The Analytical Facilities of the School of Environmental Sciences (ENV) offer isotope analysis of nitrate in freshwater and seawater samples for δ15N, δ18O and δ17O using the denitrifier method (Sigman et al. (2001), Casciotti et al. 2002, Kaiser et al. 2007). Please send enquiries to Sarah Wexler or Jan Kaiser.
We prepare your samples using a bacterial strain that converts nitrate and nitrite in an aqueous sample to nitrous oxide gas. The nitrous oxide in the sample vial is purged from the vial with helium using a double needle, passed through a Nafion drier to remove water, through a sodium hydroxide and magnesium perchlorate scrubber to remove CO2 and further water, a dry ice/ethanol trap (–78 °C) as final drying step, and a trap to remove volatile organic compounds (VOCs). The sample is preconcentrated using liquid nitrogen, passed through a gas chromatograph with a PoraPLOT Q column to separate out any remaining CO2 and VOCs and analysed on a GEO 20-20 isotope ratio mass spectrometer at m/z 44, 45 and 46, from which ratios δ15N and δ18O values are calculated. For δ17O analysis, the nitrous oxide is passed through a gold furnace held at 800 °C to thermally decompose the gas into molecular nitrogen and oxygen, and analysed at m/z 32, 33 and 34 from which δ17O and δ18O as well as the 17O excess, Δ(17O), are calculated.
Samples are calibrated using the nitrate isotope reference materials IAEA-NO-3, USGS 34 and USGS 35, which are prepared and analysed alongside samples in each batch. Final results are reported relative to Air-N2 (δ15N) and VSMOW (δ18O) (or VPDB or Air-O2, if desired).
Standard samples: GBP 30 per sample (plus 20 % VAT, if applicable).
|Definition of standard samples|
|Matrix||Freshwater or seawater|
|Filtration||0.2 μm cellulose acetate filters|
|Nitrate + nitrite concentrations||Please provide for all samples.|
|Nitrite < 2 % of nitrate concentration||For all samples|
|Minimum nitrate concentration||δ15N, δ18O: 2 μmol/l; δ17O: 5 μmol/l|
|Analyte amount||δ15N, δ18O: 20 nmol NO3–; δ17O: 50 nmol NO3–|
|Minimum number of samples||30|
If your samples do not fulfil the above criteria, it may still be possible to analyse them. Non-standard samples will be priced accordingly. Please contact us to discuss your requirements.
Please contact us before sending us your samples. We will send you a quote, followed by a contract for you to sign. We will then ask you to send us your samples and will send you a sample submission form. Once you have received the results you will be sent an invoice.
After we request your samples, please send them in clearly labelled plastic bottles or tubes with the lids securely tightened. Complete the sample submission form with unique sample identification numbers (please do not use any special characters (! @ # $ % ^ & * ( ) . / \ +), and the nitrate and nitrite concentrations of the samples. Print the form and enclose it with the samples and also email it to us.