Mar 22, 2020
Chromatographic separation of strontium isotopes in human dental enamel for Thermal Ionisation Mass Spectrometry (TIMS) analysis
- Esther Plomp1,
- Richard Smeets1,
- Gareth Davies1
- 1Vrije Universiteit Amsterdam
Protocol Citation: Esther Plomp, Richard Smeets, Gareth Davies 2020. Chromatographic separation of strontium isotopes in human dental enamel for Thermal Ionisation Mass Spectrometry (TIMS) analysis. protocols.io https://dx.doi.org/10.17504/protocols.io.37dgri6
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol in our group and it is working.
Created: June 14, 2019
Last Modified: March 22, 2020
Protocol Integer ID: 24517
Keywords: strontium, isotope, human, dental, enamel, TIMS,
Abstract
Protocol for sample collection, dissolution and chromatographic separation of strontium isotopes in human dental enamel for Thermal Ionisation Mass Spectrometry (TIMS) analysis at the Vrije Universiteit Amsterdam, the Netherlands.
Tooth collection
Tooth collection
Collect the teeth in cleaned 50 mL plastic centrifuge tubes (rinsed >3 times with Milli-Q (purified H2O) and 1 time with ethanol (Purity Grade: absolut, CHROMASOLV®, for high-performance liquid Chromatography)). Dry the teeth on a hotplate at 50 °C (mind that plastic melts at higher temperatures).
Tooth cleaning
Tooth cleaning
Leach the teeth for >08:00:00 in 30% H2O2 (Sigma-Aldrich Company Ltd). Put the lids on the tubes but do not seal. After this, rinse the teeth with Milli-Q (>3 times) and dry on a hotplate at 50 °C .
Enamel collection
Enamel collection
Sample the enamel using a micro-drill fitted with a cleaned diamond-tipped rotary burr (Minilor Perceuse).
Burrs should be cleaned before sampling teeth from different individuals and in between multiple samples from the same dental element of one individual to prevent contamination: Rinse with ethanol, place burrs in a container with 3 N HNO3 (Sigma-Aldrich Company Ltd) and ultrasound for 3 minutes, rinse with Milli-Q and ethanol. Let the burrs dry on aluminium foil.
Clean the workspace with ethanol before sampling (especially when sampling different individuals but also in between sampling multiple samples from the same dental element of one individual).
Collect sampled enamel on aluminium foil prior to collecting the enamel in small glass bottles or cleaned eppendorf centrifuge tubes (6-7 N HCl (Sigma-Aldrich Company Ltd) for 5-7 days).
Sample dissolution
Sample dissolution
Clean the PFA laboratory equipment: sub-boil in pro-analysis quality 7 N HNO3 and 6 N HCl for 2 hours each, followed by two leaching steps at 125 °C with (1) double distilled 6.5 N HCl (>5 days) and (2) 7 N HNO3/12 N HF (≥40%Sigma-Aldrich Company Ltd) (>2 days).
Prior to dissolving the enamel, add a 84Sr enriched spike (84Sr/86Sr =1697.79, 10.443 ppb) to the sample to determine the Sr isotope concentration and Sr isotope composition of the same sample. Measure sample and spike bottle weight before and after addition of the spike to calculate the amount of spike added. Add 3-10 drops of spike, depending on sample weight (0.001 g = ~ 3 drops).
Dissolve the enamel in 1-2 ml 14N HNO3 on a hotplate 110 °C (> 08:00:00 ) and re-dissolve in 1–2 mL 6.5 N HCl. Dry (> 12:00:00 ) and nitrate with 3 drops 14N HNO3, dry (> 01:00:00 ), before dissolving in 500 µl 3N HNO3 (> 12:00:00 ). Make sure there is no precipitate in the solution.
Chromatographic separation
Chromatographic separation
Sr is separated from the matrix using 100µL Sr resin columns made from pipette tips.
Ultrasonicate the samples for 30 minutes and centrifuge for 4 minutes at 4000 rpm before loading onto the columns.
Column set up
Rinse the columns 3 times with Milli-Q (MQ) while holding them with an ethanol cleaned tweezer.
Add 100µL Sr resin in a pipette tip (half filled with Milli-Q to prevent air bubbles).
Cleaning of the columns:
1 CV 3 N HNO3
1 CV 1-2 N HF
1 CV MQ
1 CV 3 N HNO3
1 CV MQ
1 CV 3 N HNO3
1 CV MQ
Precondition:
0.5 CV 3 N HNO3
Prefraction (30 CV / 3 mL):
Sample load: 0.5 mL 3 N HNO3 / Tooth Standard load: 0.05 mL (500 ng Sr, 5 mg CaHPO)
Wash: 2.5 mL 3 N HNO3 / Wash: 2.95 mL 3 N HNO3.
Sr extraction (10 CV / 1 mL):
1 mL Milli-Q (collect in clean beakers!)
(Clean the columns and remove the resin using Milli-Q before storage)
TIMS preparation
TIMS preparation
Add 1-2 drops 84Sr spike (20151119, 10.443 ppb) to the blanks. Add 1 drop 0.5 H3PO4 to the samples, blanks and inhouse standard.
Dry samples, blanks and inhouse standard overnight (<08:00:00 ) at 110 °C and nitrate with 4-6 drops of 14 N HNO3. Dry samples, blanks and inhouse standard at 110 °C for TIMS analysis.