CN117169319A - Oxygen isotope measurement method - Google Patents
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 61
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 61
- 239000001301 oxygen Substances 0.000 title claims abstract description 61
- 238000000691 measurement method Methods 0.000 title claims description 3
- 235000013399 edible fruits Nutrition 0.000 claims abstract description 41
- 235000013311 vegetables Nutrition 0.000 claims abstract description 39
- 238000000034 method Methods 0.000 claims abstract description 38
- 238000001514 detection method Methods 0.000 claims abstract description 29
- GGCZERPQGJTIQP-UHFFFAOYSA-N sodium;9,10-dioxoanthracene-2-sulfonic acid Chemical compound [Na+].C1=CC=C2C(=O)C3=CC(S(=O)(=O)O)=CC=C3C(=O)C2=C1 GGCZERPQGJTIQP-UHFFFAOYSA-N 0.000 claims abstract description 27
- 238000001819 mass spectrum Methods 0.000 claims abstract description 26
- ZCYVEMRRCGMTRW-UHFFFAOYSA-N 7553-56-2 Chemical compound [I] ZCYVEMRRCGMTRW-UHFFFAOYSA-N 0.000 claims abstract description 19
- 229910052740 iodine Inorganic materials 0.000 claims abstract description 19
- 239000011630 iodine Substances 0.000 claims abstract description 19
- 239000008346 aqueous phase Substances 0.000 claims abstract description 18
- 238000004949 mass spectrometry Methods 0.000 claims abstract description 17
- 238000007323 disproportionation reaction Methods 0.000 claims abstract description 13
- 238000004896 high resolution mass spectrometry Methods 0.000 claims abstract description 10
- 239000007788 liquid Substances 0.000 claims abstract description 10
- 238000004364 calculation method Methods 0.000 claims abstract description 6
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- 239000000243 solution Substances 0.000 claims description 38
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims description 33
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 21
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims description 10
- 235000007688 Lycopersicon esculentum Nutrition 0.000 claims description 10
- 241000220225 Malus Species 0.000 claims description 10
- 240000003768 Solanum lycopersicum Species 0.000 claims description 10
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 claims description 10
- 150000002500 ions Chemical class 0.000 claims description 7
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 claims description 6
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 claims description 6
- 238000002347 injection Methods 0.000 claims description 6
- 239000007924 injection Substances 0.000 claims description 6
- 239000007864 aqueous solution Substances 0.000 claims description 5
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 claims description 4
- 239000003960 organic solvent Substances 0.000 claims description 4
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- 239000012895 dilution Substances 0.000 claims description 3
- CQLFBEKRDQMJLZ-UHFFFAOYSA-M silver acetate Chemical compound [Ag+].CC([O-])=O CQLFBEKRDQMJLZ-UHFFFAOYSA-M 0.000 claims description 3
- 229940071536 silver acetate Drugs 0.000 claims description 3
- 241000167854 Bourreria succulenta Species 0.000 claims description 2
- 240000008067 Cucumis sativus Species 0.000 claims description 2
- FOIXSVOLVBLSDH-UHFFFAOYSA-N Silver ion Chemical compound [Ag+] FOIXSVOLVBLSDH-UHFFFAOYSA-N 0.000 claims description 2
- 235000019693 cherries Nutrition 0.000 claims description 2
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- 235000011301 Brassica oleracea var capitata Nutrition 0.000 claims 1
- 235000001169 Brassica oleracea var oleracea Nutrition 0.000 claims 1
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- 235000015103 Malus silvestris Nutrition 0.000 claims 1
- 229910002651 NO3 Inorganic materials 0.000 claims 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims 1
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Abstract
The application relates to the technical field of element detection and analysis, in particular to an oxygen isotope determination method, which comprises the following steps: crushing a vegetable and fruit sample, and then performing heating treatment to obtain distilled liquid distilled from the vegetable and fruit sample; adding silver salt and an organic solution containing elemental iodine into the distillate to perform disproportionation reaction, and then collecting an aqueous phase solution; for IO in aqueous phase solution 3 ‑ Performing high-resolution mass spectrometry detection to obtain oxygen isotope mass spectrometry information; IO from oxygen isotope mass spectrometry information 3 ‑ A basal peak, 17 O mass spectrum signal 18 Performing isotope ratio calculation on the O mass spectrum signal to obtain delta of moisture in the vegetable and fruit sample 17 O value and delta 18 O value. The application can realize the effect of separating vegetable and fruit water 17 O and 18 o is detected rapidly and accurately at the same time, and the method has good application prospect.
