Mass Spectrometers

NIWA's state of the art Isotope Ratio Mass Spectrometry (IRMS) facility supports our research and commercial analyses, providing tailor-made solutions for various environmental and atmospheric questions. Our purpose built facility houses high precision MAT252 and MAT253 mass spectrometers, equipped with Thermo Scientific Kiel (III & IV) devices, as well as DeltaPlus mass spectrometers by Thermo Scientific, and a Micromass Isoprime. 

Atmospheric Greenhouse gas studies 

Atmospheric greenhouse and trace gases are measured on the MAT252 and MAT253 utilising both dual inlet and continuous flow. While paleo-atmospheres are studied from ice cores on the Isoprime using a continuous flow technique.

NIWA operates Thermo Scientific MAT252 and MAT253 isotope ratio mass spectrometers in a purpose-built laboratory at Greta Point, Wellington. These instruments are fitted with both continuous flow and dual inlet systems and have been modified to provide precise analyses for various aspects of the environmental research undertaken by NIWA and its clients. In particular, modifications have been made to enable high-precision determinations of δ13C in the atmospheric greenhouse gases, carbon dioxide (CO2) and methane (CH4), as well as the trace gas carbon monoxide (CO). These data have been widely used in studies of the source structure of the gases as well as models examining global climate change.

Carbon dioxide is currently increasing in the atmosphere. While precise concentration measurements allow us to track this increase, it is stable isotopes that allow us to observe how the composition of the atmospheric CO2 is changing. The CO2 analyses involve the online separation of whole air on a chromatographic column, before measurement in a continuous flow mode. These analyses provide both δ13C and δ18O, with precisions of 0.02‰ and 0.04‰ respectively.

Methane is an important greenhouse gas, research into the carbon stable isotope seasonality and variability provide insight into atmospheric processes and transport. Methane isotope analyses at NIWA involve either off-line preparation for high precision, or on-line for small samples. The high precision analyses are aimed at resolving the small seasonal cycle (about 0.2 ‰) in the carbon isotopes of CH4, at mid latitude southern hemisphere this is. To do this off-line preparation allows us to achieve repeatability over many years of better than 0.02‰. The study of paleo-atmospheres using ice cores is constrained by very small sample sizes. For this reason the continuous flow Isoprime is fitted with a pre-concentration and combustion interface, allowing δ13CH4 analyses to be made on a kilogram of ice.

Contacts – Atmospheric greenhouse gas studies

Ross Martin
ross.martin@niwa.co.nz

Gordon Brailsford
gordon.brailsford@niwa.co.nz

Publications

Related greenhouse gas publications.

Stable Isotopes in Carbonates 

Carbonates are studied using the MAT252 and MAT253 which are equipped with Thermo Scientific Kiel (III & IV) devices, providing automated high-precision determinations of δ13C and δ18O in individual foraminifera and other carbonate samples.

NIWA is a leading institute in New Zealand doing high resolution analysis of stable isotopes in carbonates to identify environmental change over timescales of tens to thousands of years. We use these techniques on materials as diverse as foraminfera, shells, fish earbones, and limestone structures in caves. These analyses provide both δ13C and δ18O, with precisions of 0.04‰ and 0.08‰ respectively.

Planktonic foraminifera are single-celled organisms which secrete their tests using oxygen and carbon from the water in which they live. Isotopic analysis on these, and on deepsea corals and brachiopods, tells us much about how the marine climate has changed in the past, including relatively abrupt changes in ocean circulation.

Locked inside speleothems, including stalactites and stalagmites, is a historical record of heavy rain seeping into caves. Isotope analysis here helps define risk assessment models (e.g., for tropical cyclones) and improves understanding of climate changes.

Stable isotopes in coastal fauna such as paua shells provide a picture of local climate variability and help us estimate paua age and growth rate; information vital for assessing the sustainability of these coastal fisheries.

Isotope analysis of fish otoliths (earbones) is clarifying the life histories of some significant commercial species.

These analyses all provide critical information for understanding freshwater, marine, and terrestrial ecosystems, particularly with respect to historical climate change and environment and biology of marine organisms. It is now possible to study past changes in the ocean and climate, provide improved data for climate modelling, and help predict the response of the ocean to climate change. Also to reconstruct seasonal profiles of bygone winters and summers, unravel geographic fish migration patterns and life histories, or even derive daily records of climate for the Miocene (20 Ma).


Contacts – Carbonate Analysis

Dr Helen Neil, helen.neil@niwa.co.nz, or phone +64 4 386 0375

Publications

A selected list of publications illustrates NIWA's recent research using a Kiel device, which provides automated high-precision determinations of δ 13C and δ 18O in individual foraminifera and other carbonate samples.

Mass spectrometry-related publications 

 

ThermoFinnigan DeltaPlus 

An elemental analyser linked to the Thermo Scientific DeltaPlus mass spectrometer enables us to analyse carbon and nitrogen concentrations and isotope ratios in solid and liquid samples from freshwater, marine and terrestrial environments with a focus on ecological studies.

The ThermoFinnigan DeltaPlus is a fully automated continuous flow isotope ratio mass spectrometer (CF-IRMS) that is set up to detect concentrations and stable isotope ratios of carbon and nitrogen.

Samples are introduced to the DeltaPlus via a Carlo-Erba NA1500 CHN elemental analyser (EA) which processes solid and liquid samples into gas samples before analysis on the mass spectrometer.

