PLS is a basic tool of chemometrics and there are never too many articles helping its understanding. The attention should be pointed to newest article  about PLS1 geometry. This is a great companion to earlier paper  about nine PLS algorithms.
- U.G. Indahl, "The geometry of PLS1 explained properly: 10 key notes on mathematical properties of and some alternative algorithmic approaches to PLS1 modelling", Journal of Chemometrics, vol. 28, pp. 168-180, 2014. http://dx.doi.org/10.1002/cem.2589
- M. Andersson, "A comparison of nine PLS1 algorithms", Journal of Chemometrics, vol. 23, pp. 518-529, 2009. http://dx.doi.org/10.1002/cem.1248