A method and device for rapid and automatic determination of melamine content in dairy products

Abstract

The invention discloses a rapid and automatic determination method and device for tripolycyanamide content in dairy products, belonging to the field of food analysis. The method comprises the following steps that: in a unit (A) under an operating procedure, a first step, a multifunctional valve is in a state I, a pump A rotates, a pump B stops, a first sample flows into a column 2 for enriching tripolycyanamide, and the eluent flows into a column 1 for regenerating tripolycyanamide; a second step, the pump A stops, the pump B rotates, the cleanout fluid flows into the column 2 for cleaning the impurities therein; a third step, the multifunctional valve is switched to a state II, eluent flows into the column 2 for eluting and regenerating tripolycyanamide; the tripolycyanamide in the column 2 is substituted by the eluent and directly enters into a sampling ring of a unit (B) in the form of a sample plug, so as to perform volume quantification, injection, re-separation and detection, and a response signal is processed by a computer; and meanwhile, a second sample enters into the column 1 for enrichment, and the process of the column 2 is repeated. The method and the device are high in automation degree and excellent in reproducibility, and can analyze about 30 samples per hour; and the unit (A) in the invention can be used with various flow injection analysis systems.

Description

technical field [0001] The invention relates to a method and a device for rapid and automatic determination of melamine content in dairy products, belonging to the field of food analysis. The present invention can also be used in conjunction with various flow injection analysis systems for rapid, accurate and automatic determination of melamine content in various dairy products. [0002] Background technique [0003] Melamine is a white odorless nitrogen-heterocyclic organic compound with a nitrogen content of 66.7%, which is about 4 times that of protein. Due to the current detection method for protein in dairy products—Kjeldahl method (J. Dairy Sci., 1978 , 61(7): 870-873) cannot distinguish between protein nitrogen and non-protein nitrogen, so some unscrupulous merchants add melamine to dairy products to increase the apparent protein content of dairy products. After melamine enters the human body, it will be gradually hydrolyzed to produce cyanuric acid, which will then...

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Problems solved by technology

[0003] Melamine is a white odorless nitrogen-heterocyclic organic compound with a nitrogen content of 66.7%, which is about 4 times that of protein. Due to the current detection method for protein in dairy products—Kjeldahl method (J. Dairy Sci., 1978 , 61(7): 870-873) cannot distinguish between protein nitrogen and non-protein nitrogen, so some unscrupulous merchants add melamine to dairy products to increase the apparent protein content of dairy products

[0008] The above-mentioned method has the following disadvantages: 1). The sample pretreatment process and the detection process are all manually operated, and the process is cumbersome, low in automation, large in human error, and poor in reproducibility (RSD<10%), so it cannot be applied to the rapid analysis of a large number of samples. Analysis; 2). The consumption of organic reagents during the cleaning and elution process of the mixed cation exchange solid phase extraction column is large, which not only endangers the health of analysts, but also increases environmental pollution; 3). Sample pretreatment process The detection process takes a long time and the analysis speed is slow, only 2~3 samples / h, which is not suitable for the rapid analysis of large quantities of dairy product samples; 4). The eluate flowing out of the extraction column cannot be directly measured, and it needs to be dried first Dissolving after treatment will not only cause the organic solvent to volatilize and pollute the environment, but also increase the pretreatment time of the sample and affect the overall analysis speed; 5). The solid phase extraction columns are all disposable, which not only greatly increases the Determination cost (extraction column price: 10-15 yuan / piece), waste treatment cost and waste of resources, but also increases the error source of pre-treatment, and ultimately affects the accuracy and precision of the analysis method; 6). The flow direction of the collection and sample elution liquid can only be in the same direction, so that the eluent flows through the extraction column and the time for elution of melamine increases, and the concentrated melamine is diluted again, which eventually leads to a decrease in ion exchange efficiency and a decrease in measurement sensitivity

However, the disadvantages of this method are: 1) The sample still needs to be pre-treated by cation-exchange solid-phase extraction, and it is a manual operation, which is cumbersome and has large errors; 2) The pre-treatment time is 40 minutes, and the enzyme-catalyzed reaction time is 10-15 minutes , the color reaction time is 30min, so the analysis takes too long (80min / sample), and the rapid determination of batch samples cannot be realized; 3) The column cleaning solution contains acetic acid, which will elute part of the melamine in the extraction column in the cleaning solution lost; in addition, Na + The ion exchange capacity is less than that of -NH 3 + , so the amount of melamine eluted by Na-MOPS eluent is less, which will reduce the sensitivity of the determination; 4) The enzyme reagent used is expensive and the analysis cost increases, which is not conducive to the popularization and application of the method

However, the disadvantages of these two methods are: 1) The pretreatment process is still manual operation; 2) In addition to melamine, some organic impurities in the sample still enter the test solution through the extraction membrane, which cannot achieve high selectivity for melamine The purpose of extraction; 3) The amount of sample is large; 4) The membrane extraction time is long (140min / sample), and the analysis speed is slow; 5) The solvents such as n-octanol and toluene used in the extraction process are highly toxic and harmful to health and the environment

The disadvantages of this method are: 1) The analysis speed is slow, only 2 samples h -1 ; 2) The flow rate of the extraction process is too small (0.1mL min -1 ), so that a large amount of organic impurities are also adsorbed in the extraction column during the extraction of melamine, which cannot achieve the purpose of highly selective extraction of melamine; 3) The elution flow rate is too low (0.1mL min -1 ), causing a large amount of organic impurities in the extraction column to be eluted into the chromatographic column, which not only affects the measurement results, but also affects the service life of the chromatographic column; 4) The flow rate of the mobile phase changes rapidly during valve B sampling, which will cause the stability of the measurement system to change. Poor, chromatographic system pressure fluctuations, affecting the life of the instrument and chromatographic column; 5) The eluent is an acidic environment (mobile phase pH 2.5), and the elution flow rate is only 0.1mL min -1 , therefore, the melamine cations exchanged during the elution process will be exchanged on the extraction column again, resulting in poor elution effect; 6) It is impossible to realize the parallel use of multiple columns to achieve faster analysis speed; 7) The extraction speed is slow and the elution There are many impurities in the dehydration, so it is difficult to combine with the measurement system other than chromatography, and the application range is narrow

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