CN100494995C - Automatic Analysis Method of Cr6+ in Leather - Google Patents

Abstract

The method comprises: crushing the detected leather into pieces to dry and extract by K2HPO4 solution; filtering to obtain the Cr6+ extract; then, with K2Cr2O4 solution as guide sample, former Cr6+ solution as sample, drawing the spectrum chart of sample, diphenylcarbazide -acetone-H2SO4 solution as color-developing liquid, and acetone-H2SO4 solution as reference liquid, drawing the spectrums for guide sample and sample with analysis device; then, calculating testing result. This invention is simple and high sensitivity up to 0.5 mug/L.

Description

Automatic Analysis Method of Cr6+ in Leather

technical field

The invention belongs to an analysis and detection method of Cr ⁶⁺ in leather, in particular to an automatic analysis and detection method of Cr ⁶⁺ in leather.

Background technique

Hexavalent chromium in leather products is in contact with human skin for a long time, which will cause toxicity to human skin, nervous system and endocrine system. Therefore, countries all over the world, especially developed countries, are paying more and more attention to the content of hexavalent chromium in leather. Testing the content of hexavalent chromium in leather is an important problem or an indispensable link in the production of leather and leather products. As for the analysis and detection of hexavalent chromium in leather, artificial colorimetry is generally used, which is adopted in my country's import and export inspection industry standard SN07404-1997. In this standard, the tested leather is extracted with dipotassium hydrogen phosphate solution with a concentration of 0.02mol/L to obtain the Cr ⁶⁺ extract of the tested leather, which is developed with diphenylcarbazide and detected by spectrophotometry. Because each step adopts manual operation, there are following disadvantages: 1, because the color development of diphenylcarbazide and ^Cr has a certain time limit, the color development time is too long or too short and will affect the measurement result, and manual operation is very difficult. It is difficult to control the consistency of the color development time. Moreover, it is difficult to ensure the accurate quantification of the samples by manual operation, so the analysis sensitivity is low, and the detection limit is only 4 μg/L. 2. Use 0 sample as a reference, so when the sample has high chromaticity and the sample itself has adsorption, the absorption of the sample cannot be corrected, resulting in high measurement results. When the chromaticity is very deep, the high value is larger. 3. The operation is complicated, the analysis time is long (30-40 minutes for analyzing a sample), and the consumption of chemical reagents is large. In addition, the low concentration of dipotassium hydrogen phosphate solution used to extract the tested leather is also a factor affecting the determination results.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide an automatic analysis method for Cr ⁶⁺ in leather, so as to improve the analysis sensitivity and analysis speed and reduce the analysis cost.

The object of the present invention is achieved like this: improve at the deficiencies in the prior art, when preparing the Cr ⁶⁺ extraction solution of tested leather, the concentration of dipotassium hydrogen phosphate solution is increased to 0.06～0.1mol/L, obtains After measuring the Cr ⁶⁺ extract of the leather, the Cr ⁶⁺ was analyzed and detected by the instrument using the reference flow injection analysis method. The instrument used is an automatic analyzer for metal elements, and its patent number is ZL03234986.6

The automatic analysis method of ^Cr in the leather of the present invention, step is as follows successively:

1. Prepare the Cr ⁶⁺ extract of the tested leather

Preparation of the Cr ⁶⁺ extract of tested leather comprises the following procedures:

(1) Dispose of the tested leather into pieces and dry them,

(2) Put the dried leather fragments into the extraction container, then add dipotassium hydrogen phosphate solution with a concentration of 0.06-0.1mol/L, the amount added is 40-60ml/g based on the weight of the leather fragments in the extraction container,

(3) Close the extraction container, extract at room temperature for 2 to 4 hours under shaking,

(4) the extract is filtered to obtain the Cr ^extract of the leather to be tested;

2. Detection and analysis of Cr ⁶⁺

The detection and analysis of Cr ⁶⁺ adopts the reference type flow injection analysis method, and its steps are testing and drawing the spectrogram of the standard sample, testing and drawing the spectrogram of the sample and calculating the test result of the sample;

