Applications

Determination of Potassium in Sweet Potato Products (Flame Atomic Absorption Spectrometry)

September 4, 2025

1. Method Overview

After the sample is digested, it is atomized by the flame of an atomic absorption spectrometer, and the absorbance is measured at a wavelength of 766.5 nm. Within a certain concentration range, the absorbance value is proportional to the potassium content, and quantification is performed by comparison with a standard series.

2. Instruments and Reagents

2.1 Instruments and Equipment

2.1.1 Testing Instruments

Serial No.	Name	Quantity	Technical Requirements	Accessories
1	Flame Atomic Absorption Spectrophotometer	1 set	–	Potassium Hollow Cathode Lamp
2	Air Compressor	1 set	Rated discharge pressure: 0.3 MPa	–
3	Acetylene Gas	1 cylinder	Purity ≥ 99.99%	–

2.1.2 Sample Pretreatment Equipment

Serial No.	Name	Quantity	Technical Requirements	Accessories
1	Micropipette	1 each	Ranges: 100 µL~1000 µL, 1000 µL~5000 µL, 5~50 µL	–
2	Colorimetric Tube	Several	Volumes: 10 mL, 25 mL	–
3	Adjustable Hot Plate	1 set	Rated temperature: Room temperature ~ 300℃	–
4	Volumetric Flask	Several	Volumes: 100 mL, 1000 mL	–
5	Analytical Balance	1 set	Sensitivity: 0.1 mg	–
6	Erlenmeyer Flask	Several	Volume: 150 mL	–

2.2 Reagents

2.2.1 Raw Reagents

Serial No.	Name	Technical Requirements	Remarks
1	Nitric Acid	MOS Grade	–

2.2.2 Prepared Reagents

Serial No.	Name	Preparation Method	Remarks
1	Nitric Acid Solution (5+95)	Measure 50 mL of nitric acid and mix uniformly with 950 mL of water.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Name	Technical Requirements	Remarks
1	GBW(E)080125	Potassium Single-Element Standard Solution	Concentration: 1000 μg/mL	National Institute of Metrology, China

3. Operation Procedure

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Accurately weigh 1~2 g of the sample (precision to 0.001 g) into an Erlenmeyer flask, add 10 mL of nitric acid, and digest on a hot plate (reference conditions: 80℃/1 h, 120℃/1 h, 140℃/2 h, 160℃/2 h, then raise the temperature to 180℃). If the solution turns brown, add more nitric acid and continue digestion until white fumes are emitted. When the solution becomes colorless and transparent or slightly yellow, cool it down and dilute to the mark in a 10 mL colorimetric tube with water. Prepare a reagent blank at the same time.

3.1.2 Preparation of Standard Solutions

Preparation of Potassium Standard Intermediate Solution (10 μg/mL):
Accurately pipette 1 mL of the potassium national standard solution into a 100 mL volumetric flask, add nitric acid solution (5+99) to the mark, and the standard intermediate solution (10 μg/mL) is obtained.
Preparation of Potassium Standard Series:
Accurately pipette 0.0, 1.0, 2.0, 3.0, and 4.0 mL of the potassium standard intermediate solution (10 μg/mL) into separate 100 mL volumetric flasks respectively. Add nitric acid solution (5+95) to the mark to obtain the potassium standard series with concentrations of 0.0, 0.1, 0.2, 0.3, and 0.4 μg/mL.

3.2 Sample Testing

Testing Conditions Reference testing conditions for the flame atomic absorption spectrophotometer: | Parameter | Specification | | Wavelength | 766.5 nm | | Spectral Bandwidth | 0.2 nm | | Element Lamp Current | 2.0 mA | | Burner Height | 5 mm | | Fuel Gas Flow Rate | 1500 mL/min | | Air Compressor Pressure | 0.22 MPa |
Sample Testing Introduce the potassium standard series solutions into the flame atomizer in ascending order of concentration, and measure the absorbance values. Plot a standard curve with the mass concentration of potassium in the standard series solutions as the abscissa and the corresponding absorbance values as the ordinate.

Under the same experimental conditions as those for determining the standard solutions, introduce the blank solution and the sample test solution into the atomizer respectively, measure their corresponding absorbance values, and perform quantification by comparison with the standard series.

3.3 Result Calculation

The potassium content in the sample is calculated using the following formula:

Where:

$X$ = Potassium content in the sample, unit: milligram per kilogram (mg/kg);
$\rho$ = Mass concentration of potassium in the sample test solution, unit: microgram per milliliter (μg/mL);
$\rho_{0}$ = Mass concentration of potassium in the blank solution, unit: microgram per milliliter (μg/mL);
$V$ = Volume of the digested sample solution after constant volume, unit: milliliter (mL);
$f$ = Dilution factor of the digested sample solution;
$m$ = Mass of the sample, unit: gram (g).