Isotopes of Carbon – DIC

Requirements

  • Samples should be submitted in 60 mL wide-mouth Amber HDPE bottles (Fisher Scientific Cat # 02-925-3B) – Avoid tin foil lined caps!!
  • Samples must be filtered using 0.45 μm luer lock syringe filters (Fisher Scientific Cat # 50-109-8711).
  • Bicarbonate alkalinity (HCO3 mg/L) is a helpful component and should be sent with any correspondence regarding sample submission. This parameter helps us determine how much sample to inject during the methodology phase.
  • Bottles must be submitted with as little headspace as possible, ideally with no headspace (loss of DIC via the headspace will occur over a matter of days).
  • Soon after collection and prior to shipment, refrigerate samples if possible. DO NOT FREEZE.
  • For long term storage of DIC samples on the order of months, a small amount of mercuric chloride can be added to each sample (Fisher Scientific Cat # LC165909). This is to prevent biological buildup, algae formation, and fractionation of the DIC. You must indicate in your correspondence if such a preservative is used.
  • Samples should be sent as soon as possible to our facility. Samples will be refrigerated upon arrival.

Methodology

A series of solid standards with known δ13C are weighed into 12 mL round bottom borosilicate glass Labco exetainer vials (Cat # 938W) and capped. These vials are purged with ultra-high purity (UHP) helium for ten minutes using an offline purge rack. Using 1 mL disposable syringes with 25G needle attached, five to ten drops of 100% prepared phosphoric acid (ρ=1.9023 g/cm3) are injected into the exetainer and allowed to equilibrate for 24 hours at 30 oC. Another series of empty exetainer vials for the samples are labeled, and five to ten drops of the same phosphoric acid is added to each vial, then capped. The sample vials are purged using UHP helium for ten minutes each. Based on the bicarbonate alkalinity, an aliquot of the sample is injected into the corresponding purged exetainer vial, which forces CO2 and H2CO3 from solution to CO2 gas. The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler with ultra-high purity helium acting as a carrier gas. Sample CO2 gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) located inside a Thermo Fisher GasBench II front-end peripheral, then onto a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ13C. Isotope data is corrected for any linearity effects showed by a standard analyzed ten times at variable weight. Precision for δ13CDIC is ±0.08‰.

Turnaround Time

  • ≤ 60 samples: 2-3 weeks to process.
  • > 60 samples: 4-6 weeks to process.