CN104155260A - Method for directly measuring major sulfate radical by using ultraviolet spectrophotometry - Google Patents

Abstract

The invention discloses a kind of methods that constant sulfate radical is directly measured using ultraviolet spectrophotometry, desulfurized gypsum is weighed in beaker, dense HCl is added, with pure distilled water, it is dissolved under magnetic stirrer, BaCl2 is added, stirring stands after precipitating BaSO4 sufficiently, is all transferred in centrifuge tube, it is centrifuged on centrifuge, washing separation repeatedly, until inspection nothing left Cl-1, supernatant discard; Na3PO4 is added in BaSO4 precipitating again, stirs and evenly mixs standing, makes All after dissolution, it is all transferred to centrifuge tube together with water lotion, all supernatant dilution constant volumes are taken after centrifuge separation; Absorbance A is measured respectively at ultraviolet band 193nm and 210nm, is obtained with the mode of solution binary linearity Simultaneous Equations by computer Excel program solution Concentration. The method of the present invention has speed quick, and step is simple, and instrument class is of less demanding, the advantages such as relatively high to major constituents sample analysis accuracy.

Description

Adopt ultraviolet spectrophotometry directly to measure the method for constant sulfate radical

Technical field

The present invention relates to a kind of method that adopts ultraviolet spectrophotometry directly to measure constant sulfate radical.

Background technology

The mensuration of sulfate radical is always with indirect mode, by the whole bag of tricks, incites somebody to action negative ion is transformed into another form, then measures the related data of these forms, finally extrapolates the amount of sulfate radical.As gravimetric method, volumetric precipitation method, spectrophotometric method, conductometry, ion selective electrode method etc.Outside deionization chromatogram, directly measure negative ion method less.As everyone knows, the classical analysis method of sulfate radical is barium sulphate gravimetric method, and this method is with a long history, and accuracy is high, remains so far the pedestal method of stipulating in multiple GB.But the steps such as the filtration of gravimetric method, washing, calcination, precipitation, constant weight are time-consuming, loaded down with trivial details, easily error of operation.

Summary of the invention

The object of the present invention is to provide a kind of method easy, adopt ultraviolet spectrophotometry directly to measure the method for constant sulfate radical accurately.

Technical solution of the present invention is:

A kind of method that adopts ultraviolet spectrophotometry directly to measure constant sulfate radical, it is characterized in that: for the sample desulfurated plaster that has certain interfering material: accurately take desulfurated plaster 0.0800～0.0900g in beaker, add the dense HCl of 0.50ml, to be no less than the pure distilled water of 50ml, at 40 ℃, under 10min magnetic stirrer, dissolve, add 3.00 * 10-2molL-1 BaCl225.00ml, after stirring the standing BaSO4 of making and fully precipitating, all be transferred in centrifuge tube, centrifugal 15min on 2500r/min hydro-extractor, separated three times of cyclic washing, to examining nothing left Cl-1, supernatant all discards, in BaSO4 precipitation, add 2.0 * 10-2molL-1Na again ₃pO ₄15.00ml, stirs and evenly mixs standingly, makes all, after stripping, together with water lotion, all proceed to centrifuge tube, after centrifuging, get all supernatant dilutions and be settled to 1000ml, at ultraviolet band 193nm and 210nm place, measure respectively absorbance A, by the mode of separating binary linearity Simultaneous Equations, by computing machine Excel program solution, obtain concentration.

Described binary linearity Simultaneous Equations is when precipitating for the second time, after adding, with form two Component Systems, Simultaneous Equations is:

$\left\{\begin{array}{cc}{A}_{193}^{{\mathrm{SO}}_4^{2-}+{\mathrm{PO}}_4^{3-}}=728.8\×C_{{\mathrm{SO}}_4^{2-}}+2707\×C_{{\mathrm{PO}}_4^{3-}}& \left(1\right)\\ A_{210}^{{\mathrm{SO}}_4^{2-}+{\mathrm{PO}}_4^{3-}}=82.50\×C_{{\mathrm{SO}}_4^{2-}}+112.5\×C_{{\mathrm{PO}}_4^{3-}}& \left(2\right)\end{array}\right.$

concentration can try to achieve by computing machine Excel program; Wherein:

be respectively the absorbance recording at ultraviolet band 193nm and 210nm place; for concentration; for concentration.

