CN101782508A - Method for measuring contents of ferrous, ferric iron and total iron in seawater - Google Patents

Abstract

The invention relates to a simple and accurate method for determining the content of ferrous iron, ferric iron and total iron in seawater by using spectrophotometric technology. Fix the ferrous iron and ferric iron in the collected seawater samples, and adjust their pH to be slightly acidic; use phenanthrozine sodium salt solution as the color reagent, and make the blank control solution with the same salinity and pH as the water sample After the absorbance of the solution is set to zero, measure the absorbance of the standard solution and water sample; add hydroxylamine hydrochloride solution to the blank solution, standard solution and water sample to fully reduce the ferric iron in the water, add ammonium acetate buffer solution, and the blank control solution Set the absorbance to zero, measure the absorbance of the standard solution and the water sample; repeat the reduction step, add ammonium acetate buffer, set the absorbance of the blank control solution to zero, and measure the absorbance of the standard solution for the third time. Finally, the content of ferrous iron, ferric iron and total iron in seawater samples is calculated, which solves the application limitation of spectrophotometric technology in the determination of iron content in seawater.

Description

The assay method of ferrous in a kind of seawater, ferric iron and total iron content

Technical field

The present invention relates to spectrophotometry, specifically a kind of method of utilizing spectrophotometry to measure ferrous in the seawater, ferric iron and total iron content.

Background technology

Spectrophotometry is to utilize ultraviolet light, visible light, infrared light and laser etc. to measure the absorption spectrum of material, material is carried out the method for qualitative and quantitative analysis and structure of matter analysis by this absorption spectrum.The assay method commonly used of iron mainly comprises spectrophotometric method, atomic absorption method, inductance coupling plasma emission spectrum and mass spectroscopy, stripping voltammetry and chemoluminescence method etc. in the seawater.Traditional spectrophotometry mainly uses phenanthroline as developer, and it detects and is limited to 0.03mg/L, does not meet the relatively low situation of concentration of iron in the seawater.So when measuring seawater sample, need water sample is carried out pre-service, will measure after the iron enrichment, not only step is more loaded down with trivial details, and has increased the possibility that pollutes in the operation.Atomic absorption method and the sensitivity of inductance coupling process are higher, have higher accuracy, but also need sample is carried out preenrichment before analyzing, and is very loaded down with trivial details consuming time, and its instrument and equipment is relatively more expensive, has limited usable range.Stripping voltammetry and chemiluminescence determination cost are lower, instrument and equipment is simple, and detection limit is low, but the former mensuration process is more time-consuming, may be subjected to multiple factor affecting, and also difficulty and be difficult to measure the iron of organic complex attitude in the seawater relatively of the reagent purge process before the chemiluminescence determination.Therefore, need set up the assay method of different valence state iron content in the high seawater of a kind of simple and fast, stability and degree of accuracy, to adapt to the mensuration of iron in the seawater sample.

Summary of the invention

At the application limitations that classical spectrophotometry iron content in seawater is measured, the object of the present invention is to provide a whole set of to be applicable to the rapid and accurate determination method of ferrous in the different salinity seawater, ferric iron and total iron content.

Technical scheme of the present invention is as follows:

The assay method of ferrous in a kind of seawater, ferric iron and total iron content comprises the steps:

1) water sampling:

Gather water sample 10-100mL, add 1-2mol/L hydrochloric acid immediately, the volume ratio of hydrochloric acid and water sample is 1: (20-100), make the pH of water sample reach 1-2, as acidified water sample, sealing is preserved standby under the room temperature.

2) water sample is handled, and pH adjusts:

Add the 1-2mol/L sodium hydroxide solution to the step 1) gained in the water sample of acidifying, the volume ratio of sodium hydroxide solution and water sample is 1: (20-100), make water sample pH between 4-6, as water sample to be measured.

