Test paper for formaldehyde detection and preparation method thereof

Abstract

The invention discloses test paper for formaldehyde detection and a preparation method thereof, and belongs to the field of chemical detection. The method comprises the following steps: immersing chromatographic paper into a soak solution prepared from a sodium hydroxide solution, a phloroglucinol solution and an antioxidant in proportion to obtain formaldehyde detection test paper, and adjusting the proportional relation of the three to ensure that the obtained test paper is clear in color development and long in quality guarantee period, so that accurate formaldehyde concentration detection can be realized; in addition, the formaldehyde detection test paper provided by the invention is simple to prepare, relatively low in cost and relatively high in sensitivity.

Description

Technical Field

[0001] The invention relates to a test paper for formaldehyde detection and a preparation method thereof, and belongs to the field of formaldehyde chemical detection. Background Art

[0002] Formaldehyde test paper detects formaldehyde content through chemical reactions. The test paper is coated with specific chemical reagents. When it comes into contact with formaldehyde in the air, the reagent will change color, and the depth of the color is directly proportional to the concentration of formaldehyde. Finally, the formaldehyde concentration range is judged by a colorimetric card.

[0003] A Chinese patent with publication number CN104280389A discloses a method for detecting formaldehyde in beverages. The method utilizes the condensation reaction of formaldehyde with phloroglucinol under alkaline conditions of sodium hydroxide to generate an orange-red compound, and the formaldehyde content is finally determined by colorimetric quantification. However, the orange-red compound generated by formaldehyde and phloroglucinol under alkaline conditions fades quickly and has unstable color development, which may affect the colorimetric operation and thus affect the accuracy of the test results.

[0004] A Chinese patent with publication number CN114635308A discloses a high color difference formaldehyde detection test paper based on natural pigments, which produces a specific color change by utilizing the reaction of natural pigments with formaldehyde; however, natural pigments are sensitive to the external environment and may cause the test paper to fade or change color during storage, and the test paper can only perform qualitative detection of formaldehyde, and it is difficult to achieve accurate quantitative detection of formaldehyde concentration.

[0005] The Chinese patent with publication number CN104359902A discloses a formaldehyde colorimetric test paper and its preparation method and application. The test paper is formed by reacting formaldehyde with acetylacetone in A color reaction occurs under excessive conditions, and the depth of color is proportional to the formaldehyde concentration; however, the test paper has a low detection sensitivity and may be interfered by other aldehyde substances (such as acetaldehyde and propionaldehyde), thus affecting the accuracy of the test results. Summary of the invention

[0006] In order to solve the problems of unstable color development and easy oxidation of reagents in the prior art, the present invention provides a test paper for formaldehyde detection and its preparation and detection method, by soaking chromatographic paper with sodium hydroxide solution and phloroglucinol solution of different ratios and concentrations for 10 minutes and drying, dripping the solution to be tested to form a concentration gradient, and testing a group of reagent ratios with the clearest color development and the longest shelf life of the test paper, thereby enhancing the stability and clarity of color development. At the same time, the present invention adds an antioxidant sodium ascorbate or tea polyphenols to the reagent, controls the oxidation of the phloroglucinol reagent, greatly prolongs the shelf life of the test paper, and improves the accuracy of formaldehyde detection.

[0007] The first object of the present invention is to provide a method for preparing a formaldehyde detection test paper, the method comprising:

[0008] Step 1: mixing a sodium hydroxide solution, a phloroglucinol solution and an antioxidant solution to obtain a soaking solution; in the soaking solution, the concentration ratio (M, mol / L) of the sodium hydroxide, the phloroglucinol and the antioxidant is 0.15-0.2: 0.001-0.002: 0.05-0.08;

[0009] Step 2: Soak the chromatography paper in the soaking solution and dry it to obtain the formaldehyde detection test paper.

[0010] In one embodiment, the antioxidant solution in step 1 includes sodium ascorbate or tea polyphenols.

[0011] In one embodiment, the soaking method in step 2 is to soak 8 to 10 cm 2 Soak in 8-10 mL of soaking solution for 10-12 minutes;

[0012] Optionally, place 9 cm 2 Soak in 10 mL of soaking solution for 10 min.

[0013] In one embodiment, the drying in step 2 is cold air drying.