Description
Technical Field
The application belongs to the technical field of element detection and analysis, and particularly relates to an oxygen isotope determination method.
Background
The isotope analysis technology has wide application prospect in the food safety field. The water molecules composed of different oxygen isotopes have different vapor pressures due to the difference of mass numbers, and the oxygen isotopes are fractionated by transpiration, so that plant cell moisture is richer in oxygen heavy isotopes than surface water/underground water, therefore, the oxygen isotope proportion has typical latitude effect, land effect and climate and season effect, contains rich production area information, becomes a key traceability factor for production area identification, and is an important index for representing the production area characteristics of agricultural products. The method has very important significance in rapidly and accurately measuring the oxygen stable isotope ratio in the agricultural products.
Moisture is one of main components of vegetables and fruits, such as vegetables and fruits, so that the moisture is an ideal target substance for tracing the agricultural products. According to literature reports, the current determination of the oxygen stable isotope ratio of moisture is mainly based on Isotope Ratio Mass Spectrometry (IRMS) detection, for example, by converting oxygen (O) isotopes into oxygen-containing gas by a physical or chemical method and sending the oxygen-containing gas to an IRMS mass spectrometer for determination, and two technical routes exist at present: firstly, collecting moisture contained in a sample, reacting an oxygen-containing substance with carbon by adopting a high-temperature cracking method to obtain CO gas, and measuring by using IRMS; secondly, off-line balancing or on-line balancing is adopted to make the water vapor and the exogenous gas (such as CO) 2 ) After the equilibrium exchange, the measurement was performed by IRMS. The former is easy to be interfered by other oxygen-containing components in the water, the accuracy of the result is affected, and the latter has the following defects although the application is more: (1) The isotope balancing process takes a long time (typically tens of hours); (2) Carbonyl in sampleThe base organic matters (ketone, aldehyde and acid) and alcohols are easy to carry out isotope exchange with the balance reaction gas, and interfere with the measurement result; (3) IRMS has difficulty distinguishing CO 2 In (a) 13 C, C and C 17 The O isotope peak (molecular weight is 45) and therefore can only be measured 18 O is difficult to measure simultaneously 17 O and 18 O。
disclosure of Invention
The application aims to provide an oxygen isotope determination method, which aims to solve the problem of how to rapidly and accurately detect delta of moisture in vegetable and fruit samples 17 O value and delta 18 O value.
In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:
the embodiment of the application provides an oxygen isotope determination method, which comprises the following steps:
crushing a vegetable and fruit sample, and then performing heating treatment to obtain distilled liquid distilled from the vegetable and fruit sample;
adding silver salt and an organic solution containing elemental iodine into the distillate to perform disproportionation reaction, and then collecting an aqueous phase solution;
for IO in the aqueous phase solution 3 - Performing high-resolution mass spectrometry detection to obtain oxygen isotope mass spectrometry information;
IO from the oxygen isotope mass spectrometry information 3 - A basal peak, 17 O mass spectrum signal 18 Performing isotope ratio calculation on the O mass spectrum signal to obtain delta of moisture in the vegetable and fruit sample 17 O value and delta 18 O value.
The application provides an oxygen isotope determination method which is a method for determining the oxygen isotope ratio information in water in vegetables and fruits, comprising the steps of firstly crushing a vegetable and fruit sample, heating and distilling to obtain distilled liquid distilled from the vegetable and fruit sample, adding silver salt and an organic solution containing elemental iodine into the distilled liquid for disproportionation reaction, and based on elemental iodine I 2 Can be disproportionated with water to produce I - And IO (input/output) 3 - While the added silver salt provides Ag + And I - Formation of AgI precipitate, thus IO can be controlled 3 - Is produced, and the collected water phaseThe solution contains the IO 3 - The method comprises the steps of carrying out a first treatment on the surface of the Subsequent detection of IO in the aqueous solution using high resolution mass spectrometry 3 - The obtained oxygen isotope mass spectrometry information comprises: IO (input/output) 3 - A basal peak, 17 O mass spectrum signal 18 O mass spectrum signal, calculate isotope ratio to obtain delta of moisture in vegetable and fruit sample 17 O value and delta 18 O value. The application can realize the effect of separating vegetable and fruit water 17 O and 18 o is measured simultaneously, the detection speed is high, and the result is accurate, so that the method has good application prospect.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic illustration of an embodiment of the present application 17 O and 18 an O stable isotope mass spectrogram;
FIG. 2 is a schematic illustration of an embodiment of the present application 17 Isotope ratio operating diagram of O;
FIG. 3 is a schematic illustration of an embodiment of the present application 18 Isotope ratio operating graph of O.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
In the present application, the term "and/or" describes an association relationship of an association object, which means that three relationships may exist, for example, a and/or B may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.
