CN1264041A - Method for eliminating Fe2+ interference in detection of Zn content - Google Patents

Abstract

A method for eliminating the Fe2+ ions interference in adetermining Zn content in the mixture of zinc sulfate and ferrous sulfate includes such steps as using 3% H2O2 to oxidize Fe2+ into Fe3+, heating to remove excess H2O2, dripping 20% H2SO4 solution to remove precipitate, using NaF solution to shielf Fe3+, using standard EDTA titration solution in weak-acidic solution where pH is 5.5 and xylenol orange is used as indicator to titrate, and calculating zinc content based on the loss of EDTA.

Description

Fe in Zn content measurement2+Interference elimination method

The invention relates to Zn and Fe²⁺A method for measuring Zn in the mixture, in particular to Fe in the measurement of Zn content²⁺A method for eliminating interference.

The method for measuring the zinc content in the zinc sulfate by adopting the EDTA complexation titration method is a classical chemical analysis method, has high accuracy and obvious change of the end point color, so the method is widely applied to the standards of industrial and agricultural zinc sulfate at home and abroadThe method is widely used. Chemical literature indicates that EDTA and Zn²⁺And Fe²⁺The stability constants of the complexes were 16.49 and 14.32, respectively, very close and EDTA titrated Zn²⁺And Fe²⁺With minimum pH values of 4.0 and 4.5, respectively, xylenol orange is suitable for complexometric titration in acidic solutions with pH<6, changing the color from magenta to lemon yellow. Therefore, Zn can be titrated simultaneously by EDTA in a weakly acidic solution (pH 5-6) and xylenol orange as an indicator²⁺And Fe²⁺. Because ferrous sulfate is not associated in the production process of zinc sulfate, Fe is not considered in the existing chemical analysis method²⁺Interference of (1), Fe described in the chemical literature²⁺Cannot be used in the process (e.g. phenanthroline with Fe)²⁺A reddish brown chelate is formed, interfering with the observation of the endpoint). If the sample contains Fe²⁺Then is Fe²⁺Is coated with Zn²⁺Is detected, the finally calculated zinc content is actually Zn²⁺With Fe²⁺And (4) summing.

The invention aims to overcome the defects of the prior art and provide a Fe-free Fe-containing alloy capable of solving the problem of Fe²⁺Solves the problem that the existing chemical analysis method can not detect Zn²⁺With Fe²⁺The true zinc content of the mixture.

Fe in Zn content measurement according to the present invention²⁺The interference elimination method adopts 3 percent of H for the mixture of zinc sulfate and ferrous sulfate₂O₂Oxidation of Fe²⁺To Fe³⁺Heating to remove excess H₂O₂Dropwise adding 20% of H₂SO₄Removing precipitate generated during heating process, and shielding Fe with NaF solution³⁺Using xylenol orange as an indicator, titrating by using an EDTA standard titration solution in a weak acid solution with the pH value of about 5.5, and calculating the content of zinc sulfate in the mixture according to the volume of consumed EDTA. Can also be said to use H₂O₂Oxidation of Fe²⁺To Fe³⁺Then shielding Fe with NaF solution³⁺Method of eliminating Fe²⁺The interference of (2). The specific operation method is as follows: weigh 4.0 to 4.5 g Fe²⁺And Zn²⁺A sample of the mixture was dissolved and made to a volume of 250 ml, then 25 ml of the solution was aspirated into a 250 ml beaker, and 2.0 ml of 3% aqueous hydrogen peroxide was added (theoretically all samples were FeSO)₄.7H₂When O is used, only 0.9 ml is needed for complete oxidation, in the method, 2.0 ml of the catalyst is added in excess for complete oxidation, and then heated on an electric furnace to boil and held for 2 minutes (in this case, H)₂O₂Has been completely decomposed if H₂O₂The incomplete decomposition reacts with a shielding agent KI added later to generate reddish brown I₂And the observation of the end point is disturbed, ) Due to H₂O₂OH is produced upon decomposition^-Production of Fe (OH)₃Precipitating to make the solution turbid, and adding 20% H dropwise₂SO₄The solution was made clear, diluted to 100 ml with water, 20 ml of 10% sodium fluoride solution and 1 g potassium iodide were added, then 2 drops of xylenol orange indicator solution were added, and hexamethylenetetramine solution was added dropwiseWhen the solution is carmine, 10 ml of acetic acid and sodium acetate buffer solution are added, the EDTA standard solution is used for titration, and the end point is that the solution is changed from carmine to lemon yellow (the experiment proves that for Zn, the end point is²⁺、Fe²⁺When the content of ferrous sulfate in the mixture exceeds 50 percent, 2.0 g of NH is added₄F, particularly after adding acetic acid and sodium acetate buffer solution, easily makes the solution cloudy, so that, by using NaF instead, the shielding effect is consistent and colorless FeF is formed₆ ^3-And no turbidity is produced).

Fe is determined by adopting the Zn content of the invention²⁺Interference elimination method for measuring Fe²⁺And Zn²⁺The true zinc content in the mixture can eliminate Fe²⁺Solves the problem that the existing chemical analysis method can not detect Zn²⁺With Fe²⁺The true zinc content of the mixture.

According to the technical scheme of the invention, the embodiment is provided as follows: weighing 4.0-4.5 g Fe²⁺And Zn²⁺A sample of the mixture was dissolved and made to a volume of 250 ml, then 25 ml of the solution was aspirated into a 250 ml beaker, and 2.0 ml of 3% aqueous hydrogen peroxide was added (theoretically all samples were FeSO)₄.7H₂When O is used, only 0.9 ml is needed for complete oxidation, in the method, 2.0 ml of the catalyst is added in excess for complete oxidation, and then heated on an electric furnace to boil and held for 2 minutes (in this case, H)₂O₂Has been completely decomposed if H₂O₂The incomplete decomposition reacts with a shielding agent KI added later to generate reddish brown I₂And the observation of the end point is disturbed, ) Due to H₂O₂OH is produced upon decomposition^-Production of Fe (OH)₃Precipitating to make the solution turbid, and adding 20% H dropwise₂SO₄Making the solution transparent, diluting to 100 ml with water, adding 20 ml of 10% sodium fluoride solution and 1 g of potassium iodide, then adding 2 drops of xylenol orange indicator solution, adding dropwise hexamethylene tetramine solution until carmine appears, adding 10 ml of acetic acid and sodium acetate buffer solution, titrating with EDTA standard solution, and obtaining the end point when the solution changes from carmine to lemon yellow (experiment proves that for Zn, the end point is that²⁺、Fe²⁺When the content of ferrous sulfate in the mixture exceeds 50 percent, 2.0 g of NH is added₄F, particularly after adding acetic acid and sodium acetate buffer solution, easily makes the solution cloudy, so that, by using NaF instead, the shielding effect is consistent and colorless FeF is formed₆ ^3-And no turbidity is produced).

Claims (1)

1. Fe in Zn content measurement²⁺The interference eliminating method includes using xylenol orange as indicator liquid, titrating in weak acid solution of pH 5.5 with EDTA standardtitration solution, calculating the zinc sulfate content in the mixture based on the EDTA consumption volume, and adopting 3% H for the mixture of zinc sulfate and ferrous sulfate₂O₂Oxidation of Fe²⁺To Fe³⁺Heating to remove excess H₂O₂Dropwise adding 20% of H₂SO₄Removing precipitate generated during heating process, and shielding Fe with NaF solution³⁺。