[0014] In one embodiment, the drying in step 2 is cold air drying, which is performed at a distance of 10 cm from the test paper for 5 minutes.

[0015] In one embodiment, when preparing the soaking solution, the antioxidant is added first to ensure that the reagent is protected earlier;

[0016] In one embodiment, when preparing the soaking solution, the phloroglucinol solution should be slowly added after the sodium hydroxide solution to prevent precipitation or oxidation caused by excessive local temperature.

[0017] The second object of the present invention is to provide a formaldehyde detection test paper prepared by any of the above methods.

[0018] The third object of the present invention is to provide a formaldehyde detection product, comprising the formaldehyde detection test paper as claimed in claim 1.

[0019] The fourth object of the present invention is to provide a method for detecting formaldehyde, using the formaldehyde detection test paper as claimed in claim 1, the detection method is:

[0020] Soak the sample to be tested in deionized water to obtain a soaked solution, drop the soaked solution on the formaldehyde detection test paper, let it stand, and detect the gray value of the test paper;

[0021] Substitute the gray value into the standard curve to calculate the formaldehyde concentration;

[0022] The standard curve is:

[0023] 0.2043x-209.91+y=0, R 2 =0.9909, (0≤x≤200)

[0024] Among them, y represents the gray value, x represents the formaldehyde concentration, mg / kg, R 2 Represents goodness of fit.

[0025] In one embodiment, the sample to be tested is immersed in deionized water for more than 25 minutes.

[0026] In one embodiment, the amount of solution added after immersion is 25 μL / cm 2 ; The standing time is 2 minutes.

[0027] A fifth object of the present invention is to provide the use of any of the above methods or the above formaldehyde detection test paper or the above formaldehyde detection product or the above formaldehyde detection method in detecting formaldehyde in food or sewage.

[0028] The beneficial effects of the present invention are:

[0029] The invention provides a test paper for formaldehyde detection and a preparation method thereof. The method achieves clearer and more stable color development of the formaldehyde detection test paper and improves the accuracy of the detection result by adjusting the concentrations of a sodium hydroxide solution and a phloroglucinol solution and the ratio between the two. The test paper can be stored for a long time by adding sodium ascorbate or tea polyphenols in a precise ratio to sodium hydroxide and phloroglucinol. The formaldehyde detection test paper provided by the invention is easy to prepare, has a low cost, and has a high sensitivity.

[0030] Specifically,

[0031] When the sample tested was squid, the recovery rate reached 95.14%;

[0032] When the sample tested was beef tripe, the recovery rate reached 92.05%;

[0033] When the test sample was sewage, the recovery rate reached 96.83%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of the test results of the test paper for formaldehyde detection prepared in Example 1;

[0035] Figure 2 This is a standard curve diagram of formaldehyde concentration-grayscale value of the test paper for formaldehyde detection prepared in Example 1. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0037] Source of raw materials:

[0038] Chromatographic paper was purchased from the official website of Sinopharm Reagents;

[0039] Phloroglucinol was purchased from the official website of Aladdin Reagent, CAS number: 6099-90-7;

[0040] Tea polyphenols were purchased from the official website of Aladdin Reagent;

[0041] Sodium ascorbate was purchased from the official website of Aladdin Reagent;

[0042] Example 1

[0043] The method for preparing formaldehyde detection test paper using sodium ascorbate as an antioxidant comprises the following steps:

[0044] (1) mixing a 0.8 M sodium hydroxide solution, a 0.01 M phloroglucinol solution, and a 0.4 M sodium ascorbate solution in a volume ratio of 3:1:1 to obtain a soaking solution;

[0045] (2) 9cm 2 The chromatography paper (1 cm × 9 cm) was placed in 10 mL of soaking solution and soaked for 10 min; after being fully soaked, it was taken out and dried with cold air for 5 min to quickly remove the solvent; the dried chromatography paper was cut into test paper pieces of 1 × 1 cm to obtain formaldehyde detection test paper.

[0046] Comparative Example 1

[0047] On the basis of Example 1, the sodium ascorbate solution was replaced with anthocyanin, and the remaining steps were the same as in Example 1 to prepare a formaldehyde detection test paper. Anthocyanin has good antioxidant properties, but it is a natural pigment and is blue-purple when the reagent is alkaline, which interferes with the color judgment of the subsequent reaction between formaldehyde and the reagent, and cannot be used for test paper preservation.

