Oxygen isotope standard sample of nitrite as well as preparation method and application of oxygen isotope standard sample

Abstract

The invention relates to a preparation method and application of an oxygen isotope standard sample of nitrite. According to the preparation method, nitrite and specific delta < 18 > O water are mixed to obtain a nitrite solution, the nitrite and the water can be subjected to oxygen atom exchange under specific pH and closed conditions of the nitrite solution, and then nitrite oxygen isotope standard samples with different oxygen isotope values are obtained. According to the preparation method, the oxygen isotope standard sample of the nitrite can be simply and conveniently prepared, and the oxygen isotope value range of the obtained oxygen isotope standard sample of the nitrite is large, so that the application of isotope analysis of the nitrite of an unknown sample is expanded; the method can be applied to isotope analysis in the fields of pollution traceability, food safety inspection or biochemical reaction kinetics process research.

Description

Technical Field

[0001] The invention relates to the technical field of experimental analysis methods, and in particular to an oxygen isotope standard sample of nitrite and a preparation method and application thereof. Background Art

[0002] As an intermediate product of nitrogen transformation, nitrite has the potential to accumulate in terrestrial and aquatic ecosystems, but it is often overlooked in river nitrogen monitoring. In order to fully explain the production and consumption of nitrite during the nitrogen cycle in the aquatic environment and explain its accumulation mechanism, it is necessary to perform oxygen isotope analysis on nitrite. When determining and analyzing the oxygen isotope of nitrite, the sample needs to be converted into nitrous oxide gas, and then the oxygen isotope value of nitrite is obtained by analyzing the isotope composition of nitrous oxide under the calibration of the oxygen isotope standard sample of nitrite.

[0003] In order to meet the isotope analysis of unknown samples, standard samples are usually required to have a wide range of isotope values. The oxygen isotope value range of industrially synthesized nitrite is currently small (between -10 and 0‰), which restricts its application as an oxygen isotope standard sample or severely limits the oxygen isotope analysis of nitrite.

[0004] Wang Zheng et al. (see the document Preparation of Oxygen Isotope Standard Samples, Journal of Peking University (Natural Science Edition), Vol. 25, No. 2, 1989) pointed out that to prepare standard samples with different oxygen isotope abundances, two samples with different isotope compositions must be prepared first, one of which can be a natural abundance sample and the other a high abundance sample. The two samples can be mixed in proportion to prepare standard samples with different isotope compositions for guiding isotope analysis. However, for the preparation of nitrite oxygen isotope standard samples, nitrite with high oxygen abundance is difficult to obtain, so it is impossible to prepare nitrite isotope standard samples directly by mixing two isotope samples.

[0005] In summary, the current problem of lack of preparation method for oxygen isotope standard samples of nitrite needs to be solved urgently. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the problem of the current lack of a preparation method for an oxygen isotope standard sample of nitrite, and to provide a preparation method for an oxygen isotope standard sample of nitrite. The preparation method can not only easily prepare oxygen isotope standard samples of nitrite with different oxygen isotope values, but also the oxygen isotope value range of the obtained oxygen isotope standard samples of nitrite is wide.

[0007] Another object of the present invention is to provide an oxygen isotope standard sample of nitrite.

[0008] Another object of the present invention is to provide an application of the above oxygen isotope standard sample of nitrite in isotope analysis.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing a standard sample of oxygen isotopes of nitrite comprises the following steps:

[0011] Adding nitrite to water to obtain a nitrite solution, placing the nitrite solution under airtight conditions at a pH of 2 to 4 for ≥20 days, and drying to obtain an oxygen isotope standard sample of the nitrite;

[0012] The δ of the water 18 O is -55~+100‰.

[0013] The inventors of the present invention have found that the combination of nitrite and a specific δ 18 O and water to obtain a nitrite solution. Under a specific pH and closed conditions (anaerobic), nitrite and water can exchange oxygen atoms to obtain oxygen isotope standard samples of nitrite with different oxygen isotope values. This preparation method can not only easily prepare oxygen isotope standard samples of nitrite, but also the obtained oxygen isotope standard samples of nitrite have a wide range of oxygen isotope values, which expands the application of isotope analysis of nitrite in unknown samples.

[0014] If the pH is too low, a large amount of acid needs to be added during the preparation process, and the acid in the obtained product is difficult to completely remove during the drying step, and the prepared oxygen isotope standard sample of nitrite is not pure enough to be used as a standard sample. At the same time, adding a large amount of acid will cause safety hazards. If the pH is too high (such as pH ≥ 5), it is difficult for nitrite to exchange oxygen atoms with water, and it is difficult to obtain an oxygen isotope standard sample of nitrite.

