biotite samples has proved to be a hurdle. Today most 40Ar/39Ar labs designed their extraction systems for measuring smaller small samples, typically in 1-100 mg range. Fusing a 3g packet in these more recently built extraction system is not feasible without significant development. We are thus collaborating with Bob Fleck, Andy Calvert, and James Saburomaru of the USGS, to use the original K-Ar extraction line(s) at Menlo Park. We have successfully extracted unirradiated 3g biotite samples and loaded the gas into one of the pipette systems. So the procedure is now in place to extract the “spiked” gas.
The software development is near completion. The final step in the development cycle requires the hardware to be finalized. The software will track the depletion of the three pipettes reservoir bulbs and calculate the amount of sample gas delivered in real time. The system status is display in a graphic user interface (GUI) (Figure 2).
The construction, manufacturing and assembly phase of the two pipettes is nearly complete (Figure 1). During leak testing of the manifold in September, we did find vacuum leaks in a few of the welds. Further evaluation led to a slight redesign of the manifold to improve the “travel worthiness” of the system, which is necessary since the pipette system will be shipped to the participating labs. In addition, the redesign allowed for leak testing of subcomponents of the manifold, all of which have now passed leak testing. Currently, we are reassembling all of the subcomponents of two pipettes and preparing for a “total system” leak test.
We hope to be testing the system on the Rutgers and LDEO labs and making the initial measurements before the end of 2012, and we hope to be sending it around to participating labs soon afterwards. We hope all the data can be acquired by the summer of 2013 and can be presented at the following Goldschmidt or AGU meeting.
Our vision is to expand this model to supply all interested labs with this type of system with the identical mixed gas standards for all (with some requisite demonstration of efforts analogous to those in place for the U-Pb tracers). For subsequent experiments we will likely use ancient mica for the 40Ar* and zero-age potassium-rich glass for the 39Ar in order to achieve highly radiogenic gas and to minimize the size of material that must be fused. We will also incorporate other information that we learn as we proceed through this initial pipette inter-calibration experiment.
Good news to report for a pipette experiment update, APIS (Argon Pipette Inter-laboratory System). The first APIS is leak-free, and loaded with a "faux gas" which is a biotite of approximately the same age as the one we irradiated, but this one is not irradiated. Thanks to Bob Fleck and Andy Calvert for their help to fuse such huge samples. A series of runs were conducted at Rutgers and the unit is now installed and running tests at LDEO. There was some back and forth to get the MassSpec program upgraded and all the files and scripts in line, but it is now running smoothly (although there are some odd database observations that are troubling at LDEO). APIS 2 has passed the first leak inspection, but the Rutgers lab lost a filament and the sensitive leak tests await being back on line. Meanwhile, we will load some atmosphere into a second bulb, make more measurements and then take it back to Rutgers for a second run, and will probably do a similar dance with the second one before filling the two with the planned experimental gas. One thing that is bothering us is that the gas is not very radiogenic because the biotite is only ~10 Ma, and the fusions had to be made on a relatively high-blank system. So we are considering options for loading the 2 systems with different gases (unlike the original idea of loading them with the same and leaving one back at Rutgers). This ~50% radiogenic gas could be really interesting, particularly for young samples, but we'd also like to have something that is >>90%.
This is just a brief update to show signs of life. Brent will produce a more thorough report with photos and technical details shortly.
Sid and Brent
8 posts • Page 1 of 1
Who is online
Users browsing this forum: No registered users and 1 guest