[0048] Comparative Example 2

[0049] On the basis of Example 1, the sodium ascorbate solution was replaced with ascorbic acid (vitamin C), and the remaining steps were consistent with Example 1 to prepare a formaldehyde test paper. Vitamin C has good antioxidant properties, but is acidic, with a pH value between 3.2 and 5.5, and is easy to react with sodium hydroxide in the mixed solution, destroying the solution ratio of sodium hydroxide and phloroglucinol, while reducing antioxidant substances and weakening antioxidant properties, which is not suitable for test paper preservation.

[0050] Comparative Example 3

[0051] On the basis of Example 1, the concentration of sodium ascorbate solution was changed to 0.8 M, and the remaining steps were consistent with Example 1 to prepare formaldehyde detection test paper. Too high a concentration of sodium ascorbate affects the content of sodium hydroxide and phloroglucinol in the mixed solution, interferes with the color judgment of the later reaction of formaldehyde and reagents, and a high concentration of antioxidants cannot be used for test paper preservation.

[0052] Comparative Example 4

[0053] On the basis of Example 1, the concentration of sodium ascorbate solution was changed to 0.2 M, and the remaining steps were consistent with Example 1 to prepare formaldehyde detection test paper. The concentration of sodium ascorbate was too low, the antioxidant effect was poor, and the shelf life was short. Low concentration antioxidants cannot be used for test paper shelf life.

[0054] Example 2

[0055] 1. Construct a formaldehyde concentration-gray value standard curve

[0056] Aqueous solutions with formaldehyde concentrations of 10 mg / kg, 20 mg / kg, 40 mg / kg, 60 mg / kg, 80 mg / kg, 100 mg / kg and 200 mg / kg were prepared respectively, and 25 μL was dropped on the formaldehyde detection test paper prepared in Example 1 and allowed to stand for 2 min.

[0057] After standing, the formaldehyde test paper will react with color. Figure 1 As shown, the grayscale analysis is performed on the color of the entire test paper surface to obtain the grayscale value. Different formaldehyde concentrations are fitted with their corresponding grayscale values ​​to construct a formaldehyde concentration-grayscale value standard curve.

[0058] The specific process of grayscale calculation is as follows:

[0059] S1: Image acquisition: Use Android Studioa programming software to write an app function so that it can connect to the mobile phone camera, use the camera to shoot the target color test paper, convert the light signal into an electrical signal, and finally obtain a digital image. The image is usually in color and represented by the pixel values ​​of the three color channels of red (R), green (G), and blue (B).

[0060] S2: Color conversion: convert the collected color image from RGB color space to grayscale color space. The common conversion formula is: grayscale value = 0.299×R+0.587×G+0.114×B. The weight is determined according to the sensitivity of the human eye to different colors. The RGB value of each pixel is calculated through this formula to obtain the corresponding grayscale value.

[0061] S3: Grayscale quantization: Discretize the calculated continuous range of grayscale values ​​according to a certain quantization level. For example, for a common 8-bit grayscale image, the grayscale value range is quantized into 256 levels from 0 to 255, where 0 represents pure black and 255 represents pure white.

[0062] S4: Grayscale value acquisition and application; after quantization, each pixel has a certain grayscale value.

[0063] The standard curve is as follows Figure 2 As shown, the details are as follows:

[0064] 0.2043x-209.91+y=0, R 2 =0.9909, (0≤x≤200)

[0065] Where y represents the gray value, x represents the formaldehyde concentration, mg / kg; R 2 Represents goodness of fit.

[0066] 2. Use formaldehyde test strips and standard curves to detect formaldehyde content in food

[0067] (1) Detection of formaldehyde content in squid

[0068] Squid purchased from the market was taken, washed, membrane removed, cut into squid meat samples, and repeatedly pressed with filter paper to dry, and the samples were respectively immersed in deionized water (25 minutes) to obtain immersed solutions.

[0069] Take 20μg of the soaked solution and add it to the dried test paper. No color is shown. The squid purchased on the market does not contain formaldehyde. Therefore, the recovery rate is tested by adding external standards to evaluate the accuracy of the test.

