It's definitely frustrating to see such low recoveries with your CRMs! Here's a breakdown of potential issues and troubleshooting steps to help you get those numbers up:

1. Digestion Efficiency:

* Incomplete Digestion: Soil mineral samples are complex. Ensure your digestion method (likely acid digestion) is completely breaking down the matrix to release the analytes.

* Stronger Acids: Consider using a mixture of concentrated acids (e.g., nitric, hydrochloric, hydrofluoric) if you aren't already. HF is particularly important for dissolving silicate minerals.

* Higher Temperatures/Longer Times: Increase the temperature and/or duration of the digestion.

* Microwave Digestion: If you have access, microwave digestion can provide more efficient and controlled heating.

* Loss of Analytes during Digestion: Some elements (especially volatile ones like sulfur) can be lost during digestion.

* Closed Vessel Digestion: This helps minimize losses.

* Optimize Temperature: Avoid excessively high temperatures.

* Reagents: Check the purity of your digestion reagents.

2. Matrix Effects:

* Interferences: The soil matrix (minerals, organic matter) can cause spectral interferences in ICP-OES.

* Matrix Matching: Prepare your calibration standards in a matrix similar to your samples.

* Internal Standards: Add an element not present in your samples to monitor and correct for matrix effects.

* Background Correction: Use appropriate background correction techniques on your ICP-OES.

* High Total Dissolved Solids (TDS): High TDS in your digested samples can affect the plasma and nebulization efficiency.

* Dilution: Dilute your samples further if necessary. However, be mindful of your detection limits.

3. Instrument Calibration and Performance:

* Calibration Standards: Ensure your calibration standards are accurate and cover the expected concentration range of your samples.

* Wavelength Selection: Choose appropriate wavelengths for each analyte, avoiding spectral interferences.

* Plasma Conditions: Optimize the ICP-OES operating parameters (e.g., RF power, plasma gas flow rates, nebulizer gas flow rate) for your matrix and analytes.

* Instrument Tuning: Regularly tune your ICP-OES to maintain optimal performance.

4. CRM Considerations:

* CRM Compatibility: Verify that the CRM you are using is appropriate for your soil matrix and the elements you are analyzing.

* CRM Preparation: Ensure the CRM is properly stored and prepared according to the manufacturer's instructions.

* CRM Value: Double-check the certified values of the CRM to rule out any discrepancies.

5. Other Tips:

* Blanks: Run plenty of blanks throughout your analysis to monitor for contamination.

* Replicates: Analyze your samples and CRMs in replicates to assess precision.

* Spiking: Spike your samples with known concentrations of the analytes to assess recovery and matrix effects.

* Method Validation: Perform a thorough method validation, including recovery studies, to ensure accuracy and reliability.

Important Notes:

* Sulfur: Sulfur can be particularly challenging in ICP-OES due to spectral interferences and potential losses during digestion.

* Consult with Experts: If you're still struggling, don't hesitate to contact ICP-OES specialists or the CRM manufacturer for advice.

By systematically addressing these points, you should be able to identify the cause of the low recoveries and get your method working effectively. Good luck!