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磷的比色测定,一般有钼兰法和钒钼黄法。钼兰法根据还原剂的不同,又可分为数种。以氯化亚锡为还原剂的钼兰法应用较为普遍,此法灵敏度高,但颜色稳定时间短,对酸系统和酸浓度要求较严格,铁等干扰离子的影响较大。有人推荐以抗坏血酸为还原剂,可使颜色稳定24小时,亦能防止铁的干扰,但此法显色较慢,须加温促其显色。钒钼黄法颜色稳定,不需还原剂,干扰离子少,酸度适应范围较广,但灵敏度低,大约为钼兰法的十分之一。近几年,国外广为推荐钼酸铵～酒石酸锑钾～抗坏血酸混合试剂法(以下简称铝锑抗法),此法显色快,颜色稳定,灵敏度高,对干扰离子的允许量较大,有较宽的酸度适应范围,用于土壤农化分析,可适用于各种不同的待测液。加入酒石酸锑钾可加速显色,并对干扰离子起掩蔽作用,使颜色稳定。
Phosphorus colorimetric determination, generally Molylan law and vanadium molybdenum yellow method. Molybdenum law according to the different reductant can be divided into several species. The molybdenum blue method with stannous chloride as reductant is more common. The method has high sensitivity, but the color stability time is short, the requirements on the acid system and acid concentration are more stringent, and the influence of iron and other interfering ions is greater. It is recommended ascorbic acid as a reducing agent, the color can be stable for 24 hours, but also to prevent the interference of iron, but the color of this method is slower, to be heated to promote its color. Vanadium molybdenum yellow color stability, no reducing agent, less interference ions, acidity to adapt to a wider range, but the sensitivity is low, about one-tenth of the molybdenum blue method. In recent years, foreign widely recommended ammonium molybdate ~ antimony aspartate tartrate ~ ascorbic acid mixed reagent method (hereinafter referred to as aluminum antimony method), this method fast color, color stability, high sensitivity, the larger the allowable amount of interfering ions, A wide range of acidity adaptation for soil analysis of agriculture, can be applied to a variety of different test solution. Adding antimony potassium tartrate accelerates color development and masks the interfering ions to stabilize the color.