Applications

Determination of Cadmium in Surface Water (Graphite Furnace Atomic Absorption Spectrometry)

September 4, 2025

1. Method Overview

After appropriate treatment, the sample is injected into a graphite tube atomizer. The cadmium ions contained in the sample are evaporated and dissociated into atomic vapor at high atomization temperature in the graphite tube. The ground-state atoms of the element to be determined absorb the resonance line emitted by the cadmium hollow cathode lamp. Within a certain range, the absorption intensity is proportional to the concentration.

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 Spectrometer	1 set	–	Cadmium Hollow Cathode Lamp
2	Cooling Circulating Water System	1 set	Rated flow rate of water pump: 3.5 L/min	–
3	Argon Gas	1 cylinder	Purity ≥ 99.99%	–

2.1.2 Sample Pretreatment Equipment

Serial No.	Name	Quantity	Technical Requirements	Accessories
1	Temperature-Controlled Hot Plate	1 set	Room temperature ~ 300℃	–
2	Colorimetric Tube	Several	Volume: 10 mL	–
3	Micropipette	1 each	Ranges: 20 μL~200 μL, 1000 μL~5000 μL	–
4	Volumetric Flask	Several	Volumes: 100 mL, 1000 mL	–

2.2 Reagents

2.2.1 Raw Reagents

Serial No.	Name	Technical Requirements	Remarks
1	Nitric Acid	–	–

2.2.2 Prepared Reagents

Serial No.	Name	Preparation Method	Remarks
1	Nitric Acid Solution (1+99)	Measure 10 mL of nitric acid, add it to a 1000 mL volumetric flask containing a small amount of water, and dilute to the marked volume with water.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Name	Technical Requirements	Remarks
1	GSB G 62040-90	Cadmium Standard Solution	Concentration: 1000 mg/L	Central Iron and Steel Research Institute

3. Operation Procedure

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Clear water samples can be directly determined. For water samples with high suspended solids, acidification and digestion of organic substances are required before analysis.

3.1.2 Preparation of Standard Solutions

Preparation of Cadmium Standard Intermediate Solution (50 μg/mL): Accurately pipette 5.0 mL of the cadmium 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 Cadmium Standard Intermediate Solution (1.0 μg/mL): Accurately pipette 2.0 mL of the cadmium standard intermediate solution (50 μg/mL) into a 100 mL volumetric flask, dilute to the marked volume with (1+99) nitric acid solution, and shake well.
Preparation of Cadmium Standard Working Solution (100 ng/mL): Accurately pipette 10.0 mL of the cadmium standard solution (1.0 μg/mL) into a 100 mL volumetric flask, dilute to the marked volume with (1+99) nitric acid solution, and shake well.
Preparation of Cadmium Standard Series: Pipette 0.0 mL, 0.50 mL, 1.00 mL, 3.00 mL, 5.00 mL, and 7.00 mL of the cadmium standard working solution into separate 100 mL volumetric flasks respectively. Dilute to the marked volume with (1+99) nitric acid solution and shake well. This results in a standard series with cadmium concentrations of 0.00 ng/mL, 0.5 ng/mL, 1.00 ng/mL, 3.00 ng/mL, 5.00 ng/mL, and 7.00 ng/mL.

3.2 Sample Testing

Testing Conditions Reference testing conditions for the atomic absorption spectrophotometer: | Parameter | Specification | | — | — | | Wavelength (nm) | 228.8 | | Spectral Bandwidth (nm) | 0.4 | | Element Lamp Current (mA) | 2.0 | | Background Correction Method | Deuterium Lamp Background Correction | | Injection Volume (μL) | 15 |

Graphite Furnace Heating Program

Step	Temperature (℃)	Heating Time (S)	Holding Time (S)	Internal Gas Flow
1	110	10	10	High
2	350	10	10	High
3	1700	0	3	Off
4	1900	1	2	High

Sample Testing Sequentially pipette the reagent blank, standard series, and sample solution, inject them into the graphite tube, and determine their absorbance. Subtract the absorbance of the zero-standard solution from the absorbance of each standard solution. Plot a working curve with concentration as the abscissa and the corresponding absorbance as the ordinate. Based on the measured absorbance of the test solution, find the mass concentration of cadmium from the working curve.

3.3 Result Calculation

The concentration of cadmium in the water sample is calculated using the following formula:

Where:

$ρ(Cd)$ = Mass concentration of cadmium in the water sample, unit: microgram per liter (μg/L);
$ρ1$ = Concentration of cadmium in the sample obtained from the calibration curve, unit: microgram per liter (μg/L);
$V1$ = Volume of the sample used for determination, unit: milliliter (mL);
$V$ = Volume of the water sample taken, unit: milliliter (mL).