Overview
On May 1, 2008, the Ministry of Health of the People's Republic of China promulgated the “Regulations on the Management of Food Nutrition Labels†[1] . All foods must be detailed in their food nutrients, nutritional claims and nutritional function claims. The specification requires mandatory testing and labeling of sodium and potassium, common nutrients in food.
The main purpose of formulating food nutrition label management methods is to guide and standardize the labeling of food nutrition labels of enterprises, guide consumers to rationally select foods, promote dietary nutrition balance, and protect people's health.
As a main test item for food nutrient analysis, sodium (Na) and potassium (K) detection methods
Including: inductively coupled plasma optical emission spectroscopy (ICP), atomic absorption spectrophotometry (AA) and flame photometry.
In the actual testing work, the ICP method and the AA method have many problems due to the slow detection speed and high daily consumption cost, which causes the laboratory to face a large number of daily food testing samples. The national standard test method for analysis is still flame photometry. GB/T5009.91-2003 "Determination of potassium and sodium in food" [2] .
GB/T5009.91-2003 "Determination of Potassium and Sodium in Foods" - Flame Emission Spectroscopy from the International Standard ISO 8070-1987 in 1987 "Determination of Sodium and Potassium in Milk Powder - Flame Emission Spectroscopy Law, the national standard method has experienced the development of GB12397-1990 "Method for the determination of potassium and sodium in food" in 1990, and the revision of GB/T5009.91-2003 "Determination of potassium and sodium in food" in 2003. Flame emission spectroscopy is always the standard method for elemental analysis of potassium and sodium.
Flame photometer
The flame photometer is an analytical instrument designed and manufactured based on the principle of flame emission spectroscopy. It mainly consists of an injector, an atomizer, a mixing chamber, a burner, a monochromator, and a photoelectric system.
1, flame stability
Flame is an important factor in the generation of atomic excitation, so flame stability is an important prerequisite for the accuracy of the flame photometer data. Since the optimal ratio of combustion gas to air is the key to flame stability, it is only possible to achieve accurate detection data by a flame photometer that achieves the best gas/air ratio.
2, calibration error
Pre-calibration of the analytical instrument is an important step in ensuring the accuracy of the analytical results. Due to human error, laboratory environment fluctuations (temperature, air pressure, wind speed, voltage, etc.) often introduce errors into the calibration of the instrument, only the flame photometer with calibration correction can effectively reduce the error in the calibration process to improve the accuracy of the analysis results. Sex
3, overrange error
Each sample analysis should be performed within the linear range of the flame photometer, otherwise the sample must be diluted or concentrated to ensure that its concentration is within the range. However, each dilution or concentration of the sample is a process of introducing errors, and the error is exponentially amplified with the number of dilutions or concentrations. Therefore, the selection of a super-large range of flame photometers is extremely meaningful for effectively reducing such errors;
4, reading error
The reading method of the flame photometer is divided into single point reading and continuous reading. According to statistical principles, the data for single-point readings is far less representative than the mean of consecutive readings. Therefore, the flame photometer with continuous reading can improve the accuracy of the data to a large extent.
Solving the error defect design of the flame photometer is the key to improve the detection accuracy, and it is also the problem that the current analysis users pay attention to in their respective application fields.
Modern flame photometer
The modern flame photometer has the following features:
1. Built-in air compressor design, each flame photometer is adjusted to the best gas/air ratio point by the manufacturer before leaving the factory to avoid the error caused by the external air compressor artificial adjustment;
2, built-in calibration correction function, can effectively avoid various random errors in the instrument calibration process;
3, the range of ultra-large range, the range of the range is 5 times that of other flame photometers, which can basically realize the sample liquid analysis to avoid the error caused by sample dilution and concentration;
4, continuous reading, using more than 20 consecutive readings per second, and automatically remove invalid readings, display the average reading, so that the test results are more accurate;
5, standard data management software, can automatically record the print test data and continuous reading curve, so that the test results record more comprehensive, the software meets the GLP specification;
6, can carry out IQ / OQ verification to meet high-end laboratory management requirements.
It fundamentally overcomes the design flaws that cause errors, and can provide efficient and accurate support in the application of potassium and sodium in food, and is a good solution for this test.
Reference material
· 3. A brief introduction to the flame photometry. cnki.net. 1957-06-11 [reference date 2013-05-22].
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