SOC functional group abundance (SOC-fga) spectroscopic method

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Method synopsis

A novel method that combines FT-IR and bulk carbon XAS spectroscopy results using a linear mass balance model constrained by elemental analysis to quantify the abundance of seven SOC functional groups. Uses the Beer-Lambert Law where total organic carbon constrains the sum of functional groups from both techniques.

Synthesized from method descriptions across 1 paper using this protocol.

Procedure as described in the canonical source

Steps below were extracted from the paper that introduces this protocol — A molecular investigation of soil organic carbon composition across a subalpine catchment (2018), Soil Systems. Implementations in other papers (listed below) may differ.

1. Elemental analysis
   20-30 mg of ground soil samples or 3-4 mg of biomass samples were weighed into tin capsules and loaded into the analyzer. For total organic carbon (TOC) measurement, 400 mg of ground soil sample was added to a scintillation vial, then 4 mL of 3 M HCl was slowly added via pipette to remove inorganic carbonate. The vial was capped loosely and swirled occasionally for 15 min, then centrifuged to remove supernatant. The soil pellet was washed with deionized water (10 mL × 2), air-dried and ground, then 20-30 mg was weighed into tin capsules and injected.
   Quantities: 20-30 mg soil samples or 3-4 mg biomass samples, 400 mg for TOC, 4 mL of 3 M HCl, 10 mL × 2 deionized water washes, 15 min reaction timeDuration: 15 min HCl reaction timeConditions: Room temperature processing
   Equipment: Carlo-Erba NA 1500 analyzer, scintillation vials, pipette, centrifuge, tin capsules
2. FT-IR spectroscopy measurement
   5-10 mg of ground soil samples or 2-3 mg of biomass sample was loaded directly onto the attenuated total reflectance (ATR) detector with a spatula to obtain the IR spectrum for each sample. For mineral-enriched background, 100 mg of ground soil sample was mixed with 0.625 mL of NaOCl (6% w/w, pH = 9.5) and incubated at 80°C for 15 min to allow oxidation of organic compounds. The solution was centrifuged, supernatant discarded, and treatment repeated three times. The soil pellet was then washed with deionized water (10 mL × 2), air-dried, and ground. 5-10 mg was loaded directly onto the ATR detector.
   Quantities: 5-10 mg soil or 2-3 mg biomass samples, 100 mg soil for background, 0.625 mL NaOCl (6% w/w, pH = 9.5), 15 min incubation, 3 treatment repetitions, 10 mL × 2 water washesDuration: 15 min incubation per treatment cycle, 3 cycles total

Typical Equipment

• Carlo-Erba NA 1500 analyzer
• Nicolet iS50 FT-IR spectrometer
• SGM beam line (11ID-1)
• Canadian Light Source

Output Measurements

• carbonyl abundance
• aliphatic abundance
• amide abundance
• quinonic abundance
• aromatic abundance
• phenolic abundance
• O-alkyl/polysaccharide abundance

Papers Using This Protocol (1)

Species Studied With This Protocol

Places Where Used