Identifying Organic Contaminants in Sub Tier Castings Using FTIR Fingerprinting
Attenuated total reflectance FTIR identifies organic parting agents on raw castings before expensive coating processes fail on customer lines.
Spectral Subtraction
Meaning
Mathematical processing techniques used to isolate the signal of a single component from a complex mixture allow for more precise analysis of industrial materials. By employing spectral subtraction, a technician can remove the contribution of a known solvent or polymer matrix from a raw scan. This reveals the hidden features of additives, contaminants or secondary components that would otherwise be obscured.
Computational Method
Digital data from a reference spectrum is multiplied by a scaling factor and then subtracted from the sample spectrum point by point. During spectral subtraction, the operator adjusts the factor until the characteristic peaks of the background material disappear. This process requires a high degree of precision to avoid over-subtraction, which creates negative peaks and distorts the remaining data.
Modern software uses automated algorithms to find the optimal null point for common solvents.
Component Isolation
Separation of overlapping signals is the primary goal when analyzing multi-component systems like lubricants or composite materials. Using spectral subtraction makes it possible to identify the specific type of oxidation or degradation products in used engine oil. It also facilitates the detection of low-concentration stabilizers in plastic formulations.
This method is especially useful when physical separation of the components is difficult or time-consuming.
Analytical Boundary
Accuracy of the results is limited by the linearity of the detector and the reproducibility of the sampling technique. Because spectral subtraction relies on the assumption that the components do not chemically interact, its use is restricted in systems with strong inter-molecular bonding. In Chinese regulatory laboratories, this technique supports the identification of restricted substances under the RoHS directive.
The final claim about the composition must be supported by the original raw data to ensure the integrity of the audit trail.