Assay Sampling Protocols for Industrial Metal Scrap Valuation
Assay sampling protocols establish true dry weight and payable metal content, directly governing settlement values, working capital allocations, and lender borrowing base limits.
Matrix Interference
Meaning
Analytical signal distortion represents the physical or chemical influence of non-target elements in a sample on the measurement of the target analyte. Experiencing matrix interference can lead to either suppressed or enhanced signals in instruments like spectrometers. This issue can result in inaccurate reporting of the metal concentration if the calibration standards do not match the sample composition.
Chemical Effect
High levels of easily ionised elements can change the temperature of the instrument’s plasma. This alteration affects how efficiently the target metals are excited and detected. The signal of the target analyte is often reduced as a result.
This can lead to underreporting the metal values.
Spectral Overlap
The emission lines of different elements can lie very close to one another in the light spectrum. When this happens, a high concentration of an interfering metal can cause a false positive for the target element. This requires the chemist to select alternative wavelengths that are free from interference.
The software must apply background corrections to resolve the issue.
Calibration Adjustment
Matching the chemical composition of the calibration standards to the sample matrix is the best way to prevent this error. This process is known as matrix matching and is standard practice in commercial assays. If the sample matrix is highly variable, an internal standard can be added to the solution to track and correct for changes in the signal.
This step ensures that the final reports are reliable even when testing very complex concentrates.