The molybdenum blue method is the American Public Health Association (APHA) approved method for the detection and quantification of phosphate in water. The standard molybdenum blue method, APHA 4500 PE has a detection limit of 30 μgL⁻¹ phosphate (10 μgL⁻¹ phosphorus) in freshwater with a 5 cm cuvette. To further lower the detection limit to sub μgL⁻¹ levels, we have developed a simple, fast, and solventless method for conversion of phosphate present in solution to a solid for quantification by Visible spectroscopy. The process converts the anionic heteropolymolybdate ions into a solid colloidal precipitate by charge neutralization with the cationic surfactant cetyltrimethylammonium bromide (CTAB), and the precipitate is then captured on a Visible transparent membrane. A Visible spectrum is then recorded in transmission mode through the membrane and the concentration of the phosphate is determined from the intensity of a band cantered at 700 nm. Using this method, the detection limit for phosphate in water is lowered to 0.64 μgL⁻¹. The approach has also been extended to detect arsenate in water with a detection limit of 4.8 μgL⁻¹ arsenate. . The method is also used to investigate real matrices with accuracy that matches the standard APHA method for detection of phosphate in water.

钼蓝法是美国公共卫生协会（APHA）批准的用于检测和定量水中磷酸盐的方法。标准的钼蓝方法APHA 4500 PE在带有5厘米比色皿的淡水中的检出限为30μgL ^-1磷酸盐（10μgL ^-1磷）。为了进一步将检测限降低至亚μgL ^-1在水平上，我们开发了一种简单，快速，无溶剂的方法，可将溶液中存在的磷酸盐转化为固体，以通过可见光谱进行定量。该方法通过用阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）进行电荷中和，将阴离子杂多钼酸根离子转化为固体胶体沉淀，然后将该沉淀捕获在可见透明膜上。然后以透射模式记录穿过膜的可见光谱，并根据在700 nm处倾斜的能带强度确定磷酸盐的浓度。使用该方法，水中磷酸盐的检出限降低到0.64μgL ^-1。该方法也已扩展到检测水中砷的检测极限，检测限为4.8μgL ^-1砷酸。。该方法还用于调查实际基质，其准确度与用于检测水中磷酸盐的标准APHA方法相匹配。