3) measure

3.1 colour developing:

Get blank solution, standard solution and each 1-5mL of water sample to be measured, add the 0.01-0.05mol/L luxuriant and rich with fragrance alloxazine one sodium salt (Ferrozine[3-(2-Pyridyl)-5 of 100-500 μ L with the preparation of 0.05-0.2mol/L ammonium acetate solution, 6-diphenyl-1,2,4-triazine-4 '; 4 "-disulfonic acid sodium salt], molecular formula: C ₂₀H ₁₃N ₄NaO ₆S ₂) solution, mixing.

Blank solution compound method is that preparation and the consistent sodium-chloride water solution of the initial salinity of water sample to be measured add 1-2mol/L hydrochloric acid again and make its pH between 4-6 earlier;

The standard solution compound method is to get the blank solution that pH has transferred to 4-6, adding FeCl ₃Making its total concentration of iron is 0.1-1mg/L;

Blank solution and standard solution are matching while using.

3.2 absorbance measurement for the first time:

Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, the absorbance A 1 of bioassay standard solution and water sample to be measured _Sample, A1 _Mark

3.3 reduction:

Get blank solution, standard solution and water sample to be measured after 0.8-4mL measures absorbance, add the oxammonium hydrochloride solution mixing of 150-750 μ L with the 1-2mol/L of 1-3mol/L hydrochloric acid preparation.After room temperature left standstill 5-10min, adding 50-250 μ L again was the 10mol/L ammonium acetate solution mixing of 9-10 with the pH of ammoniacal liquor preparation.

3.4 absorbance measurement for the second time:

Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, the absorbance A 2 of bioassay standard solution and water sample to be measured _Sample, A2 _Mark

3.5 absorbance measurement for the third time:

Repeating step 3.3.Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, bioassay standard solution absorbency A3 _Mark

4) ferrous, ferric iron and total concentration of iron calculate:

By total concentration of iron of standard solution and 3 absorbances of mensuration thereof, calculate ferrous and ferric absorptivity ε Fe (II), ε Fe (III) and α (A3 according to following formula earlier _Mark/ A2 _Mark), again in conjunction with 2 absorbances of water determination to be measured, utilize following formula to calculate ferrous (C in the seawater sample with this _{Fe (II)}), ferric iron (C _{Fe (III)}) and total iron (C _{Fe (t)}) concentration.

$C_{\mathrm{Fe}\left(\mathrm{II}\right)}=\frac{A_1{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}-A_2{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l}{{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}---\left(1\right)$

$C_{\mathrm{Fe}\left(\mathrm{III}\right)}=\frac{A_2-A_1\mathrm{\α}}{\mathrm{\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}---\left(2\right)$

C _Fe(t)＝C _Fe(II)+C _Fe(III) (3)

Above-mentioned formula is derived by following formula (4) and (5) and is obtained:

A ₁＝ε _Fe(II)lC _Fe(II)+ε _Fe(III)lC _Fe(III) (4)

A ₂＝ε _Fe(II)l(C _Fe(II)+C _Fe(III))α (5)

Because standard solution is the known FeCl of concentration ₃Solution, the concentration of Fe (II) are zero, so C when measuring absorbance 3.2 first time _{Fe (II)}=0, substitution formula (4) can calculate ε Fe (III)=A1 _Mark/ (lC _{Fe (III) mark});

Through 3.3 reduction steps, Fe in the standard solution (III) all is reduced to Fe (II), and the concentration of Fe (III) is zero, so when measuring absorbance 3.4 second time, C _{Fe (III)}=0, substitution formula (5) can calculate ε Fe (II)=A2 _Mark/ (lC _{Fe (II) mark}α)=A2 _Mark/ (lC _{Fe (III) mark}α)=A2 _Mark ²/ (lC _{Fe (III) mark}A3 _Mark);

In ε Fe (II), ε Fe (III) substitution formula (1)-(3), with this again in conjunction with 2 absorbance A 1 of water determination to be measured _Sample, A2 _Sample, can calculate ferrous (C in the seawater sample _{Fe (II)}), ferric iron (C _{Fe (III)}) and total iron (C _{Fe (t)}) concentration;

Wherein, l is the optical path of cuvette.