(1) Test and draw the spectrum of the standard sample

Potassium dichromate aqueous solution is used as the standard sample, diphenylcarbazide-acetone-sulfuric acid aqueous solution is used as the chromogenic solution, and acetone-sulfuric acid aqueous solution is used as the reference solution, and the analytical instrument is operated so that the reference solution and the standard sample enter the liquid flow path And mixed in the liquid flow path, the mixed liquid passes through the optical flow cell to generate a baseline to be measured and drawn, so that the standard sample, chromogenic liquid, and reference liquid enter the liquid flow path, and the reference liquid is pushed into the liquid flow path by the "plug" type The chromogenic solution is mixed with the standard sample entering the liquid flow path and reacts to form a purple compound, and the solution containing the purple compound passes through the optical flow cell to generate a spectrum and is mapped;

(2) Test and draw the spectrum of the sample

The Cr6 ⁺ extract of the tested leather prepared in step 1 is used as a sample, diphenylcarbazide-acetone-sulfuric acid aqueous solution is a color developing solution, and acetone-sulfuric acid aqueous solution is a reference solution, and the analytical instrument is operated so that the reference The liquid and the sample enter the liquid flow path and mix in the liquid flow path. The mixed liquid passes through the optical flow cell to generate a baseline and is mapped. The analysis instrument is operated to make the sample, chromogenic liquid, and reference liquid enter the liquid flow path. The "plug" type chromogenic solution pushed by the specific liquid into the liquid flow path mixes with the sample entering the liquid flow path and reacts to form a purple compound, and the solution containing the purple compound passes through the optical flow cell to generate a spectrum and is mapped;

(3) Calculation of test results

The analytical instrument compares the drawn sample spectrum with the standard sample spectrum, and calculates the content of the measured Cr ⁶⁺ in the sample;

When testing and drawing the spectrum of the standard sample and the test and drawing of the sample, the solutions for testing and drawing the baseline and testing and drawing the spectrum of the analyte should contain equal amounts of the same standard sample or sample.

When preparing the Cr ⁶⁺ extract of the tested leather, in order to isolate the oxygen in the air and prevent the Cr ³⁺ from being oxidized to make the Cr ⁶⁺ measurement result too high, the extraction process can be carried out under the protection of nitrogen, but it can also be carried out without nitrogen protection. , Take measures to strengthen the sealing of the extraction container.

For the dyed finished leather, when preparing the Cr ⁶⁺ extract of the tested leather, colored substances such as dyes will also enter the extract. Although the reference flow injection analysis method can automatically offset the interference caused by chroma, if it is If the concentration of colored substances in the tested leather Cr ⁶⁺ extract is too high, it will also affect the measurement results. Therefore, the tested leather Cr ⁶⁺ extract with too high concentration of colored substances can be decolorized, that is, the obtained by filtering the extract. The leather Cr ⁶⁺ extract was decolorized through the adsorption column. The adsorbent in the adsorption column is macroporous adsorption resin or activated carbon.

Tests show that: in the chromogenic solution used in the above method, the content of diphenylcarbazide is 0.2-0.3 g/L, the content of acetone is 40-60 ml/L, and the content of sulfuric acid is 0.3-0.4 mol/L. In the reference liquid used in the above method, the content of acetone is 40-60ml/L, and the content of sulfuric acid is 0.3-0.4mol/L.

The present invention has the following beneficial effects:

1. Since the Cr ⁶⁺ in the tested leather Cr ⁶⁺ extract is analyzed and detected by the instrument using the reference flow injection analysis method, the analysis sensitivity and analysis speed are improved, and the detection limit can reach 0.5 μg/L. The analysis time of each sample was no more than 10 minutes (3 parallel determinations).

2. By using the reference flow injection analysis method described in the present invention, the color development time can be precisely controlled by controlling the sampling flow rate and the length of the flow path, and the automatic sampling through the sampling loop can ensure the same injection volume each time. , thus good reproducibility and high precision can be obtained.

3. The reference type flow injection analysis method of the present invention can automatically deduct the chromaticity interference in the tested leather Cr ⁶⁺ extract, if the concentration of colored substances in the tested leather Cr ⁶⁺ extract is too high, it will pass through the adsorption column Chromatic interference can be completely eliminated by decolorization.

4. Reagent saving, compared with the method described in my country's import and export inspection industry standard SN 07404-1997, it can save more than 90% of reagents.

5. The operation is simple, the requirements for operators are not high, and it is easy to promote and use.

6. The analytical instruments used are simple in structure, low in price, and easy to use and maintain.

Description of drawings

Fig. 1 is the analysis flow chart of the automatic analysis method of ^Cr in the leather of the present invention and the liquid flow diagram of analytical instrument used;

Figure 2 is a structural diagram of the adsorption column, the adsorption column is in a non-use state;

Fig. 3 is a schematic diagram of the adsorption column in Fig. 2 being in use;

Figure 4 is the chromatograms of two samples analyzed for Cr ⁶⁺ in leather.

