The need for new isotope reference materials

Abstract

Isotope reference materials are needed to calibrate and validate analytical procedures used for the determination of isotope amount ratios, procedurally defined isotope ratios or so-called δ values. In contrast to the huge analytical progress in isotope ratio analytics, the production of isotope reference materials has not kept pace with the increasing needs of isotope analysts. Three representative isotope systems are used to explain the technical and non-technical difficulties and drawbacks, on one hand, and to demonstrate what can be achieved at its best, on the other hand. A clear statement is given that new isotope reference materials are needed to obtain traceable and thus comparable data, which is essential for all kinds of isotope research. The range of available isotope reference materials and δ reference materials should be increased and matrix reference materials certified for isotope compositions or δ values, which do not exist yet, should be provided.

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)

“…Their isotope-amount ratios increasingly are being measured in geochemistry, archeology, forensics, and food science, owing to improvements in mass spectrometric techniques such as TIMS (thermal ionization mass spectrometry) or SIMS (surface ionization mass spectroscopy), but mainly owing to the advent of MC-ICP-MS (multi-collector inductively coupled plasma mass spectrometry) [19][20][21]. The latter technique is very versatile in addressing a number of isotope systems in spite of pronounced mass bias effects [22][23][24]. In addition, isobaric interferences need to be evaluated and corrected for accordingly.…”

Metrology

“…A comprehensive discussion about this issue together with an overview of existing isotope reference materials and its proper use were published during the last years and can be found in the respective documents. [19][20][21] …”

Advances in Isotope Ratio Mass Spectrometry and Required Isotope Reference Materials

“…Therefore only a very limited number of laboratories work in this field. In addition to the described drawbacks the achievable standard uncertainties (k=1) for the certified isotope amount ratios are currently limited to values between 0.01% and 0.001%, which is larger than the precision obtained with current multi-collector mass spectrometers 25,44) (Table 1). To bypass this uncertainty problem and potential homogeneity issues with solid materials, so-called δ-reference materials in solution have been suggested by a number of scientists for all elements.…”

“…To bypass this uncertainty problem and potential homogeneity issues with solid materials, so-called δ-reference materials in solution have been suggested by a number of scientists for all elements. 25,[44][45][46] Elemental Solutions in principle can be produced with a homogeneity of better than 0.001%, expressed as relative standard deviation. This homogeneity can be checked by using the most precise analytical procedure for carrying out repeated measurements for the isotope ratio of interest in on a substantial number of units of the candidate material.…”