The principle of the invention is:

Spectrophotometry is to utilize material the absorption of light to be carried out the effective ways of qualitative or quantitative test to material, the present invention utilizes Lambert-Beer's law, and to be absorbance be directly proportional with the product of the thickness of the concentration of solution and liquid layer, measure the absorbance of the colourless solution of colored solutions or adding chromogenic reagent then, compare by solution absorbance of the same race, can calculate the concentration of material in the solution with concentration known.

Advantage of the present invention and good effect are as follows:

1, the present invention has improved existing water sample preprocess method, the water sample acidifying is regulated pH after preserving before mensuration, inciting somebody to action with the 1-2mol/L sodium hydroxide solution, the pH of acidified water sample is adjusted between the 4-6, make pH in the best color range of developer, measurement result is more accurate.

2, the present invention has considered the difference of institute's water sampling salinity, and blank solution is all consistent with water sample to be measured with the standard solution salinity.Blank solution and standard solution add sodium chloride makes salinity consistent with the institute water sampling, and adding 1-2mol/L hydrochloric acid, makes their pH the same with water sample to be measured, all is modulated between the 4-6.Thereby, reduced the influence of salinity to measurement result, can measure the water sample of different salinity.

3, the present invention uses luxuriant and rich with fragrance alloxazine one sodium salt as developer.It is complexing Fe (II) optionally, and it detects and is limited to 0.005mg/L, far below the detection limit of phenanthroline, is fit to the lower situation of iron content in the seawater.

4, the present invention considers the trickle influence that the Fe (III) in the water sample may cause testing result, and the absorbance of Fe (III) is counted, and makes the result more accurate.

Embodiment

That the present invention proposes is ferrous in a kind of seawater, the assay method of ferric iron and total iron content, at first ferrous, ferric iron in the seawater sample of gathering is fixed, and regulates its pH then to slant acidity.With luxuriant and rich with fragrance alloxazine one sodium salt solution as developer, after all consistent with the water sample blank solution absorbency of salinity, pH is set to zero, the absorbance of bioassay standard solution and water sample; Add oxammonium hydrochloride solution and make after ferric iron fully reduces in the water in above-mentioned blank solution, standard solution and water sample, add ammonium acetate buffer, the blank solution absorbency is set to zero again, then the absorbance of bioassay standard solution and water sample; Repeat step of reducing, also add ammonium acetate buffer, the blank solution absorbency is set to zero, then bioassay standard solution absorbency for the third time.Concentration by standard solution and 3 absorbances of mensuration thereof calculate the extension rate of ferrous and ferric absorptivity and water sample, calculate ferrous in the seawater sample, ferric iron and total iron content in conjunction with 2 absorbances of water determination again with this.

Below in conjunction with embodiment in detail the present invention is described in detail.

Embodiment 1

1) gather 30mL plant workshop water sample, add the 2mol/L hydrochloric acid of 1.5mL immediately, its pH is modulated to 1, as acidified water sample, sealing is preserved standby under the room temperature.

2) the 2mol/L sodium hydroxide solution of the about 1.5mL of adding in above-mentioned acidified water sample makes the pH of water sample reach 5, as water sample to be measured.

3) measure

At first prepare blank solution, standard solution.Blank solution compound method is prepare earlier and the consistent sodium-chloride water solution of the initial salinity of water sample to be measured, and adding 2mol/L hydrochloric acid to make its pH reach 5; The standard solution compound method is to get above-mentioned blank solution, to wherein adding FeCl ₃Making its total concentration of iron is 1mg/L.

3.1 colour developing:

Get blank solution, standard solution and each 1mL of water sample to be measured, add 0.01mol/L phenanthrene alloxazine one sodium salt solution of 100 μ L, mixing with the preparation of 0.1mol/L ammonium acetate solution.

3.2 absorbance measurement for the first time:

Under the 562nm wavelength, after the blank solution absorbency was set to zero earlier, the absorbance of bioassay standard solution and water sample to be measured was respectively: A1 _Sample=0.013, A1 _Mark=0.004.

