Alignment

The exact locations of NMR peaks can change with various chemical factors and matrix effects, such as changes in pH or metal ion content. As such, peaks don't line up exactly. This complicates the quantification process. Fortunately, several methods exist for aligning the same peaks across different spectra, and we utilize several of these in our toolbox. They can be grouped into three categories of algorithms:

Star Methods align to a reference spectrum, and include the following algorithms: CCOW, PAFFT, RAFFT, ICOSHIFT, and PARCCOW (parallelized CCOW).

For 2D: star_align2D

[HCA-based (HATS-like) Methods](https://github.com/artedison/Edison_Lab_Shared_Metabolomics_UGA/wiki/guide_align1D) group the spectra by HCA and align the most similar ones first, combining groups as the algorithm proceeds. PAFFT, RAFFT, ICOSHIFT, and CCOW.

For 2D: HATS

Multi-Align Workflow (combined methods), only for 1D

Additional Refs:

Vu, Trung Nghia, and Kris Laukens. “Getting Your Peaks in Line: A Review of Alignment Methods for NMR Spectral Data.” Metabolites 3, no. 2 (2013): 259–76. https://doi.org/10.3390/metabo3020259.