High Precision Zinc Isotopic Measurements Applied to Mouse Organs

Summary

We present the technique to measure with high precision zinc isotope ratios in mouse organs.

Abstract

We present a procedure to measure with high precision zinc isotope ratios in mouse organs. Zinc is composed of 5 stable isotopes (⁶⁴Zn, ⁶⁶Zn, ⁶⁷Zn, ⁶⁸Zn and ⁷⁰Zn) which are naturally fractionated between mouse organs. We first show how to dissolve the different organs in order to free the Zn atoms; this step is realized by a mixture of HNO₃ and H₂O₂. We then purify the zinc atoms from all the other elements, in particular from isobaric interferences (e.g., Ni), by anion-exchange chromatography in a dilute HBr/HNO₃ medium. These first two steps are performed in a clean laboratory using high purity chemicals. Finally, the isotope ratios are measured by using a multi-collector inductively-coupled-plasma mass-spectrometer, in low resolution. The samples are injected using a spray chamber and the isotopic fractionation induced by the mass-spectrometer is corrected by comparing the ratio of the samples to the ratio of a standard (standard bracketing technique). This full typical procedure produces an isotope ratio with a 50 ppm (2 s.d.) reproducibility.

Introduction

The measurement of high-precision (better than 100 ppm/atomic mass unit) zinc stable isotope composition has only been possible for about 15 years thanks to the development of multi-collector plasma-source mass-spectrometers and has since been mostly applied in Earth and planetary sciences. The applications to the medical field are novel and have a strong potential as biomarkers for diseases that modify the metabolism of zinc (e.g., Alzheimer disease). This paper reports a method to measure with high precision the natural stable isotope ratios of zinc in various mouse organs. The same would be applicable to human samples. The method consists of the dissolutio....

Protocol

NOTE: Procedures involving animals have been approved by the Institutional Animal Care and Use Committee (IACUC) at the Université Paris Diderot.

1. Preparation of Materials

1. Sub-boil distill 1 L of the acids (HNO₃, HBr) in order to purify them from impurity.
2. Clean the beakers and tip adaptor in a hot (~ 100 °C) concentrated HNO₃ acid bath for at least two days.
3. Wash the pipette tips in a cold 3 N HNO₃ bath for several days and rinse individually three times with de-ionized water.

2. Sample Preparation

1. Anesthetize the mice by intraperitoneal ....

Results

In 1.5 N HBr, the main zinc species (ZnBr3-) forms very strong complexes with the anion-exchange resin, while most other elements do not interact with the resin. Zinc is then recovered by changing the medium to diluted HNO₃, changing the speciation of Zn to Zn²⁺ which is released from the resin^6,7.

Isotope ratios are typically expressed as parts per 1,000 deviations relative to a standard:

Discussion

The reproducibility of the measurements is evaluated through replicated analyses of the same samples carried out during different analytical sessions. For example⁶, we have replicated the same terrestrial rock 7 times and we obtained the results reported in the Table 2.

As expected from the theory of isotopic fractionation¹⁰ and as measured in any solar system material so far (e.g., meteorite^11-13, plants^3-5, deep-sea s.......

Materials

Name	Company	Catalog Number	Comments
Name of Material/ Equipment	Company	Catalog Number	Comments/Description
Multi-collection inductively-coupled-plasma mass-spectromter	Thermo-Fisher
Anion-exchange resin AG1 X8 200-400	Bio-Rad	140-1443-MSDS
teflon beakers	Savillex	200-015-12
Home-made teflon colunms made with shrinkable teflon