MBL Stable Isotope Laboratory
The more information you provide about your samples, the better the chances for a successful analysis. Please provide a sample list (send electronically if possible) with your submission, including: sample description and identification number, analyses required and estimates of elemental and isotopic composition. Any other relevant information you can provide will be appreciated. You can use our handy-dandy downloadable Sample Submission Form to ensure we get the required information.
Bulk Organic Matter, NH4 & NO3 Salts
Solid materials such as organics (vegetation, animal matter), soils, sediments and NH4 & NO3 salts should be dried and ground to a fine powder to provide the best estimate of isotope and elemental composition.
If you believe there might be carbonate in your bulk sample powders, you should acid treat them to remove it so that the d13C result represents only organically-bound C.
WEIGHING AND PRE-PACKING YOUR OWN SAMPLES
Weighing and pre-packing your own powdered samples saves money and speeds up turnaround-time! We recommend your samples be packed in 5x9 mm tin capsules. Please send along a few empty tins for us to check for background N & C. If you plan on pre-packing your samples, it is important that the correct amount of material be weighed out to optimize analytical conditions. Ideally, we prefer running aliquots having 5-20 micromoles N and/or 10 200 micromoles C. The amount to weigh can be calculated using estimates of %N and %C. The following table is provided as a guideline:
If you pre-pack and weigh your own samples please provide sample weights and estimates of [N] and/or [C]. If you do not pre-pack your samples, please provide estimates of %N and/or %C. In either case, please provide estimates of expected d15N and/or d13C enrichment.
Particulates filters (eg. SPOM, FBOM, EPILITHON) Should Not Be Pre-Packed in tin capsules. We prefer to have a look at them to see how much material is on them, and also how “organic” the material is. This visual assessment allows us to decide how much of the filter can be, or needs to be, loaded into the autosampler. Highly caked filters are usually too large to fit in the autosampler and need to be subdivided. Dark colored material is usually more organic and only a portion of the filter is loaded so that the detectors do not get maxed-out. On the other hand, light-colored material may be highly organic as well, so again please provide as much information (e.g. % N, %C) about each sample as you can to help us make these decisions. Our aim is to obtain the best estimate of isotopic and total elemental composition of the material on each filter.
If you believe there might be carbonate on your filters, you should acid treat them so that the d13C result represents only organically-bound C.
NH4 Diffusion Filters
NH4 diffusion filters should be dried and stored in airtight containers - 20 ml glass scintillation vials work well. Pre-Packing Is Not Required, and in fact is not recommended because, if not completely dry, the damp filter is caustic and will react with the tin capsule producing white SnO? crystals which flake off the packed capsule and wreak havoc with the auto-sampler.
Please provide estimates of [N] and expected d15N enrichment. Have a look at our NH4-Diffusion Protocol document for advice on performing NH4 diffusions.
Please contact us.
NH4 - NO3
We extract dissolved NH4 and/or NO3 from water samples off-line using a NH4-Diffusion Protocol adapted from Sigman et al., 1998 and Holmes et al., 1998. For this method we need good estimates of concentration and d15N composition. This allows us to decide how much of the sample to diffuse, and, in the case of highly 15N enriched samples, how much spike to add reduce the 15N to analyzable levels.
DIC and/or DOC is extracted with an automated TIC-TOC analyzer. For this we need good estimates of DIC and DOC concentration, as well as their predicted d13C composition.
Please contact us if you plan on sending samples for triple oxygen productivity determinations.
It is recommended that water samples for d18O and/or d2H be collected and sent in 20 ml glass scintillation vials having polyethylene-lined caps. The caps should be snuggly tightened, and then taped closed with electrical tape. Wind the tape in the counter-clockwise direction looking from the top as the stretched tape will tend to tighten the lid rather than loosen it if wrapped in the clockwise direction.
AMBIENT GASES IN AIR