3.3 reduction:

Take out blank solution, standard solution and water sample to be measured after 0.8mL measures absorbance, add the oxammonium hydrochloride solution mixing of 150 μ L with the 1mol/L of 2mol/L hydrochloric acid preparation.After room temperature leaves standstill 5min, add 50 μ L again and be 9.5 10mol/L ammonium acetate solution mixing with the pH of ammoniacal liquor preparation.

3.4 absorbance measurement for the second time:

Under the 562nm wavelength, after the blank solution absorbency was set to zero earlier, the absorbance of bioassay standard solution and water sample to be measured was respectively: A2 _Sample=0.045, A2 _Mark=0.368.

3.5 absorbance measurement for the third time:

Repeating step 3.3.Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, bioassay standard solution absorbency A3 _Mark=0.286.

4) ferrous, ferric iron and total concentration of iron calculate:

At first, by total concentration of iron of standard solution and 3 absorbances of mensuration thereof, calculate ferrous and ferric absorptivity ε Fe (II), ε Fe (III) and α (A3/A2) according to following formula earlier:

$C_{\mathrm{Fe}\left(\mathrm{II}\right)}=\frac{A_1{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}-A_2{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l}{{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

$C_{\mathrm{Fe}\left(\mathrm{III}\right)}=\frac{A_2-A_1\mathrm{\α}}{\mathrm{\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

C _Fe(t)＝C _Fe(II)+C _Fe(III)

In the present embodiment, ε Fe (II)=0.474 (L/molcm); ε Fe (III)=0.004 (L/molcm); α=0.777; L=1 (cm).

In conjunction with 2 absorbances of water determination to be measured, utilize above-mentioned formula to calculate the ferrous (C in the seawater sample that surveys again _{Fe (II)}), ferric iron (C _{Fe (III)}) and total iron (C _{Fe (t)}) concentration.

In the present embodiment, add the multiple that hydrochloric acid and sodium hydroxide solution make diluted sample when result of calculation is handled divided by water sample, ferrous, ferric iron concentration in this plant's workshop water sample are respectively 0.024mg/L and 0.087mg/L, and total concentration of iron is 0.111mg/L.

Embodiment 2

1) gather river deer island, 50mL Liaoning offshore water sample, add the 1mol/L hydrochloric acid of 0.5mL immediately, its pH is modulated to 2, as acidified water sample, sealing is preserved standby under the room temperature.

2) the lmol/L sodium hydroxide solution of the about 0.5mL of adding in above-mentioned acidified water sample makes the pH of water sample reach 4, as water sample to be measured.

3) measure

At first prepare blank solution, standard solution.Blank solution compound method is prepare earlier and the consistent sodium-chloride water solution of the initial salinity of water sample to be measured, and adding 2mol/L hydrochloric acid to make its pH reach 4; The standard solution compound method is to get above-mentioned blank solution, to wherein adding FeCl ₃Making its total concentration of iron is 1mg/L.

3.1 colour developing:

Get blank solution, standard solution and each 3mL of water sample to be measured, add 0.02mol/L phenanthrene alloxazine one sodium salt solution of 300 μ L, mixing with the preparation of 0.1mol/L ammonium acetate solution.

3.2 absorbance measurement for the first time:

Under the 562nm wavelength, after the blank solution absorbency was set to zero earlier, the absorbance of bioassay standard solution and water sample to be measured was respectively: A1 _Sample=0.021, A1 _Mark=0.003.

3.3 reduction:

Take out blank solution, standard solution and water sample to be measured after 2.6mL measures absorbance, add the oxammonium hydrochloride solution mixing of 300 μ L with the 2mol/L of 2mol/L hydrochloric acid preparation.After room temperature leaves standstill 10min, add 100 μ L again and be 9.5 10mol/L ammonium acetate solution mixing with the pH of ammoniacal liquor preparation.

3.4 absorbance measurement for the second time:

Under the 562nm wavelength, after the blank solution absorbency was set to zero earlier, the absorbance of bioassay standard solution and water sample to be measured was respectively: A2 _Sample=0.060, A2 _Mark=0.370.

