An extraction step is recommended for the lower levels of this range and when interferences must be over-come.Automated versions of the ascorbic acid method(F,G, and H) also are presented. Careful attention to procedure may allow application of these methods to very low levels of phosphorus, such as those found in unimpaired fresh-water systems. phos Ion chromatography(4110) and capillary ion electrophoresis (4140) are useful for determination of orthophosphate in undigested samples.