[0015] If left in an open environment, nitrite may be oxidized by oxygen, making it impossible to obtain a standard sample of nitrite oxygen isotope.

[0016] If the standing time is too short, the degree of oxygen atom exchange between nitrite and water is low, so that a specific oxygen isotope standard sample of nitrite cannot be obtained.

[0017] Preferably, the water has a δ 18 O is regulated by: 18 O of water mix.

[0018] In the present invention, the δ 18O can specifically be -55‰, -50‰, -40‰, -30‰, -20‰, -10‰, +5‰, +10‰, +20‰, +30‰, +40‰, +50‰, +60‰, +70‰, +80‰, +90‰, and +100‰.

[0019] In the present invention, the δ 18 O can be obtained by different δ 18 For example, the δ 18 O can be calculated according to the following formula:

[0020] δ 18 O=f 1 ×δ 18 O 1 +f 2 ×δ 18 O 2 In the formula, δ 18 O 1 is the oxygen isotope value of water depleted in oxygen isotope; δ 18 O 2 is the oxygen isotope value of heavy oxygen water;

[0021] f 1 is the ratio of the mass of oxygen isotope-depleted water to the total mass of oxygen isotope-depleted water and heavy oxygen water, f 2 It is the ratio of the mass of heavy oxygen water to the total mass of water depleted in oxygen isotope and heavy oxygen water.

[0022] More preferably, the different 18 The water of O is at least one of deionized water, glacial water or heavy oxygen water.

[0023] Further preferably, the heavy oxygen water 18 The isotope abundance of O is 10~99atom%.

[0024] In the present invention, the δ of the heavy oxygen water is 18 O can be calculated according to the following formula:

[0025] (1)R sample =A 18O / A 16O

[0026] In the formula, A 18O for 18 O isotope abundance; A 16O for 16 O isotope abundance, A 16O =1-A 18O ; R sample for18 O and 16 isotopic abundance ratio of O (dimensionless);

[0027] (2)

[0028] In the formula, R sample for 18 O and 16 Isotope abundance ratio of O (dimensionless); R standard Vienna standard mean seawater 18 O and 16 The isotopic abundance ratio of O is 2.0052×10 -3 .

[0029] Preferably, the placement time is 20 to 35 days.

[0030] Preferably, the δ of the nitrite 18 O is -10~0‰.

[0031] Preferably, the nitrite is at least one of sodium nitrite or potassium nitrite.

[0032] More preferably, the nitrite is sodium nitrite.

[0033] Preferably, the placement temperature is 20-30°C.

[0034] Preferably, the pH is adjusted by hydrochloric acid.

[0035] Preferably, the concentration of the nitrite solution is 1-5 mol / L.

[0036] Preferably, the step of grinding is further included after the drying.

[0037] A standard sample of oxygen isotopes of nitrite, wherein the δ 18 O is -55~-10.01‰ or +0.01~+100‰.

[0038] The application of the above oxygen isotope standard sample of nitrite in isotope analysis is also within the protection scope of the present invention.

[0039] Preferably, the isotope analysis is oxygen isotope analysis of nitrite.

[0040] Preferably, the isotope analysis is isotope analysis for pollution source tracing, isotope analysis in the field of food safety inspection, or isotope analysis for studying the kinetic process of biochemical reactions.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] The present invention combines nitrite and specific delta 18 O is mixed with water to obtain a nitrite solution. Under a specific pH and closed conditions, nitrite and water can exchange oxygen atoms to obtain oxygen isotope standard samples of nitrite with different oxygen isotope values. The preparation method can not only easily prepare oxygen isotope standard samples of nitrite, but also the oxygen isotope value range of the obtained oxygen isotope standard samples of nitrite is wide, which expands the application of isotope analysis of nitrite of unknown samples, such as isotope analysis in pollution tracing, isotope analysis in the field of food safety inspection, or isotope analysis in the study of kinetic processes of biochemical reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the δ of the oxygen isotope standard samples of nitrite in Examples 1 to 3 18 O value.

[0044] Figure 2 The oxygen isotope standard samples of nitrite in Examples 1 to 3 are prepared by 18 The graph of the change of O value with the placement time.

[0045] Figure 3 The oxygen isotope standard samples of nitrite in Examples 1 to 3 are converted into N by the azide method. 2 Delta of O 18 O value and the δ 18 O value plotted as a standard curve.

