蒸馏水NO_3与NO_2杂质检查假阳性结果的成因及防止

 将中国药典（１９９０年版）蒸馏水中与杂质检查法倒置应用，首先检查了所用试剂（液）自身的致阳性状况，探明了诱发假阳性的４种可能因素：醋酸和冰醋酸的致假阳性率分别为６６．６％（４／６）和５０％（３／６）；采用合阳性杂庙的醋醚、冰醋酸或水（三者之一）所配成的Ｇｒｉｅｓｓ’ｓ液；锌粉过量；操作不当所致的污染。试验还证明，醋酸酐在未完全水解之前不仅不能代替醋醚，相反对与杂质检出有间接的掩蔽作用。

Formation and prevention of false positive results while detecting/ impurities in distilled water

The reagents were first examined for their causation of false positive results by in-verted usage of the method for detecting NO￣-_3/NO￣-_2 impurities in distilled water in Chinese Phar-macopeia(1990). The following 4 probable factors were ascertained. The percentages of the falsepositive results caused by acetic acid and acetic acid glacial were 66.6%(4/6 ) and 50%(3/6)respectively. Griess’s charge prepared with acetic acid,acetic acid glacial or water containing posi-tive impurities were used. Excessive zinc powder was used. Contamination was caused by misop-eraiton. Experiments proved that before incomplete hydrolysis,acetic anhydride not only couldn’treplace acetic acid,but also had indirect masking action for the detection of impurities.