Methods

Laboratory Working Instructions

Reference Methods

GIPSA's reference methods and laboratories are integral components of the official inspection system. Each reference lab uses internationally recognized methods to directly measure the constituent of interest. The data from these labs are used to calibrate our field instruments and/or methods to internationally recognized reference methods, which encourages worldwide confidence in our official inspection results. GIPSA maintains reference methods for moisture, protein, oil, starch, mycotoxins, and fatty acid composition.

Moisture Reference Method

Air Oven is the reference method for moisture in grains and oilseeds. The moisture value is used to adjust the protein and/or oil and/or starch content to a constant moisture basis. A representative sample is weighed and placed in a standardized, forced-draft oven according to the GIPSA standard operating procedures. After the required drying time, the sample is re-weighed and the moisture content of the sample is calculated. The Air Oven reference laboratory supports the moisture meter instruments used for rapid inspection at field locations performing official testing.

Protein Reference Method

The reference method for analyzing the protein content of grains and oilseeds is combustion nitrogen analysis (CNA). A representative ground sample is weighed and the CNA uses heat and pure oxygen to completely combust (burn) the sample. From the resulting gases, the CNA measures the amount of nitrogen and calculates the "as is" protein content of the ground sample. GIPSA's standard operating procedure follows the AOAC International Method 992.23. The CNA laboratory supports the NIRT instruments used for rapid inspection at field locations performing official testing.

Solvent Oil Extraction

The reference method for analyzing the oil content of corn, soybeans, and sunflower seeds utilizes the Soxtec solvent oil extraction method. A representative ground sample is weighed and the oil is extracted using petroleum ether according to the GIPSA standard operating procedures. Upon completion of the extraction process, the "as is" oil content of the ground sample is calculated. This method is a modification of the American Oil Chemists Society Official Method Ac 3-44. The Solvent Oil Extraction laboratory supports the NMR and NIRT instruments used for rapid inspection at field locations performing official testing.

Polarimetry (Starch) Method

Polarimetry is used to determine the starch content of corn. This is a technique which measures the rotation of the plane of polarized light OR the degree of polarized light passing through an optical sample (ground corn), and from this the "as is" starch content is calculated. GIPSA is following the Corn Refiners Association Method A-20.

Mycotoxin Reference Methods

Mycotoxins are toxic substances produced by a wide variety of fungi (molds). GIPSA has been asked by farmers, grain dealers, and foreign buyers to quantitatively measure aflatoxin, vomitoxin, zearalenone, and fumonisin. GIPSA's Mycotoxin Reference Methods for aflatoxin, vomitoxin, zearalenone, and fumonisin support the evaluation and standardization of rapid test kits used in the official inspection system.

Fatty Acid Composition

Sunflower seed producers are modifying their products to specifically address the amount and types of lipids in their seeds to meet market demands. In FY 2003, in order for these value-enhanced oilseeds to be effectively marketed, GIPSA implemented a new reference method for the analysis of fatty acid composition. GIPSA's standard operating procedure follows AOCS Method Ce 1-62 and Ce 2-66.