Computer software integrates the mass spectrometer output data and calculates % weight, atom % and delta values for each element. Sample throughput for dual C and N analysis is 6 samples per hour enabling analysis of up to 100 samples per day. The DeltaPlus has high sensitivity and excellent linearity, resulting in extremely good reproducibility of measured isotope ratios. Precision on 20 repeat reference gas injections is always better than 0.07 ‰ (Table 1). 

Table 1: Precision of 20 repeat reference gas injections of N2 and CO2 (Zero Tests).

  Delta vs. WST 29/28 (‰)     Delta vs. PDB 45/44 (‰)  
Mean s.d. Mean s.d.
–0.04  0.06 0.03 0.04
0.04  0.05 0.06 0.07
0.003 0.03 0.04 0.04

 

Repeat analyses of standards, including urea, acetanalide, flour, DL-leucine, and several international standards demonstrate the excellent accuracy and precision of the DeltaPlus. A selection of results is given in Table 2, with some comparisons against commercial analyses. Even for extremely low sample amounts (20 μg N, and 50 μg C) precision was always better than 0.2‰ and usually less than 0.1‰ for both δ15N and δ13C. These precision data compare extremely favourably with published literature values. 

Table 2: DeltaPlus precision of δ15N and δ13C analyses of standards run consecutively in a batch analysis.

Standard Run type δ15N average (‰) δ15N standard deviation (‰) δ13C average (‰) δ13C standard deviation (‰)
Urea, 0.1 mg International value –1.50   –49.44  
  DeltaPlus, n=10 –1.44 0.07 –49.16 0.13
  DeltaPlus, n=9 –1.48 0.06 –49.18 0.10
  Commercial CF-IRMS, n=4 –1.32 0.60 - -
Acetanalide, 0.1 mg DeltaPlus, n=10 –9.09 0.10 - -
  DeltaPlus, n=10 –9.01 0.07 - -
  DeltaPlus, n=10 –9.10 0.03 - -
  DeltaPlus, n=10 –9.10 0.09 - -
  Commercial CF-IRMS, n=4 –8.24 0.25 - -
Flour, 0.25 mg DeltaPlus, n=10 2.20 0.02 –24.26 0.07
  Commercial CF-IRMS, n=20 1.67 0.14 –24.10 0.05

Research Applications within NIWA

The DeltaPlus mass spectrometer has wide-ranging applications within NIWA's environmental research programmes and also has many commercial applications. Carbon and nitrogen natural abundance variations provide insight into freshwater, marine, and terrestrial ecosystem research as well as atmospheric and agricultural research.

In ecological studies, stable isotopes are an extremely useful determinant of the trophic status of organisms and an indicator of their diet. There is a slight variation in C and N stable isotope values between an organism and its food source, which has resulted in the statement "You are what you eat, plus or minus a few per mil". Nitrogen isotopes are the strongest indicators of trophic status, showing a step-wise enrichment in 15N of about 3–4‰ at each successive trophic level. By combining C and N isotopic values of a consumer, it is possible to deduce its likely dietary intake and resolve complex food web structures.

Nitrogen isotope values can be utilised to identify different sources of nitrogen and indicate pollutant pathways. Several natural processes fractionate nitrogen, e.g. inorganic nitrogen assimilation, nitrogen fixation, nitrification, denitrification, ammonification, and other processes of nitrogen metabolism.

A further interesting application of the DeltaPlus is that of forensic sample characterisation. C and N isotopic ratios can be utilised to validate the authenticity of substances such as drugs (cocaine, heroin), explosives (TNT) and traces of paint.

A valuable application of stable isotopes is that of tracer or enrichment studies. Such studies enable rates of processes to be directly measured by the incorporation of an artificially-enriched stable isotope. This is an extremely powerful experimental method in environmental studies.

Some examples of specific stable isotope research that NIWA is currently involved in include:

  • food web structure in Antarctic freshwater lakes
  • crayfish ecology, aquatic insect ecology and stream food webs
  • nutrient dynamics in lakes, riparian systems and estuaries.
  • nutrient pollution pathways.
  • ecosystem structure across oceanographic frontal zones.
  • phytoplankton research linked to ocean-atmosphere flux studies
  • seabird diet interpretation.
  • enrichment studies in marine, freshwater and terrestrial environments.

Contact – DeltaPlus Facility

We provide competitive rates for commercial analysis of stable isotope samples and are enthusiastic about research collaboration. For information, including enquiries relating to collaborative research or commercial analyses, contact:

Sarah Bury, sarah.bury@niwa.co.nz or phone +64 4 386 0347.

DeltaPlus Publications

A selected list of publications illustrates NIWA’s recent research using the DeltaPlus mass spectrometer.

Mass spectrometry-related publications 

Gordon Brailsford with MAT253 mass spectrometer

Sample gas is frozen back from the MAT253 after stable isotope analysis for later 14C analysis. Credit: NIWA

Wave Micromill

NIWA’s New Wave micromill is used to prepare microsamples for chemical and isotopic analysis. Complex structures can be sampled with submicron stage resolution and positional accuracy. Pictured clockwise top to bottom are: speleothem (being milled), bamboo coral sections, a galaxid otolith, a pair of pilchard otoliths.

Helen O'Neil, NIWA, checking samples

Dr Helen Neil checks samples for a 24 hour carbonate (Kiel and IRMS) stable isotope run. Credit: Dave Allen