Tuesday, 29 June 2010

AOAC Official Method 2000.04 Iodine-131 in Milk Radiochemical Separation Method First Action 2000

(Applicable to determination of iodine-131 in milk at 0.1-0.3 Bq/L.)
Caution:    This method requires the use of a chlorinated solvent, C(b), a suspected and possible human carcinogen.
See Table 2000.04 for the results of the interlaboratory study supporting acceptance of the method.

A. Principle

The test portion is treated with NaHSO3 to convert all the iodine to a common (I-) oxidation state. Iodide is isolated and concentrated on an ion-exchange column. The iodide is oxidized on-column to iodate by NaOCl solution and eluted by this solution. The NaOCl is decomposed and the iodate is reduced by hydroxylamine hydrochloride solution to elemental iodine which is extracted by CC14. The iodine is again reduced to iodide and re-extracted into aqueous solution by NaHSO3 solution. The iodide is coprecipitated with palladium iodide (PdI2) and the recovery of the carrier is determined gravimetrically. The iodine-131 in the carrier is counted by a beta-gamma coincidence or by a low-background beta counter.

AOAC Official Method 2000.03 Ochratoxin A in Barley Immunoaffinity by Column HPLC First Action 2000

(Applicable to the determination of ochratoxin A in barley at >1 ng/g)
See Table 2000.03A for results of the interlaboratory study supporting the acceptance of the method.

A. Principle

Test portion is extracted by blending with acetonitrile-water. The extract is cleaned up by passing through an immunoaffinity column. Ochratoxin A (OTA) is eluted with methanol, further purifed and identified by LC, and quantified by fluorescence.

AOAC Official Method 2000.02 Patulin in Clear and Cloudy Apple Juices and Apple Puree Liquid Chromatographic Method First Action 2000

(Applicable to determination of patulin at >25 ng/g in clear apple juice, cloudy apple juice, and apple puree.)
See Table 2000.02 for results of the interlaboratory study supporting the acceptance of the method.

A. Principle

Apple juice or puree is extracted with ethyl acetate and then cleaned up by extraction with sodium carbonate solution. (Cloudy apple juice and apple purees are pretreated with pectinase enzyme.) The ethyl acetate extract is dried with anhydrous sodium sulfate. After evaporation of the solvent, patulin is quantitatively determined by LC with UV detection.

AOAC Official Method 2000.01 Determination of 3-Chloro-1,2-Propanediol in Foods and Food Ingredients Gas Chromatography/Mass Spectrometric Detection First Action 2000

[The method is applicable to the determination of 3-chloro-1,2-propanediol (3-monochloropropane-1,2-diol; 3-MCPD) in hydrolyzed vegetable protein (HVP), soups and stocks, stock cubes, soy sauce, malt extract, salami, fish, cheese, flour, starch, cereals, and bread.]
Caution:    This work should be performed under a fume hood. Wear laboratory coat, gloves, and eye/face protection. Use double-containment systems for handling concentrated solutions of 3-MCPD-d5. Take care to avoid ignition of flammable reagents by sparks or static discharge.
See Table 2000.01 for the results of the interlaboratory study supporting acceptance of the method.

A. Principle

Internal standard 3-chloro-1,2-propanediol-d5 (3-MCPD-d5) is added to the test portion, followed by salt solution, and the mixture is blended to a homogeneous consistency. After sonication, the contents of an ExtrelutTM refill pack are added and mixed thoroughly. The mixture is transferred to a glass chromatographic tube, and the nonpolar components are eluted with a mixture of hexane and diethyl ether. The 3-MCPD is eluted with diethyl ether, and the extract is concentrated to a small volume. A portion of the concentrated extract is derivatized and analyzed by gas chromatography with mass spectrometric detection (GC/MS). The concentration of 3-MCPD is expressed in mg/kg.

AOAC Official Method 2002.05 Determination of Cholecalciferol (Vitamin D3) in Selected Foods Liquid Chromatography First Action 2002

A. Principle

After the addition of an internal standard (vitamin D2) and basic hydrolysis, vitamin D3 is extracted with n-heptane. The fraction that contains vitamin D2/D3 is separated by preparative normal-phase liquid chromatography (LC). After evaporation and dilution in acetonitrile–methanol, vitamin D3 is determined by reversed-phase LC with UV detection at 265 nm. A separate test portion is analyzed in parallel to confirm the absence of endogenous vitamin D2.

AOAC Official Method 2002.04 Amylase-Treated Neutral Detergent Fiber in Feeds Using Refluxing in Beakers or Crucibles First Action 2002

A. Principle

Fiber in feeds is a nutritionally defined entity that represents the indigestible and slowly digesting fraction of feeds. Neutral detergent (ND) solution and heat-stable alpha.gif (53 bytes)-amylase are used to dissolve easily digested proteins, lipids, sugars, starches, and pectins in feeds, leaving a fibrous residue that is primarily cell wall components in plant materials (cellulose, hemicellulose, and lignin) and indigestible nitrogenous matter in animal products. aNDF is a gravimetric method that best estimates the total insoluble fiber, and is inversely related to digestibility and intake potential of a feed. ND soluble matter is almost completely digested by most animals; however, the digestibility of aNDF is variable among feeds and is related to lignin and other constituents in fiber.
Sodium lauryl sulfate, an anionic detergent, and sodium sulfite are used to solubilize nitrogenous matter; EDTA is used to chelate calcium and enhance removal of pectins at boiling temperatures; triethylene glycol helps remove some nonfibrous matter from concentrated feeds; disodium phosphate and sodium borate are used as buffers to maintain a neutral pH.
Hot ND solution has limited ability to solubilize starch; therefore, a heat-stable amylase is used to hydrolyze starch to saccharides that can be easily removed from fiber by filtration. Heat-stable amylases are used in hot solutions to inactivate potential contaminating enzymes in crude amylase extracts that might degrade fibrous constituents. To ensure that the amylase activity is sufficient to remove most starch and to reduce filtering difficulties, the amount of any specific amylase source needed to measure aNDF is determined under the conditions of the aNDF method.
Although boiling ND solution dissolves most proteins, lipids, and nonfibrous carbohydrates, these constituents are nonviscous only in water that is near boiling temperature. Therefore, boiling water is needed for washing fibrous residues and removing nonfibrous matter. Because fiber is particulate matter, mass-action equilibration during soaking is needed to migrate ND and contaminating soluble matter from the interior of fiber particles. Fibrous residues must be soaked, instead of being simply rinsed, in near boiling water to remove nonfibrous matter.
Boiling ND solution solubilizes lipids, and acetone soaking of the residue completes the extraction of lipids and pigments in most materials. However, excessive amounts of lipids in materials can complex with the detergent and reduce extraction efficiency. Because extraction of lipids by ND and acetone may be incomplete when feeds contain >10% lipid, these materials are pre-extracted to ensure complete removal of lipid contamination from fiber. Pre-extract materials with 5–10% lipid to minimize filtration difficulties and avoid variable aNDF results.

AOAC Official Method 2002.03 Pesticide Residues in Nonfatty Foods Supercritical Fluid Extraction and Gas Chromatography/Mass Spectrometry First Action 2002

A. Principle

A chopped frozen fruit or vegetable test portion is mixed with a drying agent, and the pesticide residue is extracted by using supercritical CO2, collected on a solid-phase sorbent or in a liquid trap, and determined by GC/MS.