Determination of Copper in Water by Atomic Absorption Spectrometry

Copper is a common metallic element in natural waters and wastewaters, originating from both natural weathering processes and anthropogenic sources such as industrial discharges, mining activities, and corrosion of plumbing materials. 

Although copper is an essential micronutrient at trace levels, elevated concentrations can be toxic to aquatic life and, through drinking water, pose health risks to humans. Accurate determination of copper concentration is therefore a routine requirement in water quality monitoring, drinking water safety assessment, and industrial effluent control.

Among the various analytical techniques available, atomic absorption spectrometry (AAS) stands out as one of the most widely adopted methods for copper determination. Its popularity stems from its exceptional selectivity, high sensitivity, relatively simple operation, and the broad availability of instrumentation in routine laboratories. 

The method is standardised internationally and in China under GB/T 7475-1987 Water quality – Determination of copper, zinc, lead and cadmium – Atomic absorption spectrometry, which has been reviewed and confirmed as continuing valid as recently as March 2026. More recently, the graphite furnace variant has been updated in HJ 1453-2026, effective from May 2026.

Principles of Atomic Absorption Spectrometry

The fundamental principle of atomic absorption spectrometry is based on the absorption of characteristic electromagnetic radiation by ground-state atoms. In practice, a liquid sample is introduced into an atomisation source—typically a flame or a graphite furnace—where it is evaporated, desolvated, and dissociated into free, unexcited atoms of the target element. 

A hollow cathode lamp emitting light at a wavelength specific to copper (324.7 nm) directs a beam through the atom cloud. The ground-state copper atoms absorb a portion of this incident radiation in proportion to their concentration in the atomisation zone. The diminished light intensity is measured by a detector, and the absorbance value is compared against a calibration curve prepared from standard solutions of known copper concentration. Under the Lambert-Beer law, this absorbance is directly proportional to the concentration of copper in the original sample.

Flame Atomic Absorption Spectrometry

Flame atomic absorption spectrometry (FAAS) is the most commonly employed variant for routine copper analysis. In this technique, the sample solution is aspirated through a nebuliser into an air-acetylene flame, where atomisation occurs. For copper determination by FAAS, the method is applicable to water samples containing copper in the range of approximately 10 to 1,000 µg/L. When a 500 mL sample is concentrated into a smaller volume, the linear range typically extends from 0.05 to 2.50 mg/L, with a detection limit of approximately 0.013 mg/L.

The analytical procedure for FAAS involves several steps. The sample is collected in acid-rinsed polyethylene or glass containers. For determination of dissolved copper, the sample must be filtered through a 0.45‑µm membrane filter at the time of collection. For total recoverable copper, the unfiltered sample is acidified with nitric acid to pH < 2 for preservation. 

In the laboratory, the sample is aspirated directly into the flame, and absorbance is measured. A series of calibration standards is prepared from a copper stock solution, and a linear regression equation with a correlation coefficient exceeding 0.999 is typically achieved. Quality control measures include the analysis of reagent blanks, calibration verification standards, and spiked samples to validate accuracy.

FAAS offers the advantages of simplicity, speed, and low operational cost. However, its sensitivity is limited for trace-level analysis, and samples with copper concentrations below approximately 10 µg/L require pre-concentration or the use of more sensitive techniques.