酚二磺酸光度法测定水中硝酸盐氮时,水样若有颜色应如何处理?
每100ml水样中加入2ml氢氧化铝悬浮液,密塞充分振摇,静置数分钟澄清后,过滤,弃去最初的20ml滤液。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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