CN112285246A

CN112285246A - Method for detecting pollutants in salt

Info

Publication number: CN112285246A
Application number: CN202011584464.3A
Authority: CN
Inventors: 张驰; 吴肖肖; 杨淼; 梅秀明; 蒋迪尧; 张露; 顾慧丹; 乔玲; 纪晗旭; 王灿
Original assignee: NANJING INSTITUTE OF PRODUCT QUALITY INSPECTION
Current assignee: NANJING INSTITUTE OF PRODUCT QUALITY INSPECTION
Priority date: 2020-12-29
Filing date: 2020-12-29
Publication date: 2021-01-29
Anticipated expiration: 2040-12-29
Also published as: CN112285246B

Abstract

The invention discloses a method for detecting pollutants in salt, belonging to the technical field of analysis and detection. The method comprises the steps of uniformly mixing a salt sample to be detected with water, then sending the mixture into a solid phase microextraction and gas chromatography-mass spectrometry combined system for non-targeted scanning of pollutants, carrying out qualitative detection on the detected substances by an NIST database, and further carrying out quantitative detection by adopting an external standard method. By adopting the method, 3 chemical pollutants of dibutylamine, N-dibutylformamide and N, N-dibutylacetamide are found in the salt with the peculiar smell, and 3 newly found chemical pollutants are quantified.

Description

Method for detecting pollutants in salt

Technical Field

The invention belongs to the technical field of analysis and detection, and particularly relates to a method for detecting pollutants in table salt by using solid-phase microextraction (SPME) and gas chromatography-tandem mass spectrometry (GC-MS/MS).

Background

Common salt is the most popular seasoning in life and is rarely polluted by chemical substances. However, a large amount of odoriferous rock salt has been on the market, and when rubbed by hand, it emits a strong sweaty foot odor and is therefore called "smelly foot salt".

What odor components exist in the smelly foot salt and whether the smelly foot salt and the odor components threaten the health of human bodies are the key problems of the smelly foot salt. Although there are reports claiming the detection of nitrite and hydrogen sulfide, the official conclusion is that this odor is a naturally occurring short-chain fatty acid (SCFAs) of rock salt minerals, which is not harmful to human health and even beneficial to the gastrointestinal tract. Additional investigators used headspace gas chromatography-mass spectrometry (HS-GC/MS) to screen for components in "skatole salt" by querying the National Institute of Standards and Technology (NIST) database to identify 5 and 13 different SCFAs from salt and raw brine, respectively. Currently, there is no correlation study to show whether other contaminants are present in "skatole salts".

Disclosure of Invention

In view of the above disadvantages of the prior art, the present invention provides a method for detecting contaminants in salt by using solid-phase microextraction (SPME) and gas chromatography-tandem mass spectrometry (GC-MS/MS).

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for detecting contaminants in table salt, comprising the steps of:

step 1, sample preparation: weighing a salt sample to be detected, adding water, and uniformly mixing;

step 2, sending the mixture obtained in the step 1 into a solid phase microextraction and gas chromatography-mass spectrometry combined system for non-targeted scanning of pollutants;

step 3, performing qualitative determination on the substances detected in the step 2 by an NIST database, performing confirmation by using standard substances based on retention time and characteristic fragment ions, selecting substances which have a matching score of more than 90%, have an obvious response and are weakly alkaline in aqueous solution, and further performing quantitative determination by adopting an external standard method;

the conditions of the solid phase microextraction are as follows:

fiber type: DVB/CWR/PDMS

Extraction temperature: 100 deg.C

Extraction time: 5 min

Rotating speed: 250 rpm

Extraction time: 20 min

Desorption time: 2 min;

the conditions for the gas chromatography-mass spectrometry combination were as follows:

the chromatographic column is HP-5 MS with specification of 30 m × 0.32 mm × 0.25 μm

The split ratio is 10:1

Temperature rising procedure: at 40 deg.C for 2 min, 10 deg.C/min to 200 deg.C for 5 min, 10 deg.C/min to 280 deg.C for 2 min

Scanning mode: MS (Mass Spectrometry)₂；

The substances determined in step 3 are dibutylamine, N-dibutylformamide and N, N-dibutylacetamide.

Further, the mass of the water in the step 1 is 10% of the mass of the salt sample to be detected.

The method can detect various salt samples, such as various edible salts, such as sea salt, rock salt, well salt, bamboo salt, seaweed salt and the like.

Has the advantages that: the invention utilizes the combination of solid-phase microextraction (SPME) and gas chromatography-tandem mass spectrometry (GC-MS/MS), firstly uses fiber to carry out solid-phase microextraction on a salt sample, then uses the gas chromatography-tandem mass spectrometry to carry out detection, and carries out qualitative determination on the scanned substances by an NIST database through a full-scanning mode, uses standard substances to carry out confirmation based on retention time and characteristic fragment ions, identifies and confirms 3 new chemical pollutants of dibutylamine, N-dibutylformamide and N, N-dibutylacetamide according to the retention time and the fragment ions of the standard substances, and carries out quantification on the 3 new found chemical pollutants.

Drawings

FIG. 1 shows the MS of a stinky foot salt sample₂Total ion flow map in scan mode.

FIG. 2 is a mass spectrum of dibutylamine in a stinky-smelling salt sample.

FIG. 3 is a mass spectrum diagram of N, N-dibutylformamide in a skatole salt sample.

FIG. 4 is a mass spectrum of N, N-dibutylacetamide in a skatole salt sample.

