Method for Simultaneous Determination of Nitrogen and Oxygen Isotopic Composition of Natural Nitrate and Nitrite

Abstract

The invention discloses a method for simultaneously measuring the composition of natural nitrate and nitrite nitrogen and oxygen isotopes, quantitatively converting nitrate and nitrite into corresponding organic esters and nitro compounds, and then adopting gas chromatography / pyrolysis / Simultaneous Determination of Nitric Acid and Nitrite δ by Gas Chromatography / Isotope Ratio Mass Spectrometry 18 O and delta 15 N determination. The method for simultaneously measuring the nitrogen and oxygen isotope composition of natural nitrate and nitrite of the present invention requires less sample consumption and does not cause loss, gain, exchange and fractionation of nitrogen and oxygen.

Description

technical field [0001] The invention belongs to the technical field of isotope determination, in particular to a method for simultaneously determining the nitrogen and oxygen isotopic compositions of natural nitrate and nitrite. Background technique [0002] Techniques for measuring the oxygen and nitrogen isotopic composition of nitrates and nitrites are frequently used to trace and identify nitrogen sources and biological, terrestrial, and chemical transformations (eg, nitrification, denitrification) in environmental and living systems. The isotopic composition of an element is usually expressed by δ: δ=(R sample / R standard ﹣1)×1000, where R is the abundance ratio of the heavy isotope to the light isotope of an element (eg: 18 O / 16 O, 15 N / 14 N), the subscripts sample and standard represent the sample and the international standard of the element, respectively. Oxygen and nitrogen isotope ratios are expressed as δ 18 O and delta 15 N. [0003] Currently, nitrat...

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Problems solved by technology

[0004] The ion exchange-silver nitrate method has the following disadvantages: 1) In order to obtain high-purity AgNO 3 and AgNO 2 For reliable isotope analysis, lengthy sample processing must be performed to eliminate the interference of other nitrogen-containing and oxygen-containing salts; 2) Nitrate and nitrite cannot be separated, and a mixed δ containing nitrate and silver nitrite is obtained 18 O and delta 15 N value; 3) AgNO 3 and AgNO 2 Large dosage (usually more than 0.2mg pure sample), need to collect and process a large number of samples to obtain enough AgNO 3 and AgNO 2 For testing; 4) Not suitable for high-salinity samples such as seawater; 5) It is impossible to inject one sample and obtain δ at the same time 18 O and delta 15 N's purpose

[0005] The bacterial denitrification method has the following disadvantages: 1) Bacterial culture facilities and skills are required; 2) This method is not suitable for samples containing toxic denitrifying bacteria such as heavy metals or pesticides; 3) The conversion of nitrate and nitrite into N 2 The O process will cause 5 / 6 and 2 / 3 oxygen loss respectively, and the direct analysis object N 2 Part of O in O undergoes isotope exchange with O in the reaction system, and nitrate and nitrite are converted into N 2 O conversion rate is not high, resulting in nitrogen and oxygen isotopic fractionation, can not obtain accurate and reliable δ 18 O and delta 15 N; 4) At least two bacterial denitrifications are required to achieve the determination of the respective δ of nitrate and nitrite 18 O and delta 15 N purpose; 5) It is impossible to achieve a sample injection and obtain δ at the same time 18 O and delta 15 N's purpose

[0006] The cadmium / azide reduction method has the following disadvantages: 1) the sodium azide used in this method is highly toxic and explosive; 2) nitrate and nitrite are simultaneously reduced to N 2 O, the obtained δ 18 O and delta 15 N includes mixed contributions from nitrate and nitrite; 3) Similar to technique ②, nitrate is reduced to N 2 O process has 2 / 3 oxygen loss, direct analysis object N 2 Part of O in O undergoes isotope exchange with O in the reaction system, 1 / 2 of N comes from azide (acid), and nitrate is converted into N 2 O conversion rate is not high, resulting in nitrogen and oxygen isotopic fractionation, can not obtain accurate and reliable δ 18 O and delta 15 N; 4) The highly reactive "cadmium sponge" used needs to be prepared in advance; 5) δ 18 O measurement has serious pH dependence; 6) If IRMS is used for isotope determination, it is impossible to achieve a single injection and simultaneously obtain δ 18 O and delta 15 The purpose of N; 7) Not suitable for high salinity samples (such as seawater, etc.)

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