Applications

Determination of Cadmium in Nettle Leaves (Hydride Generation Atomic Fluorescence Spectrometry)

July 28, 2025

1. Method Overview

After microwave digestion of the sample, atomic fluorescence is generated under excitation by a high-intensity cadmium hollow cathode lamp. The fluorescence intensity is proportional to the concentration of cadmium in the test solution under fixed conditions, 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.	Name	Quantity	Technical Requirements	Accessories
1	Atomic fluorescence spectrometer	1 set		Cadmium hollow cathode lamp
2	Argon gas	1 cylinder	Purity ≥ 99.999%

2.1.2 Pretreatment Equipment

Serial No.	Name	Quantity	Technical Requirements	Accessories
1	Electronic balance	1 set	Sensitivity: 1 mg
2	Microwave digestion system	1 set		PTFE digestion inner tank, digestion and acid-removal device
3	Adjustable electric hot plate	1 set	/
4	Micropipette	1 each	100 μL~1000 μL; 1000 μL~5000 μL
5	Colorimetric tube	Several	10 mL
6	Volumetric flask	Several	100 mL

2.2 Reagents

2.2.1 Reagents

Serial No.	Name	Technical Requirements
1	Nitric acid	Guaranteed reagent
2	Hydrochloric acid	Guaranteed reagent
3	Thiourea	Analytical reagent
4	Potassium hydroxide	Analytical reagent
5	Potassium borohydride	Analytical reagent

2.2.2 Prepared Reagents

Serial No.	Name	Preparation Method
1	Hydrochloric acid solution (1+99)	Measure 1 mL of hydrochloric acid into a 100 mL volumetric flask containing a small amount of water, then add water to the mark.
2	Carrier solution (1% thiourea + 0.5% hydrochloric acid + 0.1% cobalt standard solution)	Weigh 10 g of thiourea into a 1000 mL volumetric flask containing a small amount of water. After dissolution, add 5 mL of hydrochloric acid and 1 mL of 1000 μg/mL cobalt standard solution, then dilute to the mark with deionized water.
3	Reducing agent (1% potassium hydroxide + 1.5% potassium borohydride)

2.3 Reference Standards

2.3.1 Stock Solutions

Serial No.	No.	Name	Technical Requirements	Remarks
1	GBW08619	Cadmium single-element solution standard substance	1000 μg/mL	National Institute of Metrology, China

3. Operational Procedures

3.1 Preparation of Test Solution

Weigh 0.5 g of the sample into a digestion tube, add 8 mL of nitric acid, shake to mix evenly, and digest in a microwave digestion instrument. The recommended microwave digestion conditions are shown in the table below (digestion conditions can be adjusted according to different instruments). After digestion, cool the tube, place it in a digestion and acid-removal device, and heat at 140°C until completely dry. Add a small amount of water and continue heating to dryness (repeat three times). Remove and cool, add 0.1 mL of hydrochloric acid, transfer to a 10 mL colorimetric tube with deionized water, dilute to the mark, and mix well for testing. Perform a reagent blank test simultaneously.

Microwave Digestion Heating Program

Step	Temperature (℃)	Holding Time (min)
1	80	3
2	120	5
3	140	5
4	160	5
5	180	30

3.2 Preparation of Standard Solutions

Preparation of cadmium standard intermediate solution (1 μg/mL): Accurately pipette 0.10 mL of cadmium standard stock solution (1000 μg/mL) into a 100 mL volumetric flask, dilute to the mark with (1+99) hydrochloric acid solution, and shake well.
Preparation of cadmium standard working solution (1 ng/mL): Accurately pipette 0.1 mL of cadmium standard intermediate solution (1 μg/mL) into a 100 mL volumetric flask, dilute to the mark with (1+99) hydrochloric acid solution, and shake well.
Preparation of cadmium standard series: The instrument automatically dilutes to prepare a standard series with concentrations of 0.00 ng/mL, 0.10 ng/mL, 0.20 ng/mL, 0.40 ng/mL, 0.80 ng/mL, and 1.00 ng/mL.

3.3 Sample Testing

Testing Conditions Reference Conditions for Atomic Fluorescence Spectrometer

Parameter	Value
Negative high voltage (V)	280
Lamp current (mA)	40/40
Atomization temperature (℃)	200
Carrier gas flow rate (mL/min)	300
Shielding gas flow rate (mL/min)	600
Measurement method	Standard curve method
Reading mode	Peak area
Delay time (s)	2.0
Reading time (s)	20
Sample injection volume (mL)	1.0

Sample Testing Adjust the instrument to the optimal state. Use the mixed solution of 1% thiourea + 0.5% hydrochloric acid + 0.1% cobalt standard solution as the carrier solution, and the mixed solution of 1% potassium hydroxide + 1.5% potassium borohydride as the reducing agent. After the carrier blank discriminant value is less than 10, inject the cadmium standard working solution to determine its fluorescence intensity. Plot a standard curve with mass concentration as the abscissa and fluorescence intensity as the ordinate.

Under the same experimental conditions as the standard series, introduce the blank solution and sample solution into the instrument respectively, determine their fluorescence intensities, and quantify by comparison with the standard series.