A method for measuring aluminum content using chrome azurol S spectrophotometry

Abstract

The invention discloses a method for measuring aluminum content by chrome azuro blue S spectrophotometry, comprising: digesting a sample, removing acid, and fixing the volume to obtain a digestion solution; removing the digestion solution, adding an appropriate amount of sodium hydroxide solution, standing for a period of time, and centrifuging to obtain a first supernatant and a first precipitate; taking the first precipitate, adding an appropriate amount of sodium hydroxide solution, and vortexing, transferring the vortexed solution to a microwave digestion tank, performing microwave treatment, and after the microwave treatment, centrifuging the solution again to obtain a second supernatant and a second precipitate; combining the first supernatant and the second supernatant, adding an appropriate amount of nitric acid, and performing heating and concentration treatment to obtain a solution to be tested. The invention can accurately measure the aluminum content by using the chrome azuro blue S spectrophotometry when a large amount of iron is contained in food.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum content determination, in particular to a method for measuring aluminum content by using a chrome azurol S spectrophotometric method. Background Art

[0002] When using the chrome azuro blue S spectrophotometry to detect the aluminum content in food, since chrome azuro blue S can form colored complexes with a variety of metal ions, the selectivity of the color developer of this method is not high. Common metal ions such as iron, manganese, copper, and zinc will interfere with it, especially iron. However, since the instrument used in the chrome azuro blue S spectrophotometry is inexpensive, simple to operate, and has high sensitivity, this method is still widely used.

[0003] At present, there are many reports on eliminating the interference of other metal ions on the aluminum content measured by chrome azuro blue S. The most widely used method is the masking method. Commonly used masking agents include ascorbic acid solution, zinc ethylenediaminetetraacetic acid solution, thioglycolic acid, etc. The addition of masking agents can indeed accurately measure the aluminum content within a certain range, but the masking ability of masking agents is limited. If there are a large number of interfering ions in the sample, the effect of the masking agent will be greatly reduced, and the use conditions of the masking agent are harsh. For example, the pH value of zinc ethylenediaminetetraacetic acid solution is 4-6. In addition, the metal industry uses sodium hydroxide to roast aluminum to generate water-soluble aluminate, thereby separating it from other metals. This method has a high roasting temperature, and the measured aluminum is lost. It is only suitable for the detection of aluminum in metals and not for the detection of aluminum in food. There are also reports in the metal industry that after the sample is dissolved in acid, sodium hydroxide is added to separate aluminum from other metals, and then the aluminum is detected. However, this detection method is not the chrome azuro blue S spectrophotometry method. The chrome azuro blue S spectrophotometry method detects aluminum, and the aluminum must be AL 3+ The state can be measured, and aluminum will co-precipitate with other alkali metals (magnesium hydroxide, calcium hydroxide, zinc hydroxide, etc.), causing aluminum to no longer dissolve in strong alkali, resulting in aluminum being unable to be detected. This method does not solve this problem. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a method for measuring aluminum content by chrome azuro blue S spectrophotometry. By adopting this method, when the food contains a large amount of iron, the aluminum content can be accurately measured by chrome azuro blue S spectrophotometry.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for measuring aluminum content by chrome azurol S spectrophotometry, comprising the following steps:

[0006] Step 1, the sample is digested, acid is removed, and volume is fixed to obtain a digestion solution;

[0007] Step 2, remove the solution, add an appropriate amount of sodium hydroxide solution, let it stand for a period of time and then centrifuge to obtain the first supernatant and the first precipitate;

[0008] Step 3, adding an appropriate amount of sodium hydroxide solution to the first precipitate and vortexing, transferring the vortexed solution to a microwave digestion tank for microwave treatment, and after the microwave treatment, centrifuging the solution again to obtain a second supernatant and a second precipitate;

[0009] Step 4, combining the first supernatant and the second supernatant, adding an appropriate amount of nitric acid and heating and concentrating the mixture to obtain a solution to be tested;

[0010] Step 5: Measure the aluminum content in the solution to be tested by chrome azuro blue S spectrophotometry.

