Applications

Determination of Lead in Graphite Powder (Graphite Furnace Atomic Absorption Spectrometry)

October 10, 2025

1. Method Overview

After the sample is digested by microwave, it is injected into the graphite furnace of an atomic absorption spectrophotometer. After electrothermal atomization, it absorbs the resonance line at 283.3 nm. Within a certain concentration range, the absorbance is proportional to the lead content. Quantitative determination 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	Graphite Furnace Atomic Absorption Spectrophotometer	1 set	–	Lead Hollow Cathode Lamp
2	Argon Gas	1 cylinder	Purity ≥ 99.99%	–
3	Cooling Circulating Water System	1 set	Rated water pump flow rate: 3.5 L/min	–

2.1.2 Sample Pretreatment Equipment

Serial No.	Name	Quantity	Technical Requirements	Accessories
1	Microwave Digestion System	1 set	Equipped with platinum resistance and infrared temperature measurement; pressure measurement accuracy: ±0.1 ℃	–
2	Temperature-Controlled Hot Plate	1 set	Rated temperature range: Room temperature ~ 300 ℃	–
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	Test Tube	Several	Volume: 25 mL	–

2.2 Reagents

2.2.1 Raw Reagents

Serial No.	Name	Technical Requirements	Remarks
1	Hydrochloric Acid	Guaranteed Reagent (GR)	–
2	Nitric Acid	MOS Grade	–

2.2.2 Prepared Reagents

Serial No.	Name	Preparation Method	Remarks
1	(1+99) Nitric Acid Solution	Measure 10 mL of nitric acid, slowly add it to 990 mL of water, and mix well.	–
2	(5+95) Nitric Acid Solution	Measure 5 mL of nitric acid, slowly add it to 95 mL of water, and mix well.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Name	Technical Requirements	Remarks
1	GSB G 62071-90	Lead Single-Element Standard Solution	Concentration: 1000 μg/mL	Provided by National Analysis and Testing Center for Nonferrous Metals and Electronic Materials

3. Operational Procedures

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Weigh 0.25 g of the sample (accurate to 0.00001 g) into a digestion tank. Add 3 mL of concentrated nitric acid and 9 mL of concentrated hydrochloric acid, cover and tighten the digestion tank, then place it in the microwave digestion system for digestion. Prepare a blank sample using the same method. After cooling, filter the solution and dilute it to the marked volume in a 25 mL volumetric flask. The solution is ready for on-machine testing.

Microwave Heating 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 Lead Standard Intermediate Solution

Lead standard intermediate solution (1.0 μg/mL): Accurately pipette 0.1 mL of the lead standard solution (1000 μg/mL) into a 100 mL volumetric flask, dilute to the marked volume with (5+95) nitric acid solution, and mix well.
Preparation of Lead Standard Series

Accurately pipette 0.0, 0.5, 1.0, 1.5, 2.0, and 3.0 mL of the lead standard intermediate solution (1.0 μg/mL) into separate 100 mL volumetric flasks respectively. Dilute each to the marked volume with (1+99) nitric acid solution to obtain lead standard series solutions with concentrations of 0.0, 5.0, 10.0, 15.0, 20.0, and 30.0 ng/mL.

3.2 Sample Testing

Testing Conditions

Reference Conditions for Graphite Furnace Atomic Absorption Spectrophotometer

Element	Lead
Wavelength (nm)	283.3
Spectral Bandwidth (nm)	0.4
Element Lamp Current (mA)	2
Background Correction Method	Deuterium Lamp

Graphite Furnace Heating Program

Step	Procedure	Temperature (℃)	Heating Time (s)	Holding Time (s)
1	Drying	120	10	10
2	Ashing	650	10	10
3	Atomization	1900	0	2
4	Cleaning	2000	1	2

Sample Testing

Inject 10 μL of each lead standard series solution into the graphite furnace in ascending order of mass concentration. After atomization, measure the absorbance. Plot a standard curve with mass concentration as the abscissa and absorbance as the ordinate. Input the sample weight, then read and record the test results.