3.5 absorbance measurement for the third time:

Repeating step 3.3.Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, bioassay standard solution absorbency A3 _Mark=0.289.

4) ferrous, ferric iron and total concentration of iron calculate:

At first, by total concentration of iron of standard solution and 3 absorbances of mensuration thereof, calculate ferrous and ferric absorptivity ε Fe (II), ε Fe (III) and α (A3/A2) according to following formula earlier:

$C_{\mathrm{Fe}\left(\mathrm{II}\right)}=\frac{A_1{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}-A_2{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l}{{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

$C_{\mathrm{Fe}\left(\mathrm{III}\right)}=\frac{A_2-A_1\mathrm{\α}}{\mathrm{\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

C _Fe(t)＝C _Fe(II)+C _Fe(III)

In the present embodiment, ε Fe (II)=0.474 (L/molcm); ε Fe (III)=0.003 (L/molcm); α (A3/A2)=0.781; L=1 (cm).

In conjunction with 2 absorbances of water determination to be measured, utilize above-mentioned formula to calculate the ferrous (C in the seawater sample that surveys again _{Fe (II)}), ferric iron (C _{Fe (III)}) and total iron (C _{Fe (t)}) concentration.

Add hydrochloric acid and sodium hydroxide solution when result of calculation is handled divided by water sample and make the multiple of diluted sample, calculate ferrous in this offshore water sample, ferric iron concentration and be respectively 0.040mg/L and 0.109mg/L, total concentration of iron is 0.149mg/L.

Embodiment 3

1) gather 15mL Huanghai Sea marine site water sample, add the 2mol/L hydrochloric acid of 0.3mL immediately, its pH is modulated to 1.4, as acidified water sample, sealing is preserved standby under the room temperature.

2) the 2mol/L sodium hydroxide solution of the about 0.3mL of adding in above-mentioned acidified water sample makes the pH of water sample reach 6, as water sample to be measured.

3) measure

At first prepare blank solution, standard solution.Blank solution compound method is prepare earlier and the consistent sodium-chloride water solution of the initial salinity of water sample to be measured, and adding 2mol/L hydrochloric acid to make its pH reach 4; The standard solution compound method is to get above-mentioned blank solution, to wherein adding FeCl ₃Making its total concentration of iron is 1mg/L.

3.1 colour developing:

Get blank solution, standard solution and each 1.8mL of water sample to be measured, add 0.01mol/L phenanthrene alloxazine one sodium salt solution of 200 μ L, mixing with the preparation of 0.1mol/L ammonium acetate solution.

3.2 absorbance measurement for the first time:

Under the 562nm wavelength, after the blank solution absorbency was set to zero earlier, the absorbance of bioassay standard solution and water sample to be measured was respectively: A1 _Sample=0.091, A1 _Mark=0.007.

3.3 reduction:

Take out blank solution, standard solution and water sample to be measured after 1.8mL measures absorbance, add the oxammonium hydrochloride solution mixing of 150 μ L with the 1mol/L of 2mol/L hydrochloric acid preparation.After room temperature leaves standstill 10min, add 50 μ L again and be 9.5 10mol/L ammonium acetate solution mixing with the pH of ammoniacal liquor preparation.

3.4 absorbance measurement for the second time:

Under the 562nm wavelength, after the blank solution absorbency was set to zero earlier, the absorbance of bioassay standard solution and water sample to be measured was respectively: A2 _Sample=0.139, A2 _Mark=0.375.

3.5 absorbance measurement for the third time:

Repeating step 3.3.Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, bioassay standard solution absorbency A3 _Mark=0.290.

4) ferrous, ferric iron and total concentration of iron calculate:

At first, by total concentration of iron of standard solution and 3 absorbances of mensuration thereof, calculate ferrous and ferric absorptivity ε Fe (II), ε Fe (III) and α (A3/A2) according to following formula earlier:

$C_{\mathrm{Fe}\left(\mathrm{II}\right)}=\frac{A_1{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}-A_2{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l}{{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

$C_{\mathrm{Fe}\left(\mathrm{III}\right)}=\frac{A_2-A_1\mathrm{\α}}{\mathrm{\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

C _Fe(t)＝C _Fe(II)+C _Fe(III)

In the present embodiment, ε Fe (II)=0.485 (L/molcm); ε Fe (III)=0.007 (L/molcm); α (A3/A2)=0.773; L=1 (cm).