[0046] Figure 4 To determine the δ 18 O value. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. In the present invention, the technical features described in an open manner include a closed technical solution composed of the listed features, and also include an open technical solution containing the listed features. In the present invention, it is related to a numerical interval (i.e., a numerical range). If not otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. If not otherwise specified, when the numerical interval only points to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical range disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numeric interval" allows broadly including percentage interval, proportion interval, ratio interval and other numerical interval types.

[0048] Example 1

[0049] This embodiment provides a method for preparing an oxygen isotope standard sample of nitrite, the preparation method comprising the following steps:

[0050] Sodium nitrite (Macklin) was added to δ 18 O is -9.72‰ water (deionized water, homemade) to obtain a 4.3 mol / L sodium nitrite solution, and the pH of the sodium nitrite solution is adjusted to 4 with 1 mol / L HCl solution, and then the sodium nitrite solution is sealed and stored in a glass bottle with a tetrachloroethylene plastic cap for 35 days, freeze-dried and ground into powder to obtain the oxygen isotope standard sample of nitrite.

[0051] Example 2

[0052] This embodiment provides a method for preparing a standard sample of oxygen isotopes of nitrite, which is different from that of embodiment 1 in that: 18 O is -9.72‰ water replaced by δ 18 O is -20.52‰ water (5100 glacier water, commercially available).

[0053] Example 3

[0054] This embodiment provides a method for preparing a standard sample of oxygen isotopes of nitrite, which is different from that of embodiment 1 in that: 18O is -9.72‰ water replaced by δ 18 O is +73.12‰ water. 18 Water with an O content of +73.12‰ is 18 Heavy oxygen water with an O isotope abundance of 10atom% (commercially available, δ 18 O theoretical value is +54411.49‰) and deionized (δ 18 O is -9.72‰) and water in a volume ratio of 1:499.

[0055] Example 4

[0056] This embodiment provides a method for preparing an oxygen isotope standard sample of nitrite, which is different from Embodiment 1 in that the pH of the sodium nitrite solution is adjusted to 2.

[0057] Example 5

[0058] This embodiment provides a method for preparing an oxygen isotope standard sample of nitrite, which is different from Embodiment 1 in that sodium nitrite is replaced by potassium nitrite.

[0059] Performance Testing

[0060] (1) Oxygen isotope value of standard sample of nitrite (δ 18 O) Determination

[0061] Determination method: The elemental analysis-stable isotope ratio mass spectrometer (EA-IRMS) system is used for determination. The oxygen atoms in the product of the high-temperature cracking of the standard sample of nitrite react with the particulate carbon to produce CO, which is then analyzed by the isotope ratio mass spectrometer. The specific process is: weigh a sample containing 0.6 μmol into a 3.5×5 mm silver foil capsule, load it into the automatic sampler of the elemental analyzer, and crack it at 1325°C. The gas produced in the reactor is separated by gas chromatography using helium as the carrier gas to separate N 2 and CO, and the CO peaks were monitored at m / z 28 and 30 to determine the δ 18 O. It was calibrated using nitrate nitrogen standards USGS34, USGS35, and IAEA. The results are as follows: Figure 1 The results are shown in Table 1. The samples tested included untreated sodium nitrite (Macklin) and the oxygen isotope standard samples of nitrites of Examples 1 to 3. The results are shown in Table 1.

[0062] Table 1

[0063]

[0064] As can be seen from Table 1, different δ 18O value of nitrite oxygen isotope standard sample. Among them, the δ 18 O(δ 18 O is -9.72‰) lower than the delta of sodium nitrite 18 O(δ 18 O is -9.98±0.57‰), but the δ 18 O is smaller than sodium nitrite, which may be caused by a certain degree of equilibrium fractionation effect in the exchange of oxygen atoms between water and sodium nitrite. The preparation methods of Examples 4 and 5 can also prepare oxygen isotope standard samples of nitrite, and the oxygen isotope value (δ 18 O) The results are similar to those in Example 1.

[0065] (2) In the process of preparing the oxygen isotope standard samples of nitrite in Examples 1 to 3, the solutions were freeze-dried and ground into powder after 14 days and 35 days respectively, and their δ 18 O value, and then plot the δ 18 The change law of O value with placement time is shown in the figure below. Figure 2 As shown. Figure 2 It can be seen that with the increase of storage time, the oxygen isotope value of the oxygen isotope standard sample of nitrite gradually approaches the oxygen isotope value of the water used in preparation, and basically reaches stability after 20 days, indicating that by adjusting the oxygen isotope value of the water used in preparation, after being placed under certain conditions for a period of time, an oxygen isotope standard sample of nitrite with a certain oxygen isotope value can be obtained.

