Aplicações

Determination of Magnesium in Sodium Bicarbonate (Flame Atomic Absorption Spectrometry)

Setembro 4, 2025

1. Method Overview

After the sample is digested and atomized by flame, the absorbance is measured at a wavelength of 285.2 nm. Within a certain concentration range, the absorbance value of magnesium is proportional to its 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.	Nome	Quantidade	Technical Requirements	Acessórios
1	Flame Atomic Absorption Spectrophotometer	1 set	/	Magnesium Hollow Cathode Lamp
2	Acetylene Gas	1 cylinder	Purity ≥ 99.99%	/
3	Air Compressor	1 set	Rated discharge pressure: 0.3 MPa	/

2.1.2 Sample Pretreatment Equipment

Serial No.	Nome	Quantidade	Technical Requirements	Acessórios
1	Microwave Digestion System	1 set	/	/
2	Temperature-Controlled Hot Plate	1 set	/	/
3	Electronic Balance	1 set	Sensitivity: 0.1 mg	/
4	Ultrapure Water System	1 set	/	/
5	Micropipette	1 each	Ranges: 20 μL~200 μL, 100 μL~1000 μL	/
6	Volumetric Flask	Several	Volume: 100 mL	/
7	Colorimetric Tube	Several	Volume: 25 mL	/

2.2 Reagents

2.2.1 Raw Reagents

Serial No.	Nome	Technical Requirements	Observações
1	Nitric Acid	MOS Grade	/
2	Hydrochloric Acid	Guaranteed Reagent (GR)	/

2.2.2 Prepared Reagents

Serial No.	Nome	Preparation Method	Observações
1	Nitric Acid Solution (5+95)	Measure 50 mL of nitric acid, slowly add it to 950 mL of deionized water, and mix well.	/

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Nome	Technical Requirements	Observações
1	GBW(E)080126	Magnesium 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 0.5 g of sodium bicarbonate sample (precision to 0.001 g) into a microwave digestion vessel, add 8 mL of nitric acid, and digest the sample according to the operating procedures of the microwave digestion system. After cooling, take out the digestion vessel, and evaporate the acid on a hot plate at 140℃~160℃ until the volume is reduced to 0.5 mL~1 mL. After the digestion vessel cools down, transfer the digested solution to a 25 mL colorimetric tube. Wash the digestion vessel with a small amount of water for 2~3 times, combine the washing solutions into the colorimetric tube, dilute to the marked volume with water, and mix well for later use. Prepare a reagent blank at the same time.

Microwave Digestion Program

Step	Temperature/℃	Holding Time/min
1	100	3
2	120	3
3	140	3
4	160	3
5	180	30

3.1.2 Preparation of Standard Solutions

Preparation of Magnesium Standard Intermediate Solution (100 μg/mL): Accurately pipette 10.0 mL of the magnesium standard stock solution (1000 μg/mL) into a 100 mL volumetric flask, dilute to the marked volume with (5+95) nitric acid solution, and shake well.
Preparation of Magnesium Standard Series: Accurately pipette 0.0, 0.1, 0.2, 0.3, and 0.4 mL of the magnesium standard intermediate solution (100 μg/mL) into separate 100 mL volumetric flasks respectively. Dilute to the marked volume with (5+95) nitric acid solution and mix well. The concentrations of this standard series are 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 (Magnesium) | | — | — | | Wavelength (nm) | 285.2 | | Spectral Bandwidth (nm) | 0.2 | | Element Lamp Current (mA) | 3.0 | | Burner Height (mm) | 6 | | Fuel Gas Flow Rate (mL/min) | 1500 | | Air Compressor Pressure (MPa) | 0.22 | | Background Correction Method | None |
Sample Testing Adjust the instrument to its optimal working state, ignite the flame and adjust the fuel gas flow rate. Test the standard solutions and sample solutions in sequence, read the data, input the sample weight, and check and record the results.

3.3 Result Calculation

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

Onde:

$X$ = Magnesium content in the sample, unit: milligram per kilogram (mg/kg);
$ρ$ = Mass concentration of magnesium in the sample test solution, unit: milligram per liter (mg/L);
$ρ0$ = Mass concentration of magnesium in the blank solution, unit: milligram per liter (mg/L);
$f$ = Dilution factor of the digested sample solution;
$V$ = Total volume of the digested sample solution, unit: milliliter (mL);
$m$ = Mass of the sample, unit: gram (g).