In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s).
It should be understood that, in various embodiments of the present application, the sequence number of each process described above does not mean that the execution sequence of some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The weights of the relevant components mentioned in the description of the embodiments of the present application may refer not only to the specific contents of the components, but also to the proportional relationship between the weights of the components, so long as the contents of the relevant components in the description of the embodiments of the present application are scaled up or down within the scope of the disclosure of the embodiments of the present application. Specifically, the mass described in the description of the embodiment of the application may be a mass unit known in the chemical industry field such as [ mu ] g, mg, g, kg.
The terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated for distinguishing between objects such as substances from each other. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.
In the embodiment of the present application, the high-resolution mass spectrum (high resolution mass spectrum) detection is a mass spectrum technique generally measured by a mass spectrometer with a resolution of 30000 or more.
In addition, the oxygen isotope ratio information measured in the examples of the present application includes delta 17 O value and delta 18 O value: delta 17 O(δ- 17 O) refers to the ratio of two oxygen stable isotopes: 17 O： 16 the thousandth deviation of the corresponding ratio of O to the standard (standard sample). Delta 18 O(δ- 18 O) refers to the ratio of two oxygen stable isotopes: 18 O： 16 the thousandth deviation of the corresponding ratio of O to the standard (standard sample).
The method for researching the rapid and accurate determination of the oxygen stable isotope ratio in the agricultural products has very important significance for establishing an oxygen stable isotope database of the agricultural products, constructing a production place traceability system, protecting geographic mark products, realizing food label regulation and guaranteeing food safety.
The current oxygen stable isotope ratio determination of moisture is mainly based on Isotope Ratio Mass Spectrometry (IRMS) detection, which not only consumes a long time, but also has interfered detection results, and is difficult to determine simultaneously 17 O and 18 O。
in recent years, organic high-resolution mass spectrometers have been used for stable isotope determination of anions in samples of the environment, living things, and the like. The high-resolution mass spectrometer has high mass resolution, can distinguish various isotope peaks of a substance to be detected through accurate measurement of molecular weight, and has the advantages of high sample analysis speed, simplicity, convenience and rapidness in operation, high precision, good accuracy and the like.
Based on the above consideration, in order to overcome the defects of easy interference, long time consumption and low sensitivity in the existing Isotope Ratio Mass Spectrometry (IRMS) detection technology, the embodiment of the application develops and researches a method for realizing the effect of the detection of the water content of vegetables and fruits 17 O and 18 o is measured simultaneously, fast and accurately. The specific method is as follows.
The embodiment of the application provides an oxygen isotope determination method, which comprises the following steps:
s01: crushing a vegetable and fruit sample, and then performing heating treatment to obtain distilled liquid distilled from the vegetable and fruit sample;
s02: adding silver salt and an organic solution containing elemental iodine into the distillate to perform disproportionation reaction, and then collecting an aqueous phase solution;
s03: for IO in aqueous phase solution 3 - Performing high-resolution mass spectrometry detection to obtain oxygen isotope mass spectrometry information;
s04: IO from oxygen isotope mass spectrometry information 3 - A basal peak, 17 O mass spectrum signal 18 Performing isotope ratio calculation on the O mass spectrum signal to obtain delta of moisture in the vegetable and fruit sample 17 O value and delta 18 O value.
