Hi everyone,
One of my users would like to measure the thallium content in a sulfide. There's likely to be several weight percent Tl present, not trace amounts. Does anyone out there have an appropriate standard material they would recommend? I have seen some comments about thallium bromides and iodides - does anyone have experience with how beam-stable these are? Also, it appears there are some toxicity issues with thallium - does anyone out there who has prepared thallium standards have any advice about minimizing risks?
Thanks,
Em
Quote from: emma_fisi on February 11, 2026, 11:56:41 AMOne of my users would like to measure the thallium content in a sulfide. There's likely to be several weight percent Tl present, not trace amounts. Does anyone out there have an appropriate standard material they would recommend? I have seen some comments about thallium bromides and iodides - does anyone have experience with how beam-stable these are? Also, it appears there are some toxicity issues with thallium - does anyone out there who has prepared thallium standards have any advice about minimizing risks?
Thallium is very toxic, especially the salts. When Ian Carmichael was a grad student he was picking grains under a binocular scope that had been separated using a Tl heavy liquid. Unfortunately he was licking the brush to get the grains to stick to the brush and within a few weeks all his hair fell out!
Back in the day I got a Thallium compound from Claudio Cermignani (retired) which was useful. Here is what he sent me:
St 829 Tl(Br,I)
TakeOff = 40.0 KiloVolt = 15.0 Density = 7.371 Mount = alkali
From Claudio Cermignani (U of Toronto)
TlI-Tl-Br mixture
XRF analysis by M. Gordon
(75% total, recalculated to 100%)
Approx. half of Fe is machine blank
Elemental Composition
Average Total Oxygen: .000 Average Total Weight%: 99.957
Average Calculated Oxygen: .000 Average Atomic Number: 67.606
Average Excess Oxygen: .000 Average Atomic Weight: 142.523
Oxygen Equiv. from Halogen: 2.749
ELEM: Tl I Br Na Mg Si P S
XRAY: ma la la ka ka ka ka ka
ELWT: 61.441 25.828 11.197 .966 .060 .083 .008 .075
ATWT: 204.370 126.904 79.904 22.990 24.305 28.086 30.974 32.064
KFAC: .5521 .2260 .0777 .0040 .0003 .0006 .0001 .0007
ZCOR: 1.1129 1.1430 1.4405 2.3910 1.7801 1.3232 1.1830 1.0290
AT% : 42.866 29.019 19.980 5.991 .352 .421 .037 .334
ELEM: K Ca Fe Zn Ga
XRAY: ka ka ka ka ka
ELWT: .110 .130 .025 .017 .017
ATWT: 39.102 40.080 55.847 65.370 69.720
KFAC: .0010 .0013 .0003 .0002 .0002
ZCOR: 1.1027 1.0013 .8503 .7800 .8129
AT% : .401 .462 .064 .037 .035
Thanks for the reply (and also yikes! I will make sure my user is not doing anything similar during his sample preparation....) :P
Thallium bromide-iodide is used for infrared optics KRS-6. It is insoluble in water and organics. It is very high purity 99.9999+ Melting point over 400C
In contrast thallium chloride, thallium bromide and thallium iodide are all much softer and "smear" during normal polishing and usually cannot be purchased as good sized crystals.
Claudio Cermignani used thallium bromide-iodide for 20+ years at the University of Toronto and its use was continued as the primary thallium standard by Astimex. NO reports of toxicity during 40 years of normal mounting and polishing using oil-based diamond or alumina. Also NO reports of beam issues with KRS-6.
Collect any polishing residue onto paper towels in ziplock bags and contact your local university chemistry department for best disposal advice.