In conjunction with 2 absorbances of water determination to be measured, utilize above-mentioned formula to calculate ferrous (C in the seawater sample again _{Fe (II)}), ferric iron (C _{Fe (III)}) and total iron (C _{Fe (t)}) concentration.

Calculate ferrous in this marine site water sample, ferric iron concentration and be respectively 0.154mg/L and 0.155mg/L, total concentration of iron is 0.309mg/L.

The result shows that operating process of the present invention is simply quick, and precision height, good reproducibility, detection limit are low as a result, can be used for ferrous in the different waters seawater sample, ferric iron and Rapid Determination of Total Iron, and its scope of application is extensive.

Claims (1)

1. the assay method of ferrous in the seawater, ferric iron and total iron content is characterized in that concrete steps are as follows:

1. gather the 10-100mL water sample, add 1-2mol/L hydrochloric acid immediately, the volume ratio of hydrochloric acid and water sample is 1: (20-100), make water sample pH to 1-2, and as acidified water sample, sealing, standby under the room temperature;

2. to step 1. gained in the water sample of acidifying, add the 1-2mol/L sodium hydroxide solution, the volume ratio of sodium hydroxide solution and water sample is 1: (20-100), make water sample pH between 4-6, as water sample to be measured;

3. in the standard solution of 1-5mL blank solution, concentration known and water sample to be measured, add 100-500 μ L respectively with the luxuriant and rich with fragrance alloxazine one sodium salt solution colour developing of the 0.01-0.05mol/L of 0.05-0.2mol/L ammonium acetate solution preparation; Wherein, blank solution compound method is that preparation and the consistent sodium-chloride water solution of the initial salinity of water sample to be measured add 1-2mol/L hydrochloric acid again and make its pH between 4-6 earlier; The standard solution compound method of concentration known is to get the blank solution that pH has transferred to 4-6, adding FeCl ₃Making its total concentration of iron is 0.1-1mg/L;

4. under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, the absorbance A 1 of bioassay standard solution and water sample to be measured _Sample, A1 _Mark

5. get blank solution, standard solution and water sample to be measured after 0.8-4mL measures absorbance, add the oxammonium hydrochloride solution mixing of 150-750 μ L with the 1-2mol/L of 1-3mol/L hydrochloric acid preparation; After room temperature left standstill 5-10min, adding 50-250 μ L again was the 10mol/L ammonium acetate solution mixing of 9-10 with the pH of ammoniacal liquor preparation;

6. under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, the absorbance A 2 of bioassay standard solution and water sample to be measured _Sample, A2 _Mark

7. repeating step 5.; Under the 562nm wavelength, after the blank solution absorbency is set to zero earlier, bioassay standard solution absorbency A3 _Mark

8. ferrous, ferric iron and total concentration of iron calculate, earlier calculate ferrous and ferric absorptivity ε Fe (II), ε Fe (III) and α by total concentration of iron of standard solution and 3 absorbances of mensuration thereof according to following formula, α=A3/A2 utilizes following formula to calculate ferrous C in the seawater sample in conjunction with 2 absorbances of water determination with this again _{Fe (II)}, ferric iron C _{Fe (III)}And total iron C _{Fe (t)}Concentration;

$C_{\mathrm{Fe}\left(\mathrm{II}\right)}=\frac{A_1{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}-A_2{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l}{{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}\mathrm{l\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

$C_{\mathrm{Fe}\left(\mathrm{III}\right)}=\frac{A_2-A_1\mathrm{\α}}{\mathrm{\α}({\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{II}\right)}l-{\mathrm{\ϵ}}_{\mathrm{Fe}\left(\mathrm{III}\right)}l)}$

C _Fe(t)＝C _Fe(II)+C _Fe(III)

Wherein, l is the optical path of cuvette.