[0011] Preferably, the step 1 is specifically as follows:

[0012] Weigh 0.3g-0.8g of sample into a microwave digestion tank, add 5mL-10mL nitric acid, use a microwave digestion instrument to control the temperature at 180℃-210℃ for microwave treatment for 30min-40min, after digestion, remove the acid at 140℃-160℃ until the solution is about 0.5mL-1mL, make up to volume with water, and mix well to obtain the digestion solution.

[0013] Preferably, the step 2 is specifically as follows:

[0014] Measure 5mL-10mL of digestion solution into a centrifuge tube, add 1-2 drops of p-nitrophenol solution, adjust the solution to yellow with 1moL / L-2moL / L sodium hydroxide solution, add 0.5mL-1.0mL of 1moL / L-2moL / L sodium hydroxide solution, mix well, let stand for 20min-60min, centrifuge at 4000r / min-8000r / min for 5min-10min, separate the supernatant and the precipitate to obtain the first supernatant and the first precipitate.

[0015] Preferably, the step 3 is specifically as follows:

[0016] Take the first precipitate and add 5mL-10mL of 5mmoL / L-10mmoL / L sodium hydroxide solution, vortex for 5min-10min to make the precipitate form a suspension. After vortexing, transfer it to a microwave digestion tank and use a microwave digestion instrument for microwave treatment. The microwave treatment temperature is 140℃-210℃ and the time is 10min-40min. After treatment, take out the digestion tank, transfer the solution to a centrifuge tube, centrifuge at 4000r / min-8000r / min for 5min-10min, separate the supernatant and the precipitate, and obtain the second supernatant and the second precipitate.

[0017] Preferably, the step 4 is specifically as follows:

[0018] Combine the first supernatant and the second supernatant, add 1mL-2mL of nitric acid, place on a heating plate and heat at 140℃-180℃ until the solution is less than 5mL-10mL, take out the solution, wait for the solution to cool, and then dilute the solution to 5mL-10mL with water to obtain the solution to be tested.

[0019] Preferably, the step 5 is specifically as follows:

[0020] Take 1mL-2mL of the test solution and add 1 drop of p-nitrophenol ethanol solution, mix well, add ammonia solution (1+1) until light yellow, then add nitric acid solution (2.5%) until the yellow just disappears, add 1mL more, add 1mL ascorbic acid solution (10g / L), mix well, add 3mL chrome blue S solution (1g / L), mix well, add 1mL TritonX-100 solution (3%), 3mL CPB solution (3g / L), 3mL ethylenediamine-hydrochloric acid buffer solution in turn, add water to 25.0mL, mix well, and let stand for 40min. At a wavelength of 620nm, use a 1cm colorimetric dish to measure the absorbance value with a blank solution as a reference. Use the mass of aluminum in the standard series solution as the horizontal coordinate and the corresponding absorbance value as the vertical coordinate, and draw a standard curve. Quantify according to the absorbance value of the test solution compared with the standard curve.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention adopts microwave treatment technology for the first time to solve the problem of co-precipitation of aluminum and other alkali metals (magnesium hydroxide, calcium hydroxide, zinc hydroxide, etc.), ensuring that aluminum can be dissolved again in a strong alkaline solution, and then aluminum can be measured;

[0023] 2. The present invention eliminates the interference of some metals on the chrome azuro blue S spectrophotometric measurement of aluminum, especially iron, and solves the problem of high results when the chrome azuro blue S spectrophotometric measurement of aluminum is adopted when the food contains a large amount of iron, thereby ensuring the accuracy of the test results. DETAILED DESCRIPTION

[0024] The embodiments of the present invention are described in detail below.