It is quick that the inventive method has speed, and step is simple, and instrument class is less demanding, to the more high advantage of major constituents sample analysis accuracy.Method is applied to the mensuration of calcium sulphate in thermal power plant's flue desulfurization gypsum, and data and gravimetric method are substantially identical.This method is directly measured sulfate radical with easy ultraviolet-visible spectrophotometer in heavy contend analysis, thereby can replace loaded down with trivial details barium sulphate gravimetric method.

Accompanying drawing explanation

Below in conjunction with drawings and Examples, the invention will be further described.

Fig. 1 is uv absorption spectra.

Embodiment

1.1 instruments and reagent

General general TU-1901 type, T10 type twin-beam ultraviolet-visible pectrophotometer, Shimadzu Auy220 electronic analytical balance, the TDL-40B of Anting Scientific Instrument Factory, Shanghai hydro-extractor, the Shanghai SG2-5-12 of the experimental electric furnace factory crucible electrical resistance furnace of analysing.

Reagent: 3.00 * 10-2molL-1 BaCl2, solution, 2.0 * 10-2molL-1 Na3PO4 solution, analyzes pure level inorganic oxygen-containing acid sodium-salt, various mineral sulfates.

1.2 test method

For main content, at more than 95% mineral sulfates, need only interfering material few, can be directly water-soluble, take standard specimen as measuring with reference to upper machine.

For the sample that has certain interfering material, this experiment be take desulfurated plaster as example: accurately take 0.0800～0.0900g in small beaker, add the dense HCl of 0.50ml, to be no less than the high-purity distilled water of 50ml, under 40 ℃, 10min magnetic stirrer, dissolve, add 3.00 * 10-2molL-1 BaCl225.00ml, after stirring the standing BaSO4 of making and fully precipitating, all be transferred in centrifuge tube, centrifugal 15min on 2500r/min hydro-extractor, separated three times of cyclic washing, to examining nothing left Cl-1, supernatant all discards.In BaSO4 precipitation, add 2.0 * 10-2molL-1 Na3PO415.00ml again, stir and evenly mix standingly, make all, after stripping, together with water lotion, all proceed to centrifuge tube, after centrifuging, get all supernatant dilutions and be settled to 1000ml.At ultraviolet band 193 and 210nm place, measure respectively absorbance A, by the mode of separating binary linearity Simultaneous Equations, pass through computing machine Excel program solution concentration.

2 results and discussion

2.1 absorption spectrum

Utilize and generally analyse general TU-1901 type twin-beam ultraviolet-visible pectrophotometer 0.04molL-1 metabisulfite solution is carried out to spectral scan, find has absorption below 210nm, and spectrogram is as follows

In figure, curve 1, and the sulfate radical of TU-1901 type Instrument measuring has absorption peak at 193nm, considers that the mensuration lower limit of TU-1901 type instrument is 190nm, and figure may be limit by instrument performance.So again by the general T10 type twin-beam ultraviolet-visible pectrophotometer that is limited to 180nm under the general nitrogen atmosphere of recently releasing, mensuration of analysing, carry out the following deep ultraviolet wave band scanning of 190nm.Curve 2 explanations, the λ max of sulfate radical is positioned at 185nm, and absorbance is stronger.This experiment can complete more than 190nm, so all data still adopt relatively more universal and inexpensive TU-1901 type Instrument measuring at present.

The uv absorption phenomenon of 2.2 common inorganic oxygen-containing acid groups

The uv absorption of inorganic salts, rarely has report.Consult various textbooks, handbook, reference book, all only discuss organic ultraviolet spectrum and assay method.Experiment is carried out uv scan to common inorganic oxysalt, and data are as follows:

The common inorganic oxygen-containing acid sodium-salt of table 1. ultra-violet absorption spectrum

As can be seen from Table 1: 1. inorganic oxygen-containing acid group has uv absorption, λ max is in 200nm left and right; 2. the molar absorption coefficient of inorganic oxygen-containing acid group is generally less, and to differ approximately two orders of magnitude even more with most of organic highly sensitive uv absorption; 3. molar absorption coefficient is relatively large negative ion, ε can reach 10 ³more than the order of magnitude, this may with its sp ²hydridization, Ion configuration is plane triangle, as long as less energy UV radiation can cause that larger absorption is relevant.On analyzing because sensitivity is higher, ultraviolet spectral analysis be used widely ^[8,9]; 4. deng sp ³hydridization, be configured as positive tetrahedron granule shape positive tetrahedron negative ion when ultraviolet ray is irradiated, must have larger energy, just can cause that associated electrical excites, so absorbing wavelength is shorter, ε is less.

