JPS5991367A - Highly sensitive analysis of phosphate ion - Google Patents

Abstract

PURPOSE:To achieve a quick and accurate analysis with the measurement of hourly changes in the absorbance due to a coloring reaction by instantaneously mixing a mixture of a trace quantity of phosphate ion dissolved aqueous solution and an acid sulfuric molybdate solution with a coloring liquid in a cell of a stop flow spectrophotometer. CONSTITUTION:A solution A of mixing a sample aqueous solution containing a trace quantity of PO4 ion and an acid sulfuric molybdenate ammonium aqueous solution and a solution (coloring liquid B) of ammonium molybdenate, concentrated sulfuric acid and malachite green are prepared. Then, the solution A and the coloring solution B are mixed quickly in a cell of a stop flow spectrophotometer to form color and absorption changes of a 650nm light are tracked to measure a variation of the absorbance DELTAA until the absorbance increases gradually from the first rising. As the value DELTAA is in the linear relationship with the PO4 ion concentration, the calibration curve which was determined using a PO4 solution with a known concentration is used to enable the measurement with a high sensitivity 5-10 times greater than before only requiring about 20sec.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved highly sensitive analytical method for phosphate ions.

In recent years, the increase in phosphoric acid components flowing into rivers, lakes, inland seas, etc. has caused the proliferation of algae, etc., and the need to strengthen monitoring systems for phosphoric acid components in these water bodies and inflow water sources is becoming a social issue. .

However, the concentration of phosphate ions in these places is generally extremely low, and until now there has been no way to analyze it directly. It was only possible to raise the detection limit for analysis, which required complicated operations and time.

The method of the present invention compensates for the shortcomings of the conventional method, does not require complicated preconcentration operations, and uses a simple method to reduce dissolved orthophosphate ions to 2.5 PPM (equivalent to 5 to 10 times as much as the conventional method). ) succeeded in directly analyzing the stock solution with high sensitivity.

In the method for analyzing phosphate ions according to the present invention, a reaction that exhibits a sensitive coloring property for phosphate ions was selected;
By completing the phosphorus-molybdic acid formation reaction in Solution A in advance, we were able to speed up the color development reaction by approximately 10 times. Using a stopped-flow spectrophotometer, we observed the time change in color development while the mixture was still. Due to the synergistic effect of various effects such as the adoption of a time-difference analysis method that allows for highly sensitive measurements without noise due to cell and liquid movement, etc., the detection sensitivity is several times higher than that of conventional methods. was completed.

The method of the present invention will be specifically explained below using examples. Although this example is an example in which the stock solution was directly analyzed, the method of the present invention can also be performed by combining appropriate preconcentration operations such as evaporation concentration method, extraction concentration method, ion concentration method using reverse permeation membrane method, etc. Furthermore, the detection limit can be increased by about 3 to 5 times.

Examples (Reagents) 1) Phosphorus standard solution A standard solution was prepared using potassium diphosphate. ii) Sulfuric acid acidic molybdic acid solution: 0
．． Add 25ml of concentrated sulfuric acid to 60rr+/33M ammonium molybdate and make up to 100ml with water. 1ii
) Color developer: 0.33 M ammonium molybdate 3
oml S concentrated sulfur e12.5ml and 0.002M
Mix 25ml of V Sikaite Green and add 200ml of water.
ml. After allowing it to stand for about 1 hour, separate the insoluble matter and use it.

(Operation) Add 2.5 ml of sulfuric acid molybdic acid solution to 7.5 ml of phosphorus standard solution, shake well, and leave for 15 minutes. Stopped flow apparatus (Union Giken 5F-
70), and add 10 m7 of coloring liquid to the other.
and rapidly mix both solutions and react at room temperature (approximately 25°C). The response is followed by absorption change at 650 mm.

(Result) By completing the formation reaction of phosphomolybdic acid in advance, the color development speed can be made faster (about 10 times) than when the coloring solution is directly applied to phosphorus. Although a reproducible reaction curve is obtained, the curve exhibits a sigmoidal shape as shown in FIG. 1, suggesting the complexity of the reaction process. Further, after the initial rise in the absorbance for several seconds to several tens of seconds, the absorbance continues to gradually increase over a long period of time (at least 20 minutes or more), making it difficult to determine the end point. Therefore, we obtained a reaction curve until the absorbance gradually increases (
At a phosphorus concentration of a few PPB, it takes about 2
It takes 0 seconds. ), the gradual increase portion is extrapolated to the time zero axis as shown by the broken line in the figure, and the amount of change (ΔA) is determined from the intersection with the axis. An example of a calibration curve obtained from the amount of change determined in this manner is shown in FIG. By repeating the signal integration five times or more, the concentration of the test solution is 2.7 PP.
It was found that phosphorus in B was also detectable.

[Brief explanation of drawings]

The figure shows an example of phosphate ion analysis using the method of the present invention.
The figure shows the elapsed time when coloring a solution with a phosphorus concentration of 13.5 PPB, and Figure 2 shows the relationship between these and the amount of change (ΔA) when the phosphoric acid concentration is varied. It is a graph. Suspension L1 Ko and the curved shavings (Rinshi clothes degree -13,5 PPT3's 4th session) +0 20
30 40 50 6. b 21 ￥l piece f θJ

Claims (1)

[Claims] (1) A mixture of an aqueous solution containing a trace amount of phosphate ion and a sulfuric acid acidic molybdic acid solution (liquid A), and a sulfuric acid acidic malachite green solution containing molybdic acid prepared separately from this (liquid B), A highly sensitive analysis method for phosphate ions that is instantaneously mixed in the cell of a stopped-flow spectrophotometer and measures the change in absorbance over time due to a color reaction.