The chemical equation of the reaction principle involved in the embodiment of the application is as follows:
3I 2 + 3H 2 O + 5Ag + = 5AgI↓ + 6H + + IO 3 - 。
according to the embodiment of the application, the vegetable and fruit sample is crushed, heated and distilled to obtain distilled liquid distilled from the vegetable and fruit sample, and then silver salt and an organic solution containing elemental iodine are added into the distilled liquid to perform disproportionation reaction, based on elemental iodine I 2 Can be disproportionated with water to produce I - And IO (input/output) 3 - While the added silver salt provides Ag + And I - Formation of AgI precipitate, thus IO can be controlled 3 - And the collected aqueous phase solution contains the IO 3 - The method comprises the steps of carrying out a first treatment on the surface of the Subsequent detection of IO in the aqueous solution using high resolution mass spectrometry 3 - The obtained oxygen isotope mass spectrometry information comprises: IO (input/output) 3 - A basal peak, 17 O mass spectrum signal 18 O mass spectrum signal, calculate isotope ratio to obtain delta of moisture in vegetable and fruit sample 17 O value and delta 18 O value. The application can realize the effect of separating vegetable and fruit water 17 O and 18 o is measured simultaneously, the detection speed is high, and the result is accurate, so that the method has good application prospect.
Step S01 is a stage of preparing vegetable and fruit samples.
In some embodiments, the vegetable and fruit samples include vegetables and fruits which are commonly used at present and contain moisture, and particularly all samples which contain moisture, such as at least one of Chinese cabbage, tomatoes, cucumbers, apples, pears and cherries.
Specifically, the vegetables or fruits containing moisture are left in the shade at room temperature (25-27 ℃) for airing, so that the interference of external moisture is avoided. Homogenizing vegetable and fruit samples by a homogenizer, taking a certain amount of homogenized samples in a round bottom flask, introducing inert atmosphere gas to remove the interference of water vapor possibly existing in a pipeline, evaporating the water content of the samples by a distillation device, and collecting distillate. The first approximately 5mL distillates can be removed during collection to reduce the possibility of impurity interference.
In some embodiments, the ratio of the weight of the vegetable and fruit sample to the volume of distillate obtained from the heated distillation is 50-500g:0.05-10 mL. Under the condition of the proportion, the oxygen of the water to be detected in the vegetable and fruit sample can be well obtained.
In some embodiments, the temperature of the heat treatment may be 80-200 ℃; the water can be well evaporated under the temperature condition.
Step S02 is a disproportionation reaction stage.
Based on Ag + Regulation I 2 Disproportionation reaction in water to produce IO 3 - Can effectively convert oxygen isotope in water into IO 3 - And (5) measuring oxygen isotopes.
In some embodiments, in the step of adding silver salt and the organic solution containing elemental iodine to the distillate, the silver salt is added in an amount of 0.5 mM to 3.0 mM of the silver ion concentration of the system after the addition of the silver salt. The silver salt may be added as a solid or as a silver salt solution. The purity of the silver salt is not less than 99 percent and does not contain crystal water; the silver salt solution can be prepared by adding a certain amount of silver salt solution or silver salt solid according to the sample amount by using an organic reagent (such as acetonitrile) without containing moisture, so that Ag in the reaction system solution + The concentration of the ions is not lower than 0.2 mM mM, specifically 0.2 mM-50 mM, for example, 0.5 mM, 2.0 mM, 3.0 mM, 5.0 mM, 10 mM, 15 mM, 20 mM, 30 mM, 40 mM, etc., and silver ions in the above concentration ranges can sufficiently undergo disproportionation reaction with water molecules. The amount of silver salt added can be adjusted according to the sensitivity of the instrument.
In some embodiments, the silver salt includes at least one of a nitrate salt and silver acetate.
In some embodiments, the ratio of the molar amount of elemental iodine to the silver salt is greater than 3:5. according to the chemical equation of the reaction principle, silver ions can be fully reacted under the condition of the molar ratio.
In some embodiments, the organic solvent is selected from at least one of carbon tetrachloride, chloroform, methylene chloride, benzene, and n-hexane in the organic solution containing elemental iodine. The purity of the iodine simple substance and the organic solvent used for dissolving the iodine simple substance is not lower than 99.9%, the used organic solvent is not mutually soluble with water, so that two phases are formed after disproportionation reaction, and IO to be detected is obtained 3 - Is in an aqueous phase solution. Adding excessive iodine simple substance into the organic solution containing simple substance iodine to prepare saturated solution.