[0025] Example 1

[0026] A method for measuring aluminum content by chrome azurol S spectrophotometry, comprising:

[0027] The sample is digested, acid is removed and volume is fixed to obtain a digestion solution, the digestion solution is removed, an appropriate amount of sodium hydroxide solution is added, and the solution is centrifuged after standing for a period of time to obtain a first supernatant and a precipitate, an appropriate amount of sodium hydroxide solution is added to the precipitate and vortexed, the vortexed solution is transferred to a microwave digestion tank, and a reasonable microwave treatment is performed. After the microwave treatment, the solution is centrifuged again to obtain a second supernatant and a precipitate, the first supernatant and the second supernatant are combined, an appropriate amount of nitric acid is added, and the solution is heated and concentrated, and finally the chrome azuro blue S spectrophotometric method is used for detection.

[0028] Sample digestion: weigh 0.3 g of sample into a microwave digestion tank, add 5 mL of nitric acid, and use a microwave digestion instrument at 210°C for 30 min. After digestion, remove the acid at 160°C until the solution is about 0.5 mL, dilute to 25 mL with water, and mix well to obtain the digestion solution.

[0029] Treatment of digestion solution: measure 5 mL of digestion solution into a centrifuge tube, add 1 drop of p-nitrophenol solution, adjust the color to yellow with 1 mol / L sodium hydroxide solution, add 0.5 mL of 2 mol / L sodium hydroxide solution, mix well, let stand for 20 minutes, centrifuge at 8000 r / min for 5 minutes, separate the supernatant and the precipitate, and obtain the first supernatant and the first precipitate.

[0030] Take the first precipitate and add 5mL 10moL / L sodium hydroxide solution, vortex for 5min to make the precipitate form a suspension. After vortexing, immediately transfer it to a microwave digestion tank and use a microwave digestion instrument for microwave treatment. The microwave treatment temperature is 210℃ and the time is 10min. After treatment, take out the digestion tank, transfer the solution to a centrifuge tube, centrifuge at 8000r / min for 5min, separate the supernatant and the precipitate, and obtain the second supernatant and the second precipitate.

[0031] Combine the first and second supernatants, add 1 mL of nitric acid, place on a heating plate and heat at 180°C until the solution is less than 5 mL, take out the solution, wait for the solution to cool, and then dilute the solution to 5 mL with water to obtain a treated solution.

[0032] Chrome Azure S spectrophotometric method for measuring aluminum content: Take 2mL of treatment solution or 2mL of digestion solution or 2mL of the first supernatant and add 1 drop of p-nitrophenol solution, mix well, add ammonia solution (1+1) until light yellow, then add nitric acid solution (2.5%) until the yellow just disappears, add 1mL more, add 1mL ascorbic acid solution (10g / L), mix well, add 3mL Chrome Azure S solution (1g / L), mix well, add 1mL TritonX-100 solution (3%), 3mL CPB solution (3g / L), 3mL ethylenediamine-hydrochloric acid buffer solution in turn, add water to 25.0mL, mix well, and let stand for 40min. At a wavelength of 620nm, use a 1cm cuvette to measure the absorbance value with a blank solution as a reference. Use the mass of aluminum in the standard series solution as the horizontal axis and the corresponding absorbance value as the vertical axis, and draw a standard curve. Quantify according to the absorbance value of the test solution compared with the standard curve.

[0033] ICP-MS measurement of aluminum and iron content: the internal standard method is used to measure aluminum and iron in the treatment solution and digestion solution. Scandium is used as the internal standard for aluminum, and germanium is used as the internal standard for iron. The signal response values ​​of aluminum, iron, scandium and germanium are measured. The concentration of the element to be measured is used as the horizontal coordinate, and the ratio of the response signal value of the element to be measured to the selected internal standard element is used as the vertical coordinate. The standard curve is drawn, and the signal response values ​​of iron, aluminum, and scandium and germanium internal standard elements in the digestion solution and the treated digestion solution are determined. The concentrations of iron and aluminum in the digestion solution are obtained according to the standard curve.