In the figure, 1—first low pressure pump, 2—second low pressure pump, 3—injection valve, 4—mixer, 5—color reaction circle, 6—optical flow cell, 7—optical detector, 8—computer , R ₁ —color developing solution, R ₂ —reference solution, S—standard sample or sample, 9—plug, 10—column, 11—adsorbent, 12—filter, 13—sample container.

Detailed ways

Example 1

In this example, the Cr ⁶⁺ in the blue skin provided by a certain chemical factory is tested and analyzed.

The analytical instrument in this embodiment adopts the metal element automatic analyzer disclosed in Patent No. ZL03234986.6 utility model patent (commercially available commodity), its liquid flow path is as shown in Figure 1, and the optical path of the optical flow cell is 10mm , the detection wavelength is 540nm, the pump flow rate is 0.2-1.0ml/min, and the working pressure is 2-3×10 ⁵ Pa.

The operation steps of the test analysis of this embodiment:

1. Prepare standard samples and solutions required for test analysis

(1) Preparation of standard samples

A, take by weighing potassium dichromate (analytical pure) 0.2829g, dry at 105 ℃ for 2 hours, then add high-purity water to dissolve, set the volume to 100ml, and prepare a solution with a concentration of 1.00g/L Cr ⁶⁺ ;

B. Draw 0.1ml of the solution configured in step A and dilute to 100ml to obtain a solution of 1.00mg/L Cr ⁶⁺ ;

C. Take the solutions in step B according to the volumes in the table below, dilute them to 100ml respectively, and prepare a series of standard solutions.

Volume (ml) 0.5 1 2 4 6 8 10 Concentration (μg/L) 5 10 20 40 60 80 100

(2) Preparation of chromogenic solution

A, take by weighing 0.2400g diphenylcarbazide and be dissolved in 50ml acetone;

B. Slowly add 22.2ml of concentrated sulfuric acid into a container containing 500ml of deionized water, stir and cool to room temperature;

C. Mix the diphenylcarbazide acetone solution prepared in step A and the sulfuric acid solution prepared in step B, set the volume to 1000ml, and then transfer it to a brown bottle for dark preservation.

(3) Preparation of reference solution

Take 22.2ml of concentrated sulfuric acid and slowly add it into a container containing 500ml of deionized water, stir and cool to room temperature, then add 50ml of acetone, and set the volume to 1000ml.

2. Prepare the Cr ⁶⁺ extract of the tested leather

(1) Cut the leather to be tested into pieces of 2×2mm, dry them at 100°C for 2 hours, put them in a desiccator and cool them for later use;

(2) Weigh 2.0 ± 0.01 g of dried leather fragments and put them into the extraction container, then add dipotassium hydrogen phosphate solution with a concentration of 0.1 mol/L to the extraction container, and the addition amount is 100 ml;

(3) Evacuate the air, seal the extraction container, and extract at room temperature on a shaker for 3 hours;

(4) Filter the extract to obtain the Cr ⁶⁺ extract of the tested leather.

3. Test drawing spectrogram

(1) Test and draw the spectrum of the standard sample

Operate the analytical instrument so that the reference solution _R2 and the standard sample S are sent to the mixer 4 by the second low-pressure pump 2 for mixing, and then sent to the color reaction circle 5 for further thorough mixing and then enter the optical flow cell 6, then they can be displayed on the computer 8 Obtain a stable baseline; under the action of the first low-pressure pump 1, the chromogenic liquid R ₁ is sent to the injection valve 3, and under the action of the second low-pressure pump 2, the reference liquid R ₂ is sent to the injection valve 3 The standard sample S is sent to the mixer 4, and the reference solution pushes the "plug"-type chromogenic solution to mix with the standard sample in the mixer 4, and the mixed solution enters the color reaction circle 5 for further mixing and reaction to form a purple-red compound , the solution containing the purple-red compound enters the optical flow cell 6, and the spectrum of the standard sample can be obtained on the computer 8.