2.3 common sulfate ultra-violet absorption spectrums

The ultra-violet absorption spectrum of the common colourless inorganic sulfate of table 2.

According to table 2 data, can judge: 1. the uv absorption of colourless sulfate in aqueous solution belongs to weak absorption, can think by n → σ ^*and n → π ^*cause, belong to R absorption band.2. λ max is below 200nm, and ε is all below 100, and molar absorption coefficient ε is little.3. be all sulfate, λ _maxall there is fine difference with ε, can only think relevant with cationic kind.So the similarities and differences of metallic ion have minor impact to sulfate ε.

2.4 test conditions are selected

2.4.1 the selection of solvent

Because nitric acid, sulfuric acid, these three kinds of common solvent acid of hydrochloric acid all contain the anionic group that tool ultraviolet region absorbs, according to table 1, can find out, nitric acid there is ultraviolet region to absorb by force, sulfuric acid can bring common-ion effcet to be also not suitable for, the Cl of hydrochloric acid ^-less absorption.So nitric acid, sulfuric acid are not suitable for doing the solvent acid of desulfurated plaster sample.Organic solvent methyl alcohol, ethanol etc. all have uv absorption, therefore with hydrochloric acid and high-purity water as solvent.Select water to make solvent, committed step is will be contained in two quartz colorimetric utensils and correct baseline with pure water before instrument scanning.Blank baseline must be horizontal linear, so just can offset the absorption of water.

2.4.2 the control of temperature

Look into handbook ^[10]know CaSO ₄in the time of 10～40 ℃, solubleness is 0.1928～0.2097g/100ml, so get the sample of 0.0861g, reference literature ^[11]be dissolved in the warm water of approximately 40 ℃ of 50ml, through 20min, stir, can guarantee that in sample, calcium sulphate all dissolves.

2.4.3 the control of acidity

Barium sulfate precipitate requires the weak acidic medium of pH4 left and right, simultaneously for eliminating interference, therefore adopt the dense HCl of 0.5ml, make Ba ²⁺with in suitable acidity medium, precipitate completely.By 3 centrifugation, separating, washing, and with AgNO ₃detect to nothing left Cl ^-1.

2.4.4 BaCl ₂addition

Primary sedimentation Ba in this experiment ²⁺amount must be more than or equal to amount, through experiment repeatedly, determine and to add 25mL0.03molL ^-1baCl ₂guarantee sulfate radical precipitation is complete, and inexcessive too many again.Excessive Ba ²⁺and Cl ^-1when follow-up centrifuging, discard.

2.4.5 Na ₃pO ₄addition

Precipitated for making again discharge, utilize Ba ₃(PO ₄) ₂k _spbe 3.4 * 10 ^-23compare BaSO ₄k _sp1.1 * 10 ^-10less feature, adds secondary precipitate agent Na ₃pO ₄, test determines that adding Sq is 0.02molL repeatedly ^-1na ₃pO ₄15.00ml.

2.4.6 the interference of coexisting substances

According to table 1,2, can know much in ultraviolet region, have the inorganic oxygen-containing acid group of absorption all to have interference, but according to document ^[11], in desulfurized gesso of flue gas only a small amount of existence, experiment adopts and adds the dense HCl of 0.5ml to remove, and through three times, washs centrifuging to examining without Cl ^-till.Because BaSO ₄with Ba ₃(PO ₄) ₂k _spgreatly different in size, according to fractional precipitation, precipitation transforming principle, the mode of twice precipitation of this experiment employing, centrifuging, first will with BaSO ₄form separate, be then converted into again Ba ₃(PO ₄) ₂discharge in last supernatant, negative ion is only surplus with excessive two components.