[0034] Example 2

[0035] A method for measuring aluminum content by chrome azurol S spectrophotometry, comprising:

[0036] The sample is digested, acid is removed and volume is fixed to obtain a digestion solution, the digestion solution is removed, an appropriate amount of sodium hydroxide solution is added, and the solution is centrifuged after standing for a period of time to obtain a first supernatant and a precipitate, an appropriate amount of sodium hydroxide solution is added to the precipitate and vortexed, the vortexed solution is transferred to a microwave digestion tank, and a reasonable microwave treatment is performed. After the microwave treatment, the solution is centrifuged again to obtain a second supernatant and a precipitate, the first supernatant and the second supernatant are combined, an appropriate amount of nitric acid is added, and the solution is heated and concentrated, and finally the chrome azuro blue S spectrophotometric method is used for detection.

[0037] Sample digestion: weigh 0.8 g of sample into a microwave digestion tank, add 10 mL of nitric acid, and use a microwave digestion instrument to microwave at 180°C for 40 min. After digestion, remove the acid at 140°C until the solution is 1.0 mL, dilute to 50 mL with water, and mix well to obtain the digestion solution.

[0038] Treatment of digestion solution: measure 10mL of digestion solution into a centrifuge tube, add 2 drops of p-nitrophenol solution, adjust the color to yellow with 2moL / L sodium hydroxide solution, add 1.0mL of 1moL / L sodium hydroxide solution, mix well, let stand for 60min, centrifuge at 4000r / min for 10min, separate the supernatant and the precipitate, and obtain the first supernatant and the first precipitate.

[0039] Take the first precipitate and add 10mL 5moL / L sodium hydroxide, vortex for 10 minutes to make the precipitate form a suspension. After vortexing, immediately transfer it to a microwave digestion tank and use a microwave digestion instrument for microwave treatment. The microwave treatment temperature is 140°C and the time is 40 minutes. After treatment, take out the digestion tank, transfer the solution to a centrifuge tube, centrifuge at 4000r / min for 10 minutes, separate the supernatant and the precipitate, and obtain the second supernatant and the second precipitate.

[0040] Combine the first and second supernatants, add 2 mL of nitric acid, place on a heating plate and heat at 140° C. until the solution is less than 10 mL, take out the solution, wait for the solution to cool, and then dilute the solution to 10 mL with water to obtain a treated solution.

[0041] Determination of aluminum content by chrome azuro blue S spectrophotometry: Take 1 mL of the treated solution or 1 mL of the digested solution or 1 mL of the first supernatant, and the rest is the same as in Example 1.

[0042] ICP-MS measurement of aluminum and iron contents: consistent with Example 1.

[0043] All the above test results are converted into sample content mg / kg using the measured concentration value and the sample weight.

[0044] According to the above-mentioned Example 1 and Example 2, 6 batches of bean products containing a large amount of iron were measured respectively. The specific test results are shown in Table 1 and Table 2:

[0045] Table 1 Results of chrome azurol S spectrophotometric measurement of aluminum (mg / kg)

[0046]

[0047] Table 2 ICP-MS measurement results of aluminum and iron (mg / kg)

[0048]

[0049] As shown in Table 1 and Table 2, all six batches of samples contain a large amount of iron. The results of aluminum content measured by ICP-MS and chrome azuro blue S spectrophotometry in the digestion solution are very different. The results measured by chrome azuro blue S spectrophotometry are 25%-450% higher than those measured by ICP-MS. When the chrome azuro blue S spectrophotometry measures the first supernatant, the aluminum content in some samples is significantly reduced, and it can even be considered that it is not detected, indicating that some samples do have substances that can cause aluminum to co-precipitate, causing aluminum hydroxide to no longer dissolve in strong alkaline solutions. The iron measured in the treatment solution is significantly lower than the iron measured in the digestion solution, indicating that the iron in the solution is removed after treatment by this method. The treatment solution is measured by ICP-MS and chrome azuro blue S spectrophotometry, and the results of the two are consistent. Therefore, this method overcomes the interference of iron on aluminum and the problem of aluminum co-precipitation with other substances, and ensures the accuracy of chrome azuro blue S spectrophotometry in measuring aluminum in high-iron samples.