[0070] (2) Detection of formaldehyde content in beef tripe

[0071] Take beef tripe (25 minutes) purchased on the market, wash and remove the membrane, cut into beef tripe samples, press repeatedly with filter paper to dry, and soak the samples in deionized water to obtain soaked squid samples.

[0072] Take 20μg of the soaked solution and add it to the dried test paper. No color is shown. The beef tripe purchased on the market does not contain formaldehyde. Therefore, the recovery rate is tested by adding external standards to evaluate the accuracy of the test.

[0073] (3) Experimental recovery rate verification

[0074] Recovery rate refers to the process of adding a known concentration of a standard substance to the sample to be tested during a detection experiment, and evaluating the accuracy of the test by comparing the ratio of the measured concentration change before and after the addition to the added concentration.

[0075] (The recovery rate is calculated as follows: Recovery rate % = (spike value - unspike value) / expected value × 100%.)

[0076] Select rocket squid and beef tripe purchased on the market, wash them repeatedly and remove the membrane. Cut into white squid meat and beef tripe samples, press and dry them repeatedly with filter paper, so that the net weight of each sample after removing water is 0.2g. Soak each sample for 25 minutes with 1.5ml of formaldehyde solution with concentrations of 10mg / kg, 20mg / kg, 40mg / kg, 60mg / kg, 80mg / kg, 100mg / kg, 150mg / kg and 200mg / kg. Add 20μg of beef tripe extract (or the extract after squid is soaked for 25 minutes) and initial concentration formaldehyde solution to the surface of the test paper prepared in Example 1, 3 times for each group (to reduce errors, select the average value), and let it stand for 2 minutes. Measure the gray value of each test paper and convert it to the displayed formaldehyde concentration using the standard curve in 1. Calculate the recovery rate.

[0077] The test results of the average formaldehyde concentration (mg / kg) in squid, beef tripe and pure formaldehyde and the test results of the recovery rate are shown in Table 1, Table 2, Table 3 and Table 4:

[0078] Table 1 Test results of average formaldehyde concentration in squid

[0079]

[0080]

[0081] Table 2 Test results of average formaldehyde concentration in beef tripe

[0082]

[0083] Table 3 Average formaldehyde concentration test results in pure formaldehyde solution

[0084]

[0085] Table 4 Test results of recovery rates of squid, beef tripe and pure formaldehyde solution

[0086]

[0087]

[0088] The results show that the formaldehyde test paper prepared in Example 1 and its standard curve can accurately detect the formaldehyde content in food (squid, beef tripe), and the recovery rates are above 93% and 90%, respectively.

[0089] 4. Detect formaldehyde content in sewage

[0090] The national standard "Comprehensive Wastewater Discharge Standard" (GB8978-1996) stipulates that the formaldehyde content of the secondary discharge standard shall not be higher than 2 mg / kg. 1 mg / kg, 1.5 mg / kg, and 2.5 mg / kg formaldehyde aqueous solutions were prepared to simulate sewage.

[0091] After the sewage was diluted 5 times, 25 μL was dropped on the formaldehyde detection test paper, and the formaldehyde content was calculated according to the gray value. The results are shown in Table 5.

[0092] Table 5 Formaldehyde detection results in sewage

[0093] Initial concentration Test strips for concentration after dilution Test strips for concentration conversion Recovery rate (%) 1mg / kg 0.19mg / kg 0.2mg / kg 96.31％ 1.5 mg / kg 0.29mg / kg 0.3mg / kg 95.43％ 2.5 mg / kg 0.49mg / kg 0.5mg / kg 98.75％

[0094] 5. Test strip stability test

[0095] The formaldehyde test paper prepared in Example 1 was placed at 40°C ± 2°C and a relative humidity of 75% ± 5% for 6 months (according to the Chinese Pharmacopoeia 2015, this accelerated process is equivalent to being placed at 25°C ± 2°C and a relative humidity of 60% ± 5% for 12 months).

[0096] According to the method of squid 2 (taking soaking in 100 mg / kg formaldehyde solution as an example), the accuracy of the test paper for formaldehyde content was tested 6 months later. The results showed that the recovery rate reached 96.32%.