Detailed Description

The invention is described in further detail below with reference to the figures and the specific examples, which should not be construed as limiting the invention. Modifications or substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit and scope of the invention. The experimental methods and reagents of the formulations not specified in the examples are in accordance with the conventional conditions in the art.

In order to solve the problem that the presence of contaminants other than SCFAs has not been confirmed in the current studies on "skunk salt", the inventors conducted investigations on a sample of "skunk salt" in the past, using commercially available purified salt as a control.

First, 10g of each of a "smelly foot salt" sample and a commercially available refined salt was taken, and kneaded to determine whether or not there was an offensive odor. As a result, the odor of the sample was heavy, and the commercially available refined salt had no odor.

Then, 10g of each sample was taken, dissolved in water until saturated, and the pH of the aqueous solution was measured. The results show that the aqueous "skatole salt" solution is weakly alkaline and has a pH greater than commercially available refined table salt, indicating that there may be alkaline contaminants or impurities in the "skatole salt" sample.

And finally, further carrying out non-target screening and analysis on the peculiar smell salt and the reference salt by adopting solid phase microextraction and gas chromatography-tandem mass spectrometry. Respectively taking a smelly foot salt sample and a control salt sample, firstly carrying out micro-extraction on the samples by using a DVB/CWR/PDMS solid phase micro-extraction fiber head, and then carrying out MS (mass spectrometry) by using a gas chromatography-mass spectrometer₂And (6) scanning. MS in preliminary experiments when samples were not spiked with water₂The responses of two samples are not obviously different when being scanned, and the peak areas of a plurality of substances with high responses in the odorous foot salt sample are obviously reduced when the water adding amount is larger, so that pure water with the mass of 10% of that of the sample is added in the sample for experiment during actual detection.

Specifically, the method comprises the following steps:

the solid phase micro-extraction conditions were as follows: extraction temperature: 100 ℃; extraction time: 5 min; rotating speed: 250 rpm; extraction time: 20 min; desorption time: and 2 min.

The conditions for the gas chromatography-mass spectrometry combination were as follows: the chromatographic column is HP-5 MS with the specification of 30 m multiplied by 0.32 mm multiplied by 0.25 mu m; the split ratio is 10: 1; temperature rising procedure: at 40 ℃ for 2 minutes, 10 ℃/min to 200 ℃ for 5 minutes, 10 ℃/min to 280 ℃ for 2 minutes.

Comparing and analyzing unknown compounds scanned from the odorous foot salt sample and the control salt sample by adopting a NIST spectrogram library, selecting substances which have matching scores of more than 90, do not exist in the control salt sample, have obvious strength in the odorous foot salt and are alkaline in aqueous solution, and finding three compounds of dibutylamine, N-dibutylformamide and N, N-dibutylformamide. MS (Mass Spectrometry)₂The total ion flow under the scanning mode is shown in figure 1, and the mass spectrograms of the three scanned compounds are respectively shown in figures 2-4. Further detecting the three compounds as standard substances under the same chromatographic mass spectrum conditionCompounds were validated by comparing retention time and fragment ions.

Through previous experiments of the inventor, 3 chemical pollutants of dibutylamine, N-dibutylformamide and N, N-dibutylacetamide are detected in a plurality of batches of 'skatole' samples, and then 3 newly found chemical pollutants are further quantitatively analyzed.

Example 1

Weighing 4 g of sodium chloride, adding 400 mu L of pure water, adding a series of dibutylamine, N-dibutylformamide and N, N-dibutylacetamide standard solutions to prepare a series of concentration gradients, establishing an external standard method standard curve based on SPME-GC-MS/MS combined detection, and inspecting the linearity and range of a newly-built method, wherein specific results are shown in Table 1.

TABLE 1 Linear equation, correlation coefficient, linear range, detection limit, and quantification limit for three chemical pollutants

From the above results, it is found that the linear relationship is good when dibutylamine is in the concentration range of 1.25 to 50.0. mu.g/kg, N-dibutylformamide is in the concentration range of 0.250 to 50.0. mu.g/kg, and N, N-dibutylacetamide is in the concentration range of 0.0620 to 50.0. mu.g/kg.

Example 2

Weighing 4 g of blank salt as a matrix, adding 400 mu L of pure water, adding a mixed standard of three substances of dibutylamine, N-dibutylformamide and N, N-dibutylacetamide, wherein the concentrations are 1 mu g/kg, 10 mu g/kg and 50 mu g/kg respectively, and inspecting the standard addition recovery rate of the newly-established method based on SPME-GC-MS/MS combined instrument detection. The results are shown in Table 2.

TABLE 2 results of recovery measurements of three chemical contaminants with standard addition

According to the results, the standard recovery rate of the three substances is 98.3-105.5%.

Example 3

6 samples of "stinky foot salt" and 6 samples of control salt were weighed to obtain 4 g each, 400. mu.L of pure water was added, and the mixture was subjected to SPME-GC-MS/MS combination test, and the test results are shown in Table 3.

TABLE 3 results of detection of three contaminants in stinky foot salt and control salt samples

From the above results, three kinds of contaminants were not detected in the control common salt sample, and 2 or more kinds of contaminants were detected in the "stinky salt" sample.

Claims

1. A method for detecting contaminants in table salt is characterized in that: the method comprises the following steps:

step 2, sending the mixture obtained in the step 1 into a solid phase microextraction and gas chromatography-mass spectrometry combined system for non-targeted scanning;

step 3, the substances detected in the step 2 are qualitative by an NIST database, and further an external standard method is adopted for quantification;