Adding silver salt and an organic solution containing elemental iodine into the distillate, and carrying out vortex oscillation for 1-5 min to promote part I 2 Entering a water phase to perform disproportionation reaction; trace I in solution - With Ag + Rapidly generating AgI precipitate to quantitatively generate IO 3 - . The aqueous phase solution obtained can be centrifuged or filtered to remove insoluble substances.
Step S03 is a mass spectrometry detection phase.
Oxygen isotope information in moisture from vegetable and fruit samples can be obtained by high-resolution mass spectrometry.
In some embodiments, for IO in aqueous solution 3 - Before mass spectrometry detection, methanol or acetonitrile is added into the aqueous phase solution for dilution treatment. Methanol or acetonitrile purity is chromatographic purity and above, the dilution factor of the sample may be determined according to the respective use and instrument conditions, specifically, the volume ratio of the aqueous phase solution to methanol or acetonitrile is (1:99) - (50:50), and illustratively, the volume ratio may be 5:95, 10:90, 20:80, 30:70, 40:60, 50:50, etc.; for example, in one embodiment of the present application, the amount of aqueous solution is 50. Mu.L and the amount of methanol or acetonitrile added is 950. Mu.L.
In some embodiments, high resolution mass spectrometry detectionDetecting by a mass spectrometer with an electrospray ion source, wherein the mass spectrum resolution is more than or equal to 30000, for example, the mass spectrum resolution is more than or equal to 70000; the acquisition parameters of the mass spectrometer are as follows: electrospray ion source, negative ion detection; sample injection mode: needle pump sample injection, scanning m/z range of 170-182, and detecting material IO 3 - 。
By using electrospray high resolution mass spectrometry for isotope determination, oxygen isotope ratio information in moisture can be better obtained. In addition, the accurate discrimination capability of electrospray high-resolution mass spectrum and the simple and rapid operation realize the vegetable and fruit oxygen isotope @ and @ the 17 O and 18 o) the single sample analysis time is about 1.0 h, which is greatly shortened compared with the traditional IRMS analysis time (about tens of hours), the required sample amount is small (about tens of microliters), and the method is suitable for the rapid determination of large-scale samples.
Step S04 is a mass spectrometry information processing stage.
FIG. 1 shows the IO obtained after the instrument collects the relevant signals 3 - A mass spectrum, comprising 17 O and 18 o isotope mass spectrometry signal. IO from oxygen isotope mass spectrometry information 3 - Base peak (base peak), 17 O mass spectrum signal 18 The isotope ratio calculation of the O mass spectrum signal can be performed by calculating the water content in the sample through a standard curve 17 O and 18 delta value of O. Specifically, δ 17 O value and delta 18 The correction curves for the O values (see fig. 2 and 3) are: and (3) taking the isotope ratio of the standard water sample as an abscissa and the delta value of the standard water sample as an ordinate to form a linear fitting curve.
In summary, embodiments of the application are based on Ag + Regulation I 2 Disproportionation reaction in water to produce IO 3 - Can effectively convert the oxygen isotope measurement in the vegetable and fruit water into IO 3 - Measuring an oxygen isotope; the controllability of disproportionation reaction is realized through silver salt, thereby quantitatively generating IO 3 - The method comprises the steps of carrying out a first treatment on the surface of the Accurate discrimination capability through high-resolution mass spectrum and simple and rapid operation, and realizes that vegetable and fruit water is contained 17 O and 18 and O is detected rapidly and accurately at the same time.
The following description is made with reference to specific embodiments.
Example 1
An oxygen stable isotope determination of moisture in apples, comprising the steps of:
(1) Airing apples at a shade place at room temperature, taking a 500g apple sample, and uniformly stirring by a refiner; the 300 g homogenized sample was then weighed and subjected to moisture distillation in a round bottom flask. Ar gas is introduced for 5 min before distillation, and the water vapor interference possibly contained in a pipeline is removed; before collecting the distillate, about 5mL of the first distillate was removed, and then 5mL distillate was collected.
(2) Excess I 2 Dissolving in carbon tetrachloride solution to obtain saturated I 2 A carbon tetrachloride solution; weigh 170 mg AgNO 3 The solid is prepared into AgNO with the concentration of 100 mM by using chromatographic pure acetonitrile to reach the constant volume of 10.0 mL 3 Acetonitrile solution.