(2) Test and draw the spectrum of the sample

Operate the analytical instrument so that the reference solution _R2 and the sample S are sent to the mixer 4 by the second low-pressure pump 2 for mixing, sent to the color reaction circle 5 for further thorough mixing, and then enter the optical flow cell 6, and then they can be displayed on the computer 8 Obtain a stable baseline; under the action of the first low-pressure pump 1, the chromogenic liquid R ₁ is sent to the injection valve 3, and under the action of the second low-pressure pump 2, the reference liquid R ₂ is sent to the injection valve 3 , The sample S is sent to the mixer 4, and the reference solution pushes the "plug"-type chromogenic solution to mix with the sample in the mixer 4, and the mixed solution enters the color reaction circle 5 for further mixing and reacts to form a purple-red compound , the solution containing the purple compound enters the optical flow cell 6, and the spectrum of the sample can be obtained on the computer 8. The sample spectrograms obtained in this embodiment are the first group of spectrograms in FIG. 4 .

4. Calculation of test results

The computer compares the spectrogram of the sample with the spectrogram of the standard sample, and calculates that the Cr ⁶⁺ content of the tested leather in the sample is 0.62mg/kg.

Note: When injecting samples, the solutions for drawing the baseline and testing for the spectrum of the analyte should contain equal amounts of the same standard sample or sample.

Example 2

In this example, the Cr ⁶⁺ in black cowhide provided by a tannery was tested and analyzed.

The analytical instrument in this embodiment adopts the metal element automatic analyzer disclosed in Patent No. ZL03234986.6 utility model patent (commercially available commodity), its liquid flow path is as shown in Figure 1, and the optical path of the optical flow cell is 10mm , the detection wavelength is 540nm, the pump flow rate is 0.2-1.0ml/min, and the working pressure is 2-3×10 ⁵ Pa.

The operation steps of the test analysis of this embodiment:

1. Prepare standard samples and solutions required for test analysis

(1) Preparation of standard samples

Preparation standard sample is identical with embodiment 1.

(2) Preparation of chromogenic solution

A, take by weighing 0.2800g diphenylcarbazide and dissolve in 60ml acetone;

B. Slowly add 23.0ml of concentrated sulfuric acid into a container containing 500ml of deionized water, stir and cool to room temperature;

C. Mix the diphenylcarbazide acetone solution prepared in step A and the sulfuric acid solution prepared in step B, and set the volume to 1000ml, then transfer to a brown bottle and store in the dark.

(3) Preparation of reference solution

Take 23.0ml of concentrated sulfuric acid and slowly add it into a container containing 500ml of deionized water, stir and cool to room temperature, then add 60ml of acetone, and set the volume to 1000ml.

2. Prepare the Cr ⁶⁺ extract of the tested leather

(1) Cut the leather to be tested into pieces of 2×2mm, dry them at 100°C for 2 hours, put them in a desiccator and cool them for later use;

(2) Weigh 2.0 ± 0.01 g of dried leather fragments and put them into an extraction container, then add a dipotassium hydrogen phosphate solution with a concentration of 0.8 mol/L to the extraction container, and the addition amount is 110 ml;

(3) Evacuate the air, seal the extraction container and feed nitrogen into the extraction container, and extract at room temperature on a shaker for 3.5 hours;

(4) filtering the extract;

(5) decolorize the filtrate through the adsorption column. The structure of the adsorption column is as shown in Figure 2 and Figure 3. It is composed of a column body 10, a plug 9, an adsorbent 11 and a filter element 12 positioned in the column body, and the adsorbent is selected from styrene -divinylbenzene high molecular polymer (commercially available), particle size 50～80 mesh, concrete operation is as follows:

A. Fix the adsorption column on the stand, and pull out the plug 9,

B. Add a small amount of water to wet the adsorbent in the adsorption column, then slowly add the filtrate obtained in step (4) into the adsorption column,

C. After discarding the initial 2-3ml decolorizing solution, the decolorizing solution collected in the sample container is the Cr ⁶⁺ extract of the leather to be tested.

3. Test drawing spectrogram

The operation is the same as in Example 1, and the drawn sample spectrograms are the second group of spectrograms in FIG. 4 .

4. Calculation of test results

The computer compares the spectrogram of the sample with the spectrogram of the standard sample, and calculates that the Cr ⁶⁺ content of the tested leather in the sample is 1.20mg/kg.

