Applications

Determination of Lead in Olive Oil (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	Circulating Cooling Water System	1 set	–	–

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	–	–
3	Electronic Balance	1 set	Sensitivity: 0.1 mg	–
4	Ultrapure Water System	1 set	–	–
5	Volumetric Flask	Several	Volume: 100 mL	–
6	Test Tube	Several	Volume: 10 mL	–

2.2 Reagents

2.2.1 Raw Reagents

Serial No.	Name	Technical Requirements	Remarks
1	Diammonium Hydrogen Phosphate	Analytical Reagent (AR)	–
2	Hydrochloric Acid	Guaranteed Reagent (GR)	–
3	Nitric Acid	MOS Grade	–
4	Palladium Nitrate	Analytical Reagent (AR)	–

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.	–
3	Diammonium Hydrogen Phosphate – Palladium Nitrate Solution	Weigh 0.02 g of palladium nitrate, dissolve it with a small amount of (1+9) nitric acid solution. Then add 2 g of diammonium hydrogen phosphate, and after dissolution, dilute to 100 mL with (5+95) nitric acid solution. Mix well.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Name	Technical Requirements	Remarks
1	GBW 08619	Lead Single-Element Standard Substance Solution	Concentration: 1000 μg/mL	Provided by National Institute of Metrology, China

3. Operational Procedures

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Accurately weigh 0.2 g of the solid sample (accurate to 0.001 g) into a microwave digestion tank, add 5 mL of nitric acid, and digest the sample according to the microwave digestion operation steps. After cooling, take out the digestion tank and evaporate the acid on a hot plate at 140℃~160℃ until the volume is about 1 mL. After the digestion tank cools down, transfer the digestion solution to a 25 mL volumetric flask with deionized water. Wash the digestion tank 2~3 times with a small amount of water, combine the washing solutions into the volumetric flask, and dilute to the marked volume with water. Mix well for use; this is the sample test solution. Conduct a reagent blank test simultaneously.

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 (1+99) nitric acid solution, and mix well.
Preparation of Lead Standard Series

Accurately pipette 0.0, 0.1, 0.2, 0.3, and 0.4 mL of the lead standard intermediate solution (1.0 μg/mL) into separate 10 mL volumetric flasks respectively. Dilute to the marked volume with (1+99) nitric acid solution to obtain lead standard series solutions with concentrations of 0.0, 10.0, 20.0, 30.0, and 40.0 ng/mL.

3.2 Sample Testing

1) 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	15
3	Atomization	1900	0	2
4	Cleaning	2000	1	2

2) Sample Testing

Inject 10 μL of each lead standard series solution and 5 μL of the diammonium hydrogen phosphate – palladium nitrate solution into the graphite furnace simultaneously 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 results.