[0097] 6. Take the formaldehyde detection test paper prepared in Comparative Examples 1 to 4 and evaluate its formaldehyde detection accuracy

[0098] (1) The formaldehyde concentration-grayscale standard curves of the formaldehyde detection test papers of Comparative Examples 1 to 4 were fitted according to the method in 1. The results are shown in Table 6.

[0099] Table 6 Standard curve

[0100] example Fitting curve Comparative Example 1 Interference with color development, unable to fit Comparative Example 2 <![CDATA[y=-0.3073x+224.1R 2 =0.9498]]> Comparative Example 3 <![CDATA[y=-0.4109x+231.27R 2 =0.961]]> Comparative Example 4 <![CDATA[y=-0.3127x+224.17R 2 =0.9503]]>

[0101] (2) The formaldehyde test papers prepared in Comparative Examples 1 to 4 were placed at 40°C ± 2°C and a relative humidity of 75% ± 5% for 6 months.

[0102] According to the method of squid 2 (taking soaking in 100 mg / kg formaldehyde solution as an example), the accuracy of the formaldehyde detection test papers prepared in Comparative Examples 1 to 4 was tested, and the results are shown in Table 7.

[0103] Table 7 Test results

[0104] example Recovery rate (%) Comparative Example 1 Unable to measure Comparative Example 2 81.75％ Comparative Example 3 87.12％ Comparative Example 4 85.32％

[0105] Example 3

[0106] On the basis of Example 1, the sodium ascorbate solution was replaced by a tea polyphenol solution, and the remaining steps were the same as in Example 1 to prepare a formaldehyde detection test paper. After testing, the standard curve corresponding to the formaldehyde detection test paper prepared with tea polyphenol as an antioxidant was:

[0107] y+0.2009x-207.91=0, R 2 =0.9723, (0≤x≤200)

[0108] Where y represents the gray value, x represents the formaldehyde concentration, mg / kg; R 2 Represents goodness of fit.

[0109] The detection recovery rate of formaldehyde-containing foods using the formaldehyde detection test paper and the standard curve reaches more than 95.3%.

[0110] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a formaldehyde detection test paper, characterized in that: The method is: Step 1: mixing a sodium hydroxide solution, a phloroglucinol solution and an antioxidant solution to obtain a soaking solution; in the soaking solution, the concentration ratio of the sodium hydroxide, the phloroglucinol and the antioxidant is 0.15-0.2: 0.001-0.002: 0.05-0.08; Step 2: Soak the chromatography paper in the soaking solution and dry it to obtain the formaldehyde detection test paper.

2. The method according to claim 1, characterized in that The antioxidant solution in step 1 includes sodium ascorbate or tea polyphenols.

3. The method according to claim 1, characterized in that The soaking method in step 2 is to soak 8 to 10 cm 2 Soak the chromatographic paper in 8-10 mL of soaking solution for 10-12 minutes; Optionally, place 9 cm 2 Soak the chromatography paper in 10 mL of soaking solution for 10 min.

4. The method according to claim 1, characterized in that The drying in step 2 is cold air drying.

5. Formaldehyde detection test paper prepared by the method according to any one of claims 1 to 4.

6. A formaldehyde detection product, characterized in that: Contains the formaldehyde detection test paper according to claim 5.

7. A method for detecting formaldehyde, characterized in that: Using the formaldehyde detection test paper described in claim 5, the detection method is: Soak the sample to be tested in deionized water to obtain a soaked solution, drop the soaked solution on the formaldehyde detection test paper, let it stand, and detect the gray value of the test paper; Substitute the gray value into the standard curve to calculate the formaldehyde concentration; The expression of the standard curve is: 0.2043x-209.91+y=0 Wherein, x represents the formaldehyde concentration, mg / kg; y represents the gray value, 0<x≤200.

8. The method according to claim 7, characterized in that The samples to be tested were immersed in deionized water for more than 25 min.

9. The method according to claim 7, characterized in that: The amount of solution added after immersion is 25 μL / cm 2 ; The standing time is 2 minutes.

10. Use of the method according to claims 1 to 4 or the formaldehyde detection test paper according to claim 5 or the formaldehyde detection product according to claim 6 or the formaldehyde detection method according to claims 7 to 9 in detecting formaldehyde in food or sewage.

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