[0066] (3) Application

[0067] The oxygen isotope value of nitrite in a river in a certain city was determined by the azide method. The determination method is as follows:

[0068] Mix 20% acetic acid and 2M potassium azide in a volume ratio of 1:1 to obtain potassium azide acetate buffer. Flush the potassium azide acetate buffer with 40 mL / min of helium for 20 minutes to remove N 2 O. The potassium azide acetate buffer was prepared and used on the day of use.

[0069] Weigh the oxygen isotope standard samples of nitrite from Examples 1 to 3 and prepare 0.3 mgN / L NaNO 2 2 mL of nitrite oxygen isotope standard sample was prepared into NaNO 2The solution and the water sample to be tested (water samples collected from five rivers in a certain city) were placed in a 12mL headspace injection bottle, and the vial was covered with a polytetrafluoroethylene-lined septum. 2mL of potassium azide-acetic acid buffer was added to each vial through a syringe, and the vial was shaken vigorously at 220r / min for 15 minutes to convert nitrite into nitrous oxide. After 15 minutes, 1mL of 6M sodium hydroxide was added with a syringe and shaken to make the solution alkaline to terminate the reaction. The hydroazide (HN) produced by the reaction 3 ) is volatile and toxic, so the reaction process must be carried out in a fume hood.

[0070] The oxygen isotope value of nitrous oxide converted from nitrite in the solution is determined by an online gas preparation and introduction device coupled with a stable isotope ratio mass spectrometer (GB-IRMS), wherein the oxygen isotope value of the oxygen isotope standard sample of nitrite is used to draw a standard curve, such as Figure 3 As shown, the oxygen isotope value of nitrous oxide obtained by converting nitrite in the water sample to be tested is substituted into the standard curve for correction to obtain the oxygen isotope value of nitrite in the water sample to be tested, such as Figure 4 shown.

[0071] Figure 4 The point names in are named as follows: river name + point + sampling depth (cm). Among them, "TX", "CB", "SH", "SC", and "HP" are the first, second, third, fourth, and fifth rivers, respectively. For example: TX1-0 and TX1-20 are the point names of the first river site 1 with sampling depths of 0 cm and 20 cm, respectively; TX2-0 and TX2-20 are the point names of the first river site 2 with sampling depths of 0 cm and 20 cm, respectively; CB1-0 and CB1-20 are the point names of the second river site 1 with sampling depths of 0 cm and 20 cm, respectively.

[0072] from Figure 3 It can be seen that the prepared oxygen isotope standard sample of nitrite was converted into N 2 In the standard curve drawn after O, δ 18 O N2O Value and δ 18 O NO2 - The values ​​are linearly positively correlated, R 2 The value is 0.9995, indicating that the oxygen isotope standard sample of nitrite prepared by the present invention can realize the determination and calibration of the oxygen isotope of nitrite in water samples.

[0073] from Figure 4 It can be seen that the water samples collected from five rivers in a city were measured by the azide method to obtain δ 18 O NO2-The values ​​range from -12.27‰ to -3.99‰, with an average value of -10.02‰.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a standard sample of oxygen isotopes of nitrite, characterized in that: The following steps are involved: Adding nitrite to water to obtain a nitrite solution, placing the nitrite solution under airtight conditions at a pH of 2 to 4 for ≥20 days, and drying to obtain an oxygen isotope standard sample of the nitrite; The δ of the water 18 O is -55~+100‰.

2. The preparation method according to claim 1, characterized in that: The δ of water 18 O is regulated by: 18 O of water mix.

3. The preparation method according to claim 1, characterized in that: The placement time is 20 to 35 days.

4. The preparation method according to claim 1, characterized in that: The nitrite is at least one of sodium nitrite or potassium nitrite.

5. The preparation method according to claim 1, characterized in that: The placement temperature is 20-30°C.

6. The preparation method according to claim 1, characterized in that: The pH was adjusted with hydrochloric acid.

7. The preparation method according to claim 1, characterized in that: The concentration of the nitrite solution is 1-5 mol / L.

8. A standard sample of oxygen isotopes of nitrite, characterized in that: The δ of nitrite 18 O is -55~-10.01‰ or +0.01~+100‰.

9. Use of the oxygen isotope standard sample of nitrite according to claim 8 in isotope analysis.

10. The use according to claim 9, characterized in that: The isotope analysis is isotope analysis for pollution source tracing, isotope analysis in the field of food safety inspection, or isotope analysis for studying the kinetic process of biochemical reactions.

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