Determination of Potassium and Sodium in Foods by Flame Atomic Absorption Spectroscopy
Determination of Potassium and Sodium in Foodstuffs in accordance with GB 5009.91-2017.
Principle
Following digestion, the sample is introduced into an atomic absorption spectrometer. Upon flame atomisation, potassium and sodium absorb at resonance lines of 766.5 nm and 589.0 nm respectively. Within a defined concentration range, the absorbance values correlate directly with potassium and sodium content, enabling quantitative analysis through comparison with a standard series.
Reagents and Materials
All reagents used were of analytical grade, and water was of Grade II as specified in GB/T
6682.Nitric acid (HNO₃).
Perchloric acid (HClO₄).
Cesium chloride (CsCl).
Potassium chloride standard (KCl): Purity greater than 99.99%.
Sodium chloride standard (NaCl): Purity greater than 99.99%.
Preparation of Standard Solutions
Potassium and Sodium Standard Stock Solutions (1000 mg/L): Dry potassium chloride or sodium chloride in an oven at 110°C to 120°C for 2 hours. Accurately weigh 1.9068 g of potassium chloride or 2.5421 g of sodium chloride, dissolve each in water, transfer to a 1000 mL volumetric flask, dilute to the mark, mix thoroughly, and store in polyethylene bottles at 4°C. Alternatively, use a standard solution certified by a national accreditation body and issued with a Certificate of Analysis.
Potassium and Sodium Standard Working Solutions (100mg/L): Accurately pipette 10.0mL of potassium or sodium standard stock solution into a 100mL volumetric flask. Dilute to the mark with water. Store in polyethylene bottles at 4°C.
Potassium and Sodium Standard Working Solutions: Accurately pipette 0 mL, 0.1 mL, 0.5 mL, 1.0 mL, 2.0 mL, and 4.0 mL of potassium standard working solution into a 100 mL volumetric flask. Add 4 mL of caesium chloride solution, dilute to the mark with water, and mix thoroughly. The potassium mass concentrations in this standard series working solution are 0 mg/L, 0.100 mg/L, 0.500 mg/L, 1.00 mg/L, 2.00 mg/L, and 4.00 mg/L respectively. The concentration range of the standard solution may also be adjusted appropriately based on the potassium concentration in the actual sample solution. Accurately pipette 0 mL, 0.5 mL, 1.0 mL, 2.0 mL, 3.0 mL, and 4.0 mL of sodium standard working solution into 100 mL volumetric flasks. Add 4 mL of caesium chloride solution, dilute to the mark with water, and mix thoroughly. The sodium mass concentrations in this standard working solution series are 0 mg/L, 0.500 mg/L, 1.00 mg/L, 2.00 mg/L, 3.00 mg/L, and 4.00 mg/L. Alternatively, the standard solution concentration range may be appropriately adjusted based on the sodium concentration in the actual sample solution.
Primary Instruments and Equipment
AA-1800C Atomic Absorption Spectrometer, equipped with a flame atomiser and potassium/sodium hollow cathode lamps. Analytical-grade acetylene cylinders and air compressor.
Microwave Digester
Analysis Steps
Microwave Digestion
Weigh 0.2 g to 0.5 g (accurate to 0.001 g) of the sample into the microwave digestion inner vessel. Samples containing ethanol or carbon dioxide should first be placed on the hotplate.
Heat gently to remove ethanol or carbon dioxide. Add 5 mL to 10 mL of nitric acid, cover, and allow to stand for 1 hour or overnight. Tighten the outer flask and place in a microwave digestion system for digestion (see Table A.1 for digestion conditions). After cooling, remove the inner vessel and place it on an adjustable temperature-controlled electric heating furnace. Evaporate the acid at 120°C–140°C until nearly dry, then dilute to a final volume of 25 mL or 50 mL with water. Mix thoroughly and set aside. Conduct a blank test simultaneously.
Instrument reference conditions
Optimise the instrument to its optimal state, with the primary conditions being: slit width 0.5 nm, lamp current 8 mA, and gas flow rate 1.2 L/min.
Preparation of the standard curve
Potassium and sodium standard series working solutions were injected into the atomic absorption spectrometer to determine their absorbance values. A standard curve was plotted with the concentration of the standard working solution on the x-axis and the absorbance value on the y-axis.
Determination of the Test Solution
Depending on the concentration of the element being measured in the sample solution, dilute the sample solution with water to an appropriate concentration where necessary. Add a measured volume of caesium chloride solution to both the blank solution and the final sample determination solution to achieve a caesium chloride concentration of 0.2%. Under identical experimental conditions to those for the standard calibration curve working solution, inject the blank solution and the test solution into the atomic absorption spectrometer to determine the absorbance values for potassium or sodium respectively. The concentration of potassium or sodium in the test solution is then obtained from the standard calibration curve.
