Applications

1. Method Overview

After sample treatment, it is introduced into an atomic absorption spectrometer, atomized, and the absorbance is measured. Within a certain concentration range, the absorbance value is proportional to the lead content, and quantitative analysis is performed by comparison with the standard series.

2. 2. Instruments and Reagents

2.1 Instruments and Equipment

2.1.1 Testing Instruments

Graphite Furnace Atomic Absorption Spectrophotometer (With Lead hollow cathode lamp)

Cooling Circulating Water System (Pump rated flow: 3.5 L/min)

Argon Gas (Purity≥99.99%)

2.1.2 Pretreatment Equipment

Electronic Balance (Sensitivity: 0.1 mg)

Conical Flask  (50 mL)

Glass Watch Glass (70 mm)

Glass Funnel  (75 mm)

Slow Quantitative Filter Paper (9 cm)

Adjustable Electric Hot Plate (Rated temperature: room temperature~300℃

Micropipett (20μL~200μL,100μL~1000μL,1000μL~5000μL)

Volumetric Flask (100 mL, 1000 mL)

Colorimetric Tube

2.2 Reagents

2.2.1 Reagents

Nitric Acid (MOS grade)

Hydrochloric Acid (Ultra-pure grade)

3. Operation Procedure

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

1)Sample Pretreatment

Weigh 0.25 g of the sample into a 50 mL conical flask, moisten with 2 mL of water, add 4.5 mL of hydrochloric acid and 1.5 mL of nitric acid. Cover the flask, place it on an electric hot plate, heat to a gentle boil, and maintain for 2 hours. Cool to room temperature. Place a slow quantitative filter paper in a glass funnel, rinse the filter paper with 20 mL of nitric acid solution (1+99), and discard the filtrate. Transfer the digestion solution to the filter paper for filtration. Wash the conical flask 2–3 times with a small amount of nitric acid solution (1+99), transfer the washings to the filter paper, filter, and dilute to a 25mL colorimetric tube with water, then mix well. Perform a blank test alongside the sample.

2)Preparation of Lead Element Test Solution

Accurately transfer 1.0 mL of the sample solution to a 10 mL colorimetric tube, dilute to the mark with nitric acid solution (1+99), and shake well. Meanwhile, conduct a blank test: the blank test solution shall contain the same types and amounts of reagents as the test solution, except for the sample.

3.1.2 Preparation of Standard Solutions

1)Preparation of Lead Standard Intermediate Solution

Lead standard intermediate solution (1.0μg/mL): Accurately transfer 0.100 mL of lead standard solution (1000μg/mL) to a 100 mL volumetric flask, add 1 mL of nitric acid, dilute to the mark with deionized water, and mix well.

2)Preparation of Lead Standard Series

Transfer 0 mL, 0.5 mL, 1.0 mL, 2.0 mL, and 3.0 mL of the lead standard intermediate solution (1.0μg/mL) into 100 mL volumetric flasks, add 1 mL of nitric acid to each, dilute to the mark with deionized water, and mix well. The concentrations of this series are: 0 ng/mL, 5 ng/mL, 10 ng/mL, 20 ng/mL, 30 ng/mL.

3.2 Sample Testing Procedure

Measure the absorbance of the standard solutions, blank test solution, and test solution in sequence.

Subtract the absorbance of the zero standard solution from the absorbance of each standard solution. Take the mass concentration as the abscissa and the corresponding absorbance as the ordinate to plot the working curve. According to the measured absorbance of the test solution, obtain the lead mass concentration from the working curve.

3.3 Result Calculation

The lead content in the sample, expressed as mass fraction X (in mg/kg), is calculated by the formula:

Where:

c= Lead content in the test solution, in ng/mL;

c0= Lead content in the blank solution, in ng/mL;

V= Total volume of the sample digestion solution, in mL;

f = Dilution factor;

m = Sample mass, in g;

1000 = Conversion coefficient.