BACKGROUNDSoil environmental reference materials are important technical tools for the quality control of soil environmental monitoring. However, there is no self-developed environmental matrix reference material with total organic carbon (TOC). In particular, a soil standard sample supporting the combustion oxidation-non-dispersive infrared method has not been developed yet.

OBJECTIVESTo develop a soil TOC reference material that can support standard methods for the determination of TOC in soil.

METHODSAgricultural land soil with a high organic carbon content was selected as the raw material. The soil TOC reference materials were prepared after drying, grinding, mixing, bottling, and sterilization. Ten bottles of the reference materials were randomly sampled in layers, and their homogeneities were determined using combustion oxidation-non-dispersive infrared (NDIR) absorption method. The data were assessed using a single element analysis of variance. The reference material was stored at room temperature, and its stability was determined for 18 months. The test results were assessed using a linear fitting model. Eleven laboratories were organized as the cooperation to determine the TOC content of the prepared reference material using combustion oxidation-NDIR absorption method and potassium dichromate volumetric method. All measurement data were statistically analyzed to obtain the certified value and uncertainty of the reference material.

RESULTSThe soil TOC reference material exhibited good homogeneity and stability. After evaluation, the F value was determined to be less than the critical value of F_0.05 (9, 10). Additionally, the relative uncertainty (u_bb) of the uniformity between bottles was 1.5%, and the sample exhibited good uniformity. The stability uncertainty was 1.2%, which indicated good stability. The certified value of the soil TOC reference material was determined to be (25.2±1.4)mg/g, using the grand mean of the collaborative determination results from multiple laboratories.

CONCLUSIONSA soil TOC reference material was developed using combustion oxidation-NDIR absorption method. This reference material can be used to support the standard determination methods of TOC in soil and meets the requirements of the studies on TOC content in soil. Moreover, it is comparable with similar foreign samples.