The potassium and sodium content in the sample is calculated according to Equation (1):
In the formula:
X₁ - Content of the measured element in the sample, expressed in milligrams per hundred grams or milligrams per hundred millilitres (mg/100g or mg/100mL);
ρ - Mass concentration of the element in the test solution, expressed in milligrams per litre (mg/L);
ρ₀ - Mass concentration of the element in the blank test solution, expressed in milligrams per litre (mg/L);
V₁ represents the volume of the sample solution, expressed in millilitres (mL);
f denotes the dilution factor of the sample solution;
100.1 000 signifies the conversion factor;
m indicates the mass or volume of the sample, expressed in grams or millilitres (g or mL).
Conclusion: The absolute difference between two independent determinations obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. Based on a sample quantity of 0.5 g, diluted to 25 mL, the detection limit for potassium in this method is 0.2 mg/100 g, with a quantification limit of 0.5 mg/100 g; the detection limit for sodium
is 0.8 mg/100 g, with a quantification limit of 3 mg/100 g. The instrument detection limit of the AA-1800C atomic absorption spectrometer is lower than the method detection limits, thereby meeting the requirements of the method.
Instrument Specifications
AA-1800C Atomic Absorption Spectrometer
Instrument Application
Flame atomic absorption spectrometer, capable of analysing and determining both major and trace inorganic elements.
Working Conditions
Power requirements：220V （+5%～-10%），50/60 Hz；5000VA。
Ambient temperature：+15℃～+35℃。
Relative humidity：20～80%。
Technical Specifications
Spectral System
Grating line density: ≥1800 lines/mm.
Effective grating area: ≥50 × 50 mm².
Wavelength range: 190–900 nm.
Spectral bandwidth: Five automatically adjustable settings (0.1, 0.2, 0.4, 1.0, 2.0 nm), with automatic adjustment of slit width and energy.
Wavelength accuracy: ≤0.15 nm
Wavelength repeatability: ±0.1 nm.
*Baseline drift: Static ≤±0.002 A/30 minutes, dynamic ≤±0.005 A/30 minutes.
*Instrument spectral resolution capability: Capable of resolving the manganese doublet lines at 279.5 nm and 279.8 nm, with peak-to-valley energy between the lines ≤30% when the spectral bandwidth is 0.2 nm/mm.
Light source: Six-lamp automatic switching turret with automatic collimation.
Lamp current setting: 0–30 mA, automatically set by computer.
High-performance power supply: Built-in high-performance lamp dual-cathode power supply.
Flame Atomiser
* Characteristic concentration (Cu): 0.015 μg/mL/1%.
* Detection limit (Cu): 0.002 μg/mL.
* Precision: RSD ≤ 0.5%.
Combustion Head: Titanium combustion head, 50mm or 100mm universal combustion head.
Atomiser: Pt-Ir capillary tube, Teflon nozzle, ceramic impact ball (suitable for hydrofluoric acid).
Atomisation Chamber: Explosion-proof corrosion-resistant material atomisation chamber.
Ignition Method: Microprocessor-controlled, automatic ignition.
Gas control: Fully automated gas control system.
Regulation system: Fully automated PC-controlled flame/graphite furnace automatic switching with self-optimisation.
Safety protection: Incorporates automatic safety protection functions, including auto-flameout prevention, automatic gas line protection, acetylene leak alarm, automatic system shutdown, and automatic power cut-off upon anomalies.
Background correction: Flame: Deuterium lamp + self-absorbed background correction: Capable of correcting 1A background.
Data Processing
Measurement Methods: Flame method, hydride method.
Concentration Calculation Methods: Standard curve method (1st to 3rd order curves), automatic fitting, standard addition method.
Repeat Measurement Count: 1-99 times; calculates average value, provides standard deviation and relative standard deviation.
Result Printing: Parameter printing, data result printing, graphical printing; exportable to WORD and EXCEL documents.
Fully Chinese interface, simple and convenient operation, with software-configurable automated procedures.
*Communication Interface: USB interface for computer-to-main unit communication.
About Us
MACYLAB INSTRUMENTS INC. (hereinafter referred to as Macylab) is a high-tech enterprise possessing independent intellectual property rights. Guided by its founding philosophy ‘Technology – Transformed by You’, Macylab pursues continuous exploration and bold innovation as its corporate mission. Particularly within the analytical testing instrument sector, the company consistently develops advanced products, establishing Macylab as a premier supplier of high-quality instrumentation resources.
Macylab specialises in spectroscopic instruments including visible spectrophotometers, ultraviolet-visible spectrophotometers, atomic absorption spectrometers, ultra-micro spectrophotometers, atomic fluorescence spectrophotometers, ICP inductively coupled plasma emission spectrometers, and ICP inductively coupled plasma mass spectrometers. Currently, our products are extensively utilised across organic chemistry, inorganic chemistry, biochemistry, pharmaceuticals, environmental protection, metallurgy, petroleum, and agriculture. Leveraging extensive expertise in mechanical design, optical engineering, electrical applications, and software development, Macylab will soon introduce a new range of analytical instruments tailored to the latest market demands.
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