['PAGE', '4', 'OF', '13', 'Interferences', '4.1', 'All', 'reagents', 'must', 'be', 'prepared', 'with', 'reagent', 'grade', 'deionized', 'water', '(>', '10', 'megohm/em', 'or', 'better).', '4.2', 'Volatile', 'amines', 'will', 'pass', 'through', 'the', 'membrane', 'and', 'interfere', 'with', 'ammonia', 'measurements.', '4.3', 'Metal', 'ions', 'which', 'complex', 'ammonia', 'can', 'be', 'an', 'indirect', 'interference', 'causing', 'lowered', 'measurements.', 'Precision', 'and', 'Bias', '5.1', 'A', 'precision', 'study', 'of', 'this', 'procedure', 'was', 'carried', 'out', 'for', 'ten', 'days.', 'Six', 'tobacco', 'samples', 'with', 'ammonia', 'levels', 'ranging', 'from', '0.14%', 'to', '2.52%', 'were', 'used', 'in', 'this', 'study.', 'This', 'procedure', 'gave', 'relative', 'standard', 'deviations', '(RSD)', 'of', '1.8%', 'to', '9.5%', 'in', 'ammonia', 'determination.', 'This', 'procedure', 'showed', 'significant', 'day-to-day', 'variation', 'in', 'all', 'tobacco', 'sample', 'analyses.', '5.2', 'Each', 'day', 'six', 'tobacco', 'samples', 'were', 'analyzed', 'in', 'three', 'replicates', 'during', 'a', 'ten-day', 'period.', 'The', 'results', 'of', 'tobacco', 'sample', 'analyses', 'are', 'summarized', 'in', 'Figure', '1.', 'Estimated', 'day-to-day', 'and', 'within-day', 'variations', 'are', 'given', 'in', 'Figure', '2.', '472000969', ' ']