One method to measure copper in soil involves extracting it using a DTPA solution followed by analysis.
Here's a breakdown of a common method for measuring copper concentration in soil:
1. DTPA Extraction:
- Procedure: A known weight of air-dried soil (e.g., 10 grams) is combined with a specific volume of DTPA (Diethylenetriaminepentaacetic acid) extracting solution (e.g., 20 milliliters).
- Purpose: DTPA acts as a chelating agent, binding to the copper ions in the soil and making them soluble in the solution. This extracts the copper from the soil matrix.
- Shaking: The mixture is shaken for a specified duration (e.g., two hours) to ensure adequate extraction.
2. Separation and Filtration:
* **Separation:** After shaking, the mixture is allowed to settle or is centrifuged to separate the solid soil particles from the liquid extract.
* **Filtration:** The liquid extract is then filtered to remove any remaining fine particles, ensuring a clear solution for analysis.3. Analysis (Determination of Copper Concentration):
Several analytical techniques can be used to determine the copper concentration in the DTPA extract. Common methods include:
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Atomic Absorption Spectrophotometry (AAS): This technique measures the absorption of light by free copper atoms in a flame. The amount of light absorbed is proportional to the copper concentration in the sample.
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Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES): This method introduces the sample into an inductively coupled plasma, which excites the copper atoms. When the atoms return to their ground state, they emit light at specific wavelengths. The intensity of the emitted light is proportional to the copper concentration.
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Inductively Coupled Plasma Mass Spectrometry (ICP-MS): ICP-MS is a highly sensitive technique that measures the mass-to-charge ratio of ions. The sample is introduced into an ICP, and the ions produced are separated by a mass spectrometer. The abundance of copper ions is measured, providing a quantitative determination of the copper concentration.
4. Calculation:
* The concentration of copper in the extract, determined by AAS, ICP-AES, or ICP-MS, is then used to calculate the copper concentration in the original soil sample, taking into account the weight of soil and volume of extracting solution used.Example:
Let's say after DTPA extraction and ICP-AES analysis, the copper concentration in the extract is found to be 2 mg/L. If you used 10 grams of soil and 20 mL of DTPA solution, the calculation would be:
Copper in soil (mg/kg) = (Copper in extract (mg/L) * Volume of extract (L)) / Weight of soil (kg)
Copper in soil (mg/kg) = (2 mg/L * 0.02 L) / 0.01 kg = 4 mg/kg
Therefore, the copper concentration in the soil is 4 mg/kg.
