Applications

Determination of Lead in Food Additive Sodium Pyrophosphate (Flame Atomic Absorption Spectrometry)

septembre 4, 2025

1. Method Overview

After the sample is treated, lead ions form a complex with sodium diethyldithiocarbamate (DDTC) under a certain pH condition. The complex is extracted and separated with 4-methyl-2-pentanone (MIBK), then introduced into an atomic absorption spectrometer. After flame atomization, the absorbance is measured at a wavelength of 283.3 nm. Within a certain concentration range, the absorbance value of lead 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.	Nom	Quantité	Technical Requirements	Accessoires
1	Flame Atomic Absorption Spectrophotometer	1 set	–	Lead 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.	Nom	Quantité	Technical Requirements	Accessoires
1	Electronic Balance	1 set	Sensitivity: 0.1 mg	–
2	Beaker	Several	Volume: 150 mL	–
3	Adjustable Hot Plate	1 set	Temperature range: Room temperature ~ 300℃	–
4	Separatory Funnel	Several	Volume: 250 mL	–
5	Micropipette	1 each	Ranges: 100 μL~1000 μL, 1000 μL~5000 μL	–
6	Colorimetric Tube	Several	Volume: 10 mL	–

2.2 Reagents

2.2.1 Raw Reagents

Serial No.	Nom	Technical Requirements	Remarques
1	4-Methyl-2-pentanone (MIBK)	Analytical Reagent (AR)	–
2	Ammonia Water	Analytical Reagent (AR)	–
3	Ammonium Sulfate	Guaranteed Reagent (GR)	–
4	Ammonium Citrate	Analytical Reagent (AR)	–
5	Sodium Diethyldithiocarbamate (DDTC)	Guaranteed Reagent (GR)	–
6	Bromothymol Blue	Analytical Reagent (AR)	–
7	Nitric Acid	MOS Grade	–

2.2.2 Prepared Reagents

Serial No.	Nom	Preparation Method	Remarques
1	Ammonia Water Solution (1+1)	Measure 50 mL of ammonia water, add it to 50 mL of water, and mix well.	–
2	Ammonium Sulfate Solution (300 g/L)	Weigh 30 g of ammonium sulfate, dissolve it in water, and dilute to 100 mL with water.	–
3	Ammonium Citrate Solution (250 g/L)	Weigh 25 g of ammonium citrate, dissolve it in water, and dilute to 100 mL with water.	–
4	Sodium Diethyldithiocarbamate (DDTC) Solution (50 g/L)	Weigh 5 g of sodium diethyldithiocarbamate, dissolve it in water, and dilute to 100 mL with water.	–
5	Bromothymol Blue Indicator Solution (1 g/L)	Weigh 0.1 g of bromothymol blue, dissolve it in water, and dilute to 100 mL with water, then mix well.	–
6	Nitric Acid Solution (5+95)	Measure 50 mL of nitric acid, add it to 950 mL of water, and mix well.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Nom	Technical Requirements	Remarques
1	GSB G 62071-90	Lead Standard Solution	Concentration: 1000 μg/mL	Central Iron and Steel Research Institute, National Iron and Steel Materials Testing Center

3. Result Calculation

The lead content is expressed as the mass fraction

W

of lead (Pb), in units of mg/kg, calculated by the following formula:

Où:

$m1$ = Mass of lead in the test solution obtained from the working curve, unit: milligram (mg);
$m0$ = Mass of lead in the blank test solution obtained from the working curve, unit: milligram (mg);
$m$ = Mass of the sample, unit: gram (g).

The arithmetic mean of the parallel determination results is taken as the final determination result. The absolute difference between the two parallel determination results shall not exceed 1 mg/kg.