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Determination of Lead in Olive Oil (Graphite Furnace Atomic Absorption Spectrometry)

Tháng 9 4, 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, the sample absorbs the resonance line at 283.3 nm. Within a certain concentration range, the absorbance value is proportional to the lead 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.	Tên	Số lượng	Technical Requirements	Phụ kiện
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.	Tên	Số lượng	Technical Requirements	Phụ kiện
1	Microwave Digestion System	1 set	Equipped with platinum resistor 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.	Tên	Technical Requirements	Nhận xét
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.	Tên	Preparation Method	Nhận xét
1	Nitric Acid Solution (1+99)	Measure 10 mL of nitric acid, slowly add it to 990 mL of water, and mix well.	–
2	Nitric Acid Solution (5+95)	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 nitric acid solution (1+9), then add 2 g of ammonium dihydrogen phosphate. After dissolution, dilute to 100 mL with nitric acid solution (5+95) and mix well.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Tên	Technical Requirements	Nhận xét
1	GBW 08619	Lead 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 0.2 g of the solid sample (precision to 0.001 g) into a microwave digestion vessel, add 5 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 approximately 1 mL. After the digestion vessel cools down, transfer the digested solution to a 25 mL volumetric flask with deionized water. Wash the digestion vessel with a small amount of water for 2~3 times, combine the washing solutions into the volumetric flask, and dilute to the marked volume with water. Mix well for later use; this is the sample test solution. Prepare a reagent blank test at the same time.

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: For the lead standard solution (1.0 μg/mL), accurately pipette 0.1 mL of the lead standard stock solution (1000 μg/mL) into a 100 mL volumetric flask, dilute to the marked volume with (1+99) nitric acid solution, and shake well.
Preparation of Lead Standard Series: Accurately pipette 0.0, 0.1, 0.2, 0.3, and 0.4 mL of the lead standard 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 the lead standard series solutions with concentrations of 0.0, 10.0, 20.0, 30.0, and 40.0 ng/mL.

3.2 Sample Testing

Testing Conditions Reference testing conditions for the graphite furnace atomic absorption spectrophotometer: | Parameter | Specification (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	Thủ tục	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

Sample Testing In ascending order of mass concentration, inject 10 μL of the lead standard series solution and 5 μL of the diammonium hydrogen phosphate-palladium nitrate solution into the graphite furnace simultaneously. After atomization, measure the absorbance values. Plot a standard curve with mass concentration as the abscissa and absorbance value as the ordinate. Read the data, input the sample weight, and check and record the results.

3.3 Result Calculation

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

Ở đâu:

$X$ = Lead content in the sample, unit: milligram per kilogram (mg/kg);
$C1$ = Mass concentration of lead in the sample test solution, unit: nanogram per milliliter (ng/mL);
$C2$ = Mass concentration of lead in the blank solution, unit: nanogram per milliliter (ng/mL);
$V$ = Volume of the sample after constant volume, unit: milliliter (mL);
$m$ = Mass of the sample, unit: gram (g);
1000 = Conversion factor.