2.4.7 in two Component Systems solving of concentration

In experiment during secondary precipitate after adding, with form two Component Systems, Simultaneous Equations is:

$\left\{\begin{array}{cc}{A}_{193}^{{\mathrm{SO}}_4^{2-}+{\mathrm{PO}}_4^{3-}}=728.8\×C_{{\mathrm{SO}}_4^{2-}}+2707\×C_{{\mathrm{PO}}_4^{3-}}& \left(1\right)\\ A_{210}^{{\mathrm{SO}}_4^{2-}+{\mathrm{PO}}_4^{3-}}=82.50\×C_{{\mathrm{SO}}_4^{2-}}+112.5\×C_{{\mathrm{PO}}_4^{3-}}& \left(2\right)\end{array}\right.$

concentration can try to achieve rapidly by computing machine Excel program.

3. sample determination

Heat-engine plant desulfurized gypsum sample picks up from Huaneng Group power plant, sample adopt back after in 105 ℃ of oven dry, in exsiccator, preserve, then according to the operation of aforementioned mensuration scheme.Experiment key is to make fully precipitation, then fully dissolves again.Series standard solution 0.002,0.004,0.006,0.008,0.010molL ^-1, under wavelength 193.0nm, linear equation is A=32.76C+0.02263, correlation coefficient r=0.9995.With sample blank, by experimental technique, carry out 11 parallel experiments, measurement standard deviation is 0.018%.

Adopt the direct photometry of ultraviolet of drafting herein and compare experiment with muffle furnace gravimetric method, data are as follows:

Anhydrous slufuric acid determination of calcium content result in table 3. desulfurated plaster sample

Comprehensively think: colourless inorganic oxygen-containing acid group has uv absorption, negative ion absorbs stronger, aspect trace, ultramicro-analysis, is being widely used. deng to a little less than ultraviolet absorption, but absorption curve, linear equation are all good, are applied to the macro-analysis of sulfate ion, can replace barium sulphate gravimetric method.

Claims (3)

1. a method that adopts ultraviolet spectrophotometry directly to measure constant sulfate radical, it is characterized in that: for the sample desulfurated plaster that has certain interfering material: accurately take desulfurated plaster 0.0800～0.0900g in beaker, add the dense HCl of 0.50ml, to be no less than the pure distilled water of 50ml, at 40 ℃, under 10min magnetic stirrer, dissolve, add 3.00 * 10-2molL-1 BaCl225.00ml, after stirring the standing BaSO4 of making and fully precipitating, all be transferred in centrifuge tube, centrifugal 15min on 2500r/min hydro-extractor, separated three times of cyclic washing, to examining nothing left Cl-1, supernatant all discards, in BaSO4 precipitation, add 2.0 * 10-2molL-1Na again ₃pO ₄15.00ml, stirs and evenly mixs standingly, makes all, after stripping, together with water lotion, all proceed to centrifuge tube, after centrifuging, get all supernatant dilutions and be settled to 1000ml, at ultraviolet band 193nm and 210nm place, measure respectively absorbance A, by the mode of separating binary linearity Simultaneous Equations, by computing machine Excel program solution, obtain concentration.

2. employing ultraviolet spectrophotometry according to claim 1 is directly measured the method for constant sulfate radical, it is characterized in that: described binary linearity Simultaneous Equations is when precipitating for the second time, after adding, with form two Component Systems, Simultaneous Equations is:

$\left\{\begin{array}{cc}{A}_{193}^{{\mathrm{SO}}_4^{2-}+{\mathrm{PO}}_4^{3-}}=728.8\×C_{{\mathrm{SO}}_4^{2-}}+2707\×C_{{\mathrm{PO}}_4^{3-}}& \left(1\right)\\ A_{210}^{{\mathrm{SO}}_4^{2-}+{\mathrm{PO}}_4^{3-}}=82.50\×C_{{\mathrm{SO}}_4^{2-}}+112.5\×C_{{\mathrm{PO}}_4^{3-}}& \left(2\right)\end{array}\right.$

concentration can try to achieve by computing machine Excel program; Wherein:

be respectively the absorbance recording at ultraviolet band 193nm and 210nm place; for concentration; for concentration.

3. employing ultraviolet spectrophotometry according to claim 1 is directly measured the method for constant sulfate radical, it is characterized in that: separated three times of cyclic washing, and to examining nothing left Cl-1.