Determination of Copper Content in Copper Alloys by Flame Atomic Absorption Spectroscopy

Introduction:

Copper alloys find extensive application across industrial sectors, particularly in the current high-speed rail construction where they are extensively utilised for circuit line construction. Consequently, the requirements for copper alloy usage within circuit power systems are of paramount importance. Testing and inspection of copper alloy materials are subject to stringent protocols. However, existing methods for determining copper content in copper alloys are cumbersome and complex. Consequently, this study proposes a simplified standard curve method that avoids interference from the copper matrix while accurately quantifying copper content in copper alloys.

    This paper introduces a sample analysis method employing flame atomic absorption spectroscopy to directly measure copper in copper alloys using the 249.2nm absorption line of copper. The results obtained from this method were found to be identical to those from the 324.8nm standard addition method. This establishes a simplified testing method for determining copper content in copper alloys, enhancing analytical accuracy while streamlining the testing process.

1 Experimental Section

1.1 Apparatus and Equipment

AA1800 atomic absorption spectrophotometer

Adjustable hotplate. Ultrapure water system. Cu hollow cathode lamp.

1.2 Reagents and Solutions

 (1) Nitric acid, analytical grade, 68–70%.

 (2) High-purity deionised water. Resistivity ≥ 18 MΩ·cm.

 (3) Copper standard solution (concentration 1000 μg/ml).

1.3 Sample Preparation and Testing

1) Sample Preparation: Accurately weigh 0.1106g of copper alloy sample and place it in a 100ml beaker. Add 5ml of concentrated nitric acid and heat gently on an electric hotplate. To prevent vigorous reaction, add a small amount of deionised water. Heat until all nitric acid fumes have dissipated, then remove and allow to cool to room temperature. Once cooled, transfer the sample to a 50ml volumetric flask for subsequent testing.

2) Standard Curve:

(1) Standard Curve Method: Prepare the curve by accurately measuring 200 μl, 400 μl, and 800 μl of 1000 μg/ml copper standard solution into three separate 10 ml volumetric flasks. Add 0.5 ml concentrated nitric acid to each, then dilute to volume with deionised water. The resulting concentrations are 20, 40, and 80 μg/ml respectively. Directly determine the standard curve and measure the sample solution 1.

(2) Standard Addition Method Preparation: Transfer 1.0 ml from Sample Solution 2 into four 10 ml volumetric flasks. Flask 1 is diluted to volume with deionised water. Flasks 2, 3, and 4 are each spiked with 25, 50, and 75 µl of the 1000 µg/ml copper standard solution, yielding concentrations of 0, 0.5, 1.0, and 1.5 µg/ml respectively. The standard addition method is employed for determination.

Sample Solution 1: Dilute the volumetrically adjusted sample solution 1000-fold.

Sample Solution 2: Dilute the volumetrically adjusted sample solution 50-fold.

3) Instrument Conditions:

(1) Standard Curve Method: Lamp current: 3mA, High voltage: 400V, Spectral bandwidth: 249.2nm.

              Acetylene flow rate: 2.0L/min.

(2) Standard Addition Method: Lamp current: 3mA; High voltage: 409V; Spectral bandwidth: 324.9nm.

              Acetylene flow rate: 2.0L/min.

4) Analysis Results:

By comparing the outcomes of both methods through testing, it is evident that employing the secondary sensitivity line of copper at 249.2 nm and directly applying the standard curve method effectively mitigates significant test result deviations caused by matrix interference. This approach reduces interference factors affecting copper in the sample by lowering the test sensitivity. The method is convenient, rapid, easy to operate, and highly accurate.