Taking the distilled liquid obtained in the step (1) of 1.0 mL, adding 20 mu L of prepared AgNO 3 Shaking acetonitrile solution, adding 1.0 mL to prepare I 2 The carbon tetrachloride solution was vortexed for 3 min and centrifuged at 9000 rpm for 5 min. 50.0 mu L of the aqueous phase solution of the supernatant is taken, 950 mu L of chromatographic pure methanol is added, and the mixture is shaken uniformly to obtain a sample solution to be detected.
(3) Injecting the sample solution to be detected obtained in the step (2) into a four-stage rod-orbitrap high-resolution mass spectrum (highest resolution 120000) at a flow rate of 20 mu L/min by adopting a needle pump sample injection mode, adopting electrospray anion detection, scanning an m/z range of 170-182, and carrying out IO (input/output) in the sample solution to be detected 3 - And (5) detecting.
(4) Processing the detection data, and respectively extracting IO 3 - A base peak of (C), 17 O and 18 mass spectrum signal of O, calculating isotope ratio, using standard substance (water) with oxygen isotope fixed value as standard curve, calculating water content in apple sample according to the curve 17 O and 18 delta value of O.
Accuracy evaluation: a standard curve is established by adopting 3 water standard substances ER2A, ER4E, ER E, delta of three standard substances 17 O and delta 18 O is respectively as follows: ER2A (delta) 17 O=9.13‰，δ 18 O=23.00‰），ER4E（δ 17 O= -4.12‰，δ 18 O= -7.81‰），ER3E（δ 17 O= -5.83‰，δ 18 O= -11.04% 17 O= -1.52‰，δ 18 O= -2.99%o) delta 17 O and delta 18 O, the measurement result is: delta 17 O= -1.42‰，δ 18 O= -3.15%o, the deviations from the given values are respectively: delta 17 O is-0.10 per mill; delta 18 O is 0.16 per mill, and the accuracy of the result is high.
Actual sample measurement: two different source apple samples were assayed separately, one from chile and the other from south africa, chile apple assay: delta 17 O= -0.63、δ 18 O=1.60, south african apple measurement: delta 17 O= -4.11、δ 18 O= -3.41. The results show that the apple delta is derived from different places 17 O、δ 18 Obvious difference of O, delta 17 O、δ 18 O has a very good differentiation.
The above results indicate that the one-time measurement of the moisture-containing oxygen isotope contained in the apple sample can be simultaneously measured by the method of this example 17 O and 18 the analysis speed is high (the whole period of a single sample is about 1 h), the detection efficiency is improved by tens of times compared with that of the traditional IRMS method (tens of hours), the detection result accuracy is good (within 0.20 per mill), and the method can be used for identifying fruits in different producing areas (sources).
Example 2
An oxygen stable isotope determination of moisture in tomatoes, comprising the steps of:
(1) Airing tomatoes at a shade place at room temperature, taking about 500 and g samples, and uniformly stirring by a refiner; the 200 g homogenized sample was weighed and subjected to moisture distillation in a round bottom flask. Ar gas is introduced for 5 min before distillation, and the water vapor interference possibly contained in a pipeline is removed; before collecting distillate, removing about 5mL of the first distillate, and collecting 5mL distillate;
(2) Excess I 2 Dissolving in chloroform solution to obtain saturated solutionI 2 A chloroform solution; adding 0.501 mg silver acetate (AgAc) into the distilled liquid obtained in the step (1) of 3.0 mL to dissolve and shake uniformly, and adding 3.0 mL to prepare I 2 The chloroform solution is vortexed for 3 min, 2.0 mL aqueous phase solution is taken and filtered through a 0.22 mu m aqueous phase filter membrane. And taking 100 mu L of filtrate, adding 900 mu L of chromatographic pure acetonitrile, and shaking uniformly to obtain a sample solution to be detected.
(3) Injecting the sample solution to be detected obtained in the step (2) into a four-stage rod-orbitrap high-resolution mass spectrum (highest resolution 120000) at a flow rate of 10 mu L/min by adopting a needle pump sample injection mode, adopting electrospray anion detection, scanning an m/z range of 170-182, and performing reaction to generate IO (input/output) 3 - And (5) detecting.