[0050] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for measuring aluminum content in food by chrome azurol S spectrophotometry, characterized in that: The following steps are involved: Step 1, the sample is digested, acid is removed, and volume is fixed to obtain a digestion solution; The step 1 is specifically as follows: Weigh 0.3g-0.8g of sample into a microwave digestion tank, add 5mL-10mL nitric acid, use a microwave digestion instrument to control the temperature at 180℃-210℃ for 30min-40min, after digestion, remove the acid at 140℃-160℃ until the solution is 0.5mL-1mL, dilute with water, mix well to obtain the digestion solution; Step 2, remove the solution, add an appropriate amount of sodium hydroxide solution, let it stand for a period of time and then centrifuge to obtain the first supernatant and the first precipitate; Step 3, adding an appropriate amount of sodium hydroxide solution to the first precipitate and vortexing, transferring the vortexed solution to a microwave digestion tank for microwave treatment, and after the microwave treatment, centrifuging the solution again to obtain a second supernatant and a second precipitate; The step 3 is as follows: Take the first precipitate and add 5mL-10mL of 5mmoL / L-10mmoL / L sodium hydroxide solution, vortex for 5min-10min to make the precipitate form a suspension. After vortexing, transfer it to a microwave digestion tank and perform microwave treatment with a microwave digestion instrument. The microwave treatment temperature is 140℃-210℃ and the time is 10min-40min. After the treatment, take out the digestion tank, transfer the solution to a centrifuge tube, centrifuge at 4000r / min-8000r / min for 5min-10min, separate the supernatant and the precipitate, and obtain a second supernatant and a second precipitate; Step 4, combining the first supernatant and the second supernatant, adding an appropriate amount of nitric acid and heating and concentrating the mixture to obtain a solution to be tested; The step 4 is specifically as follows: Combine the first supernatant and the second supernatant, add 1 mL-2 mL of nitric acid, place on a heating plate at 140°C-180°C and heat until the solution is less than 5 mL-10 mL, take out the solution, wait for the solution to cool, and dilute the solution to 5 mL-10 mL with water to obtain the solution to be tested; Step 5: Measure the aluminum content in the solution to be tested by chrome azuro blue S spectrophotometry.

2. The method for measuring aluminum content in food by chrome azurol S spectrophotometry according to claim 1, characterized in that: The step 2 is specifically as follows: Measure 5mL-10mL of digestion solution into a centrifuge tube, add 1-2 drops of p-nitrophenol solution, adjust the solution to yellow with 1moL / L-2moL / L sodium hydroxide solution, add 0.5mL-1.0mL of 1moL / L-2moL / L sodium hydroxide solution, mix well, let stand for 20min-60min, centrifuge at 4000r / min-8000r / min for 5min-10min, separate the supernatant and the precipitate to obtain the first supernatant and the first precipitate.

3. The method for measuring aluminum content in food by chrome azurol S spectrophotometry according to claim 1, characterized in that: The step 5 is specifically as follows: Take 1mL-2mL of the solution to be tested and add 1 drop of p-nitrophenol solution, mix well, add ammonia solution until it turns light yellow, then add nitric acid solution until the yellow just disappears, add 1mL of nitric acid solution, mix well, add 3mL of chrome azuro blue S solution, mix well, add 1mL of TritonX-100 solution, 3mL of CPB solution, 3mL of ethylenediamine-hydrochloric acid buffer solution in sequence, add water to make up to 25.0mL, mix well, and let stand for 40min; at a wavelength of 620nm, use a 1cm colorimetric dish to measure the absorbance value with a blank solution as a reference, with the mass of aluminum in the standard series solution as the horizontal coordinate and the corresponding absorbance value as the vertical coordinate, and draw a standard curve, and compare the absorbance value of the solution to be tested with the standard curve for quantification.

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