National Commission for Certifying Agencies

National Commission for Certifying Agencies (NCCA). Washington, DC at www.credentialingexcellence.org. 

Reference materials for combustion calorimetry have been recommended by the lUPAC Commission Physicochemical Measurements and Standards [130-132] and by the ICTAC Thermochemistry Working Group [133]. They are classified as primary, secondary and tertiary reference materials and when their properties are certified by a national or international organization, agency or laboratory authorized they are called certified reference materials . For combustion calorimetry, the recommended reference materials must be selected according to the atoms in the molecule and its physical state [133] benzoic acid (C,H,0, cr, primary), succinic acid (C,H,0, cr, secondary), hippuric acid (C,H,0,N, cr, tertiary), acetanilide (C,H,0,N, cr, secondary), nicotinic acid (C,H,0,N, cr, tertiary), 1,2,4-triazole (C,H,0,N, cr, secondary)[134], urea (C,H,0,N, cr, tertiary), thiantrene (C,H,0,S, cr, secodary), 4-fluorobenzoic acid (C,H,0,F, cr, secondary), pentafluorobenzoic acid (C,H,0,F1, cr, tertiary), 4-chorobenzoic acid (C,H,0,C1, cr, secondary), 4-bromobenzoic acid (C,H,0,Br, cr, tertiary), 4-iodobenzoic acid (C,H,0,I, cr, tertiary), triphenylphosphine oxide... 

Table 3 Representative certified reference materials for speciation analysis available from European Commission (BCR), International Atomic Energy Agency (IAEA), National Institute for Environmental Studies (NIES), National Institute for Standards and Technology (NIST), and National Research Council Canada (NRCC)...

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