Claims (8)

1, a kind of automatic analysis method of ^Cr in leather, it is characterized in that step is as follows successively: (1) Prepare the Cr ⁶⁺ extract of tested leather Preparation of the Cr ⁶⁺ extract of tested leather comprises the following procedures: A. Dispose of the tested leather into pieces and dry them, B. Put the dried leather fragments into the extraction container, then add dipotassium hydrogen phosphate solution with a concentration of 0.06-0.1mol/L, the amount added is 40-60ml/g based on the weight of the leather fragments in the extraction container, C. Seal the extraction container and extract at room temperature for 2 to 4 hours under shaking. D, the extract is filtered to obtain the Cr ⁶⁺ extract of the tested leather; (2) Detection and analysis of Cr ⁶⁺ The detection and analysis of Cr ⁶⁺ adopts the reference type flow injection analysis method, and its steps are to test and draw the spectrum of the standard sample, test and draw the spectrum of the sample and calculate the test results; A. Test and draw the spectrum of the standard sample Potassium dichromate aqueous solution is used as the standard sample, diphenylcarbazide-acetone-sulfuric acid aqueous solution is used as the chromogenic solution, and acetone-sulfuric acid aqueous solution is used as the reference solution, and the analytical instrument is operated so that the reference solution and the standard sample enter the liquid flow path And mixed in the liquid flow path, the mixed liquid passes through the optical flow cell to generate a baseline to be measured and drawn, so that the standard sample, chromogenic liquid, and reference liquid enter the liquid flow path, and the reference liquid is pushed into the liquid flow path by the "plug" type The chromogenic solution is mixed with the standard sample entering the liquid flow path and reacts to form a purple compound, and the solution containing the purple compound passes through the optical flow cell to generate a spectrum and is mapped; B. Test and draw the spectrum of the sample With the ^Cr of the tested leather prepared in step (1) extracting solution as sample, diphenylcarbazide-acetone-sulfuric acid aqueous solution as color developing solution, acetone-sulfuric acid aqueous solution as reference solution, operating analysis instrument, make The reference liquid and the sample enter the liquid flow path and mix in the liquid flow path. The mixed liquid passes through the optical flow cell to generate a baseline and is mapped, so that the sample, chromogenic liquid, and reference liquid enter the liquid flow path, and the reference liquid The "plug" type chromogenic solution pushed into the liquid flow path is mixed with the sample entering the liquid flow path and reacts to form a purple compound, and the solution containing the purple compound passes through the optical flow cell to generate a spectrum and is mapped; C. Calculation of test results The analytical instrument compares the drawn sample spectrum with the standard sample spectrum, and calculates the content of the measured Cr ⁶⁺ in the sample; When testing and drawing the spectrum of the standard sample and the test and drawing of the sample, the solutions for testing and drawing the baseline and testing and drawing the spectrum of the analyte should contain equal amounts of the same standard sample or sample. 2. The automatic analysis method for Cr ⁶⁺ in leather according to claim 1, characterized in that the extraction process for preparing the Cr ⁶⁺ extract of the leather to be tested is carried out under nitrogen protection. 3. The automatic analysis method for Cr ⁶⁺ in leather according to claim 1 or 2, characterized in that the preparation of the Cr ⁶⁺ extract of the leather to be tested also includes a decolorization process, that is, the Cr 6+ of the tested leather obtained by filtering the extract ^{The 6+} extract is decolorized through the adsorption column. 4. The automatic analysis method for Cr ⁶⁺ in leather according to claim 3, characterized in that the adsorbent in the adsorption column is macroporous adsorption resin or activated carbon. 5. The automatic analysis method for Cr ⁶⁺ in leather according to claim 1 or 2, characterized in that in the chromogenic solution, the content of diphenylcarbazide is 0.2-0.3 g/L, and the content of acetone is 40 ～60ml/L, the content of sulfuric acid is 0.3～0.4mol/L. 6. The automatic analysis method for Cr ⁶⁺ in leather according to claim 3, characterized in that in the chromogenic solution, the content of diphenylcarbazide is 0.2-0.3g/L, and the content of acetone is 40-60ml /L, the content of sulfuric acid is 0.3-0.4mol/L. 7. The automatic analysis method for Cr ⁶⁺ in leather according to claim 1 or 2, characterized in that in the reference solution, the content of acetone is 40-60ml/L, and the content of sulfuric acid is 0.3-0.4mol/L. 8. The automatic analysis method for Cr ⁶⁺ in leather according to claim 3, characterized in that in the reference solution, the content of acetone is 40-60ml/L, and the content of sulfuric acid is 0.3-0.4mol/L.

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