Applications

Determination of Chromium in Refined Sulfur (Graphite Furnace Atomic Absorption Spectrometry)

October 10, 2025

1. Method Overview

After the sample is digested, its absorbance is measured at a wavelength of 357.9 nm via graphite furnace atomization. Within a certain concentration range, the absorbance of chromium is proportional to its content. Quantitative determination is conducted by comparing 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	Graphite Furnace Atomic Absorption Spectrophotometer	1 set	–	Chromium Hollow Cathode Lamp
2	Circulating Water System	1 set	–	–
3	Argon Gas	1 cylinder	Purity ≥ 99.99%	–

2.1.2 Sample Pretreatment Equipment

Serial No.	Name	Quantity	Technical Requirements	Accessories
1	Porcelain Crucible	Several	Volume: 100 mL	–
2	Electric Furnace	1 set	–	–
3	Micropipette	1 each	Ranges: 100 μL ~ 1000 μL, 1000 μL ~ 5000 μL	Tips: 1 mL, 5 mL

2.2 Reagents

2.2.1 Raw Reagents

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

2.2.2 Prepared Reagents

Serial No.	Name	Preparation Method	Remarks
1	Nitric Acid Solution (1+99)	Measure 1 mL of nitric acid, add it to 99 mL of water, and mix well.	–

2.3 Reference Standards

2.3.1 Stock Solution

Serial No.	No.	Name	Technical Requirements	Remarks
1	GSB 04-1740-2004	National Liquid Standard Sample – Chromium	Concentration: 1000 μg/mL	Provided by National Analysis and Testing Center for Nonferrous Metals and Electronic Materials

3. Operational Procedures

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Weigh 5 g of the sample (accurate to 0.1 g) and place it in a 100 mL porcelain crucible. Heat the crucible on an electric furnace until the sample burns. Move the crucible to a fume hood and wait until the sulfur is completely burned out. Then, heat it on the electric furnace for another 5 minutes. Remove the crucible and let it cool. Add 5 mL of nitric acid and 15 mL of water, then heat until the residue is completely dissolved. After cooling, transfer the solution to a 25 mL colorimetric tube, dilute to the marked volume with water, and mix well.

3.1.2 Preparation of Standard Solutions

Preparation of Chromium Standard Intermediate Solution

Accurately pipette 100 μL of the national chromium standard solution into a 100 mL volumetric flask. Dilute to the marked volume with (1+99) nitric acid solution to obtain a chromium standard intermediate solution with a concentration of 1 μg/mL.
Preparation of Chromium Standard Series

Pipette 0.0, 0.25, 0.5, 1.0, and 2.0 mL of the chromium standard intermediate solution (1 μg/mL) into separate 100 mL volumetric flasks respectively. Add (1+99) nitric acid solution to the marked volume to obtain a chromium standard series with concentrations of 0.0, 2.5, 5.0, 10.0, and 20.0 ng/mL.

3.2 Sample Testing

(1) Testing Conditions

Reference Conditions for Graphite Furnace Atomic Absorption Spectrophotometer

Parameter	Specification
Element	Chromium (Cr)
Wavelength (nm)	357.9
Spectral Bandwidth (nm)	0.4
Element Lamp Current (mA)	2.0
Filter Coefficient	0.1
Integration Time (s)	2

Graphite Furnace Heating Program

Element	Drying Temperature (℃)	Drying Time (s)	Ashing Temperature (℃)	Ashing Time (s)	Atomization Temperature (℃)	Atomization Time (s)	Cleaning Temperature (℃)	Cleaning Time (s)
Cr	110	20	600	20	2300	3	2400	2

(2) Sample Testing

Open the argon cylinder and adjust the argon pressure gauge to 0.5 MPa. Set the instrument to its optimal working state, and measure the absorbance of the reagent blank, standard series, and sample solution at a wavelength of 357.9 nm.

Subtract the absorbance of the zero-standard solution from the absorbance of each standard solution. Plot a working curve with the mass concentration of chromium (μg/L) as the abscissa and the corresponding absorbance as the ordinate. Based on the measured absorbance of the test solution and the blank test solution, find the mass of chromium from the working curve.