Books
Predicting Retention in LC cult. One of the reasons that compendial methods now specify a column type (e.g., USP Type LI) and then require the user to obtain at least a minimum set value of resolution between main component and common impurities is the difficulty of transferring methods between labs and/ or columns. The introductory paragraphs of Chap ter 12 deal with the use of multivariate methods. This chapter also gives a good Retention and Selectivity in explanation of the techniques used and the Liquid Chromatography: "soft-model" nature of factor-analytical Prediction, Standardisation approaches, shows some examples of suc and Phase Comparisons cesses, and discusses some of the tools Roger M. Smith, Ed. available. The very nature of factor analyti Elsevier Science Publishers cal methods (that the observed variation 655 Avenue of the Americas can be explained by a progression of ei New York, NY 10010 genvectors) makes it the least directly 1995, 478pp., $265.75 "molecular" in its results. But then these same methods are the basis of many of the One of the goals of the many efforts to precommonly used molecular structure pre dict retention is to relate physical and diction programs now preferred by practic chemical factors to the observed changes ing chemists. in selectivity and retention with solvent and column type. These efforts overlap The reader should remember that cor and parallel those that use chemometric relation does not guarantee a causal rela methods such as factor analytical target tionship. Models such as topological shape prediction methods and heavily modeled and surface area correlate to molar vol formalisms based on linear, free-energy asume, which correlates to polarizability and sumptions. The goal is both scholarly and the London force contribution to sorp practical. tion energetics in RPLC. Sorption is a freeis no simply defined void volume for energy change-described process. Linear From a scholarly view, the influence of RPLC, using retention indices is compli free-energy relations prove little except molecular weight, size, structure, and cated. functionality on retention is a fascinating Many workers have demonstrated that that things related to the total freeenergy change in a given process are pro topic. For the practicing scientist whose in- each molecular type has its unique dead portional to each other and that they cor terest in any chemical separation method volume. However, as the total retention is the outcome, the goal is to minimize the volume grows large and the net retention relate. This does not imply that one factor causes the other. Hence, it is possible to effort involved in designing a new or volume grows with respect to any range relate octanol-water partition values (Kov/) modified separation method. Certainly, of void volumes, this becomes less of a the vast majority of chromatography users problem, and it is possible to calibrate a to net retention in RPLC and to correlate octanol-water partition to hydrophobicity fall into this category. They want quantita- given column with homologs of a given measured in other ways. Onefinds,how tive answers or separate vials of comchemical class and then confirm the iden ever, that such correlations are only for pound A, B, C, and so on. tity of one of those homologs relative to This book willfilla gap for the practic- its behavior. But the dead volume is a func compound classes in any precise sense. Families of straight lines are found in plots ing scientist curious about progress in re- tion of solvent composition, the manufac of many different compounds: Kovf values turer of the column packing (all Clg tention prediction based on chemical versus their RPLC retention values. columns are not the same), and other structure or chemically related parameparameters. Therefore, the transfer of cali ters. The introductory chapter is espeA good book, worth having at hand. bration methods, lab to lab or column cially well written. The majority of chapReviewed by C. H. Lochmuller, Duke source to column source, is rather diffi ters relate some form of retention index University, Durham, NC method to the prediction of behavior. Add to this the chapters by Sanders and Wise on their work in RPLC phase structure and selectivity for polyaromatic hydrocarbons, Pesek and Williamsen on novel phases, and afinalchapter by Bolck and Smilde on multivariate methods, and you have a valuable tertiary reference. This book discusses recent progress in transferring the Kovàts method developed for GC to LC, and especially RPLC, an effort that began in the early days of modern HPLC. Retention indices help identify compounds, confirm the identity of anticipated compounds, and determine the influence of the branching of chains, changing functionality, and positional isomerism. Unfortunately, because there
This book will fill α gap for the practicing scientist
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Analytical Chemistry, November 1, 1995