(4) Processing the detection data, and respectively extracting IO 3 - A base peak of (C), 17 O and 18 mass spectrum signal of O, isotope ratio calculation, standard substance (water) with oxygen isotope fixed value is adopted as standard curve, and the moisture content in the sample is calculated according to the curve 17 O and 18 delta value of O.
Accuracy evaluation: establishing standard curve by using 3 water standard substances GB04458, GB04459 and GB04461, and delta of the three standard substances 18 O is respectively as follows: GB04458 (delta) 18 O= -0.15‰），GB04459（δ 18 O= -8.61‰）, GB04461（δ 18 O= -55.73% 18 O= -19.13%o) delta 18 O, measurement result is delta 18 O= -18.50%: -0.63%o, the relative variation is-3.3%, and the result accuracy is good.
Actual sample measurement: two domestic tomato samples from different sources, one from Huizhou and the other from Xinjiang, huizhou tomato measurements were measured: delta 18 O= -2.85, measurement of tomato in Xinjiang: delta 18 O= -6.79. The results show that the tomatoes delta from different sources 18 The difference of O is obvious, and the method has good differentiation.
The above results indicate that the analysis speed of the moisture oxygen isotope contained in the tomato sample is measured by the method of this exampleThe method is quick (only about 1 h is needed for sample pretreatment and measurement), has good detection result accuracy (relative deviation is-3.3%), and can be used for identifying fruits in different producing areas (sources). Of course, this example only verifies the measured delta 18 O accuracy, the oxygen isotope content in tomato samples can be measured at the same time 17 O and 18 O。
the foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.
Claims (10)
1. An oxygen isotope measurement method comprising:
crushing a vegetable and fruit sample, and then performing heating treatment to obtain distilled liquid distilled from the vegetable and fruit sample;
adding silver salt and an organic solution containing elemental iodine into the distillate to perform disproportionation reaction, and then collecting an aqueous phase solution;
for IO in the aqueous phase solution 3 - Performing high-resolution mass spectrometry detection to obtain oxygen isotope mass spectrometry information;
IO from the oxygen isotope mass spectrometry information 3 - A basal peak, 17 O mass spectrum signal 18 Performing isotope ratio calculation on the O mass spectrum signal to obtain delta of moisture in the vegetable and fruit sample 17 O value and delta 18 O value.
2. The method for measuring oxygen isotopes according to claim 1, wherein in the step of adding a silver salt and an organic solution containing elemental iodine to the distillate, the addition amount of the silver salt is calculated in such a manner that the silver ion concentration of the system after the addition of the silver salt is 0.2 mM-50 mM.
3. The oxygen isotope determination method of claim 1 wherein the molar ratio of elemental iodine to silver salt is greater than 3:5.
4. the oxygen isotope determination method of claim 1 wherein the silver salt includes at least one of nitrate and silver acetate.
5. The oxygen isotope determination method according to claim 1, wherein the organic solvent in the elemental iodine-containing organic solution is at least one selected from the group consisting of carbon tetrachloride, chloroform, methylene chloride, benzene and n-hexane.
6. The oxygen isotope determination method according to claim 1, wherein for IO in the aqueous phase solution 3 - Before mass spectrometry detection, methanol or acetonitrile is added into the aqueous phase solution for dilution treatment.
7. The oxygen isotope assay method of claim 6 wherein the volume ratio of the aqueous solution to the methanol or acetonitrile is from (1:99) to (50:50).
8. The oxygen isotope determination method according to any one of claims 1-7, wherein the high resolution mass spectrometry detection is performed by a mass spectrometer equipped with an electrospray ion source, and the mass spectrometry resolution is equal to or higher than 30000, and the mass spectrometer acquisition parameters are: electrospray ion source, negative ion detection; sample injection mode: needle pump sample injection, scanning m/z range of 170-182, and detecting material IO 3 - 。
9. The method according to any one of claims 1 to 7, wherein the ratio by volume of the vegetable and fruit sample to the distillate obtained is 50-500g:0.05-10 mL.
10. The oxygen isotope assay method according to any one of claims 1 to 7, wherein the vegetable and fruit sample is a moisture-containing sample including at least one of cabbage, tomato, cucumber, apple, pear, and cherry.
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