ISO 15681-1:2003规定了流动注射分析（FIA）方法，用于测定质量浓度在0.01 mg/l至1.0 mg/l（P）范围内的正磷酸盐，以及质量浓度在0.1 mg/l至10 mg/l（P）范围内的总磷。可通过改变操作条件来改变应用范围。 ISO 15681-1:2003适用于各种类型的水（如地下水、饮用水、地表水、渗滤液和废水）。 该方法也适用于海水分析，但随着载体和校准溶液适应样品盐度，灵敏度会发生变化。

ISO 15681-1:2003 specifies flow injection analysis (FIA) methods for the determination of orthophosphate in the mass concentration range from 0,01 mg/l to 1,0 mg/l (P), and total phosphorus by manual digestion in accordance with ISO 6878 for the mass concentration range from 0,1 mg/l to 10 mg/l (P). The range of application can be changed by varying the operating conditions. ISO 15681-1:2003 is applicable to various types of water (such as ground, drinking, surface, leachate and waste waters). This method is also applicable to the analysis of seawater, but with changes in sensitivity, by adaptation of the carrier and calibration solutions to the salinity of the samples.