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Eluent, Effluent, Eluate, and Eluite Chromatographic nomenclature can be, well, interesting Quickly now. Without getting out your copy of R. C. Denney's Dictionary of Chromatography, do you know the correct definitions of eluent, eluate, and effluent? If you do, go to the head of the class, because many analytical chemists do not understand the correct definitions of these commonly used chromatographic terms. Our own confusion about these terms led us to question ANALYTICAL C H E M -
ISTRY'S Associate Editor for chromatography, Georges Guiochon of Georgetown University, about their meaning. According to Guiochon, eluent (some times spelled eluant) is the solvent or solvent mixture used in elution chromatography and is synonymous with mobile phase. Eluate is the mixture of solute and solvent exiting the column. Effluent is the stream flowing out of a chromatographic column. "In practice, effluent could be synonymous with eluate," Guiochon explained. "However, effluent is the stream, whether there is a separation taking place or not. The eluate exists only during the course of a separation." A more precise term for the chromatographic solute or analyte is eluite, a term coined by Csaba Horvâth of Yale University around 1980. Eluite, which was designed to sound like the words analyte and solute, refers to a sample component that is being eluted. "Solute is a very broad term," said Horvâth. "Anything in solution—you don't have to be doing chromatography—is still a solute, right? This term eluite immediately tells you that now you're talking about a substance subject to an elution process in a chromatography column." Horvâth sees other problems with the term solute. For example, in adsorption chromatography (as opposed to partition chromatography) the eluite does not dissolve in the stationary phase during the elution process but is rather adsorbed to it. In such a case, the term solute is not precise.
When asked why he feels the new term is needed, Horvâth explained that "the word eluite makes it much more precise and convenient to talk from the physical chemical or theoretical point of view about a sample component undergoing the chromatography process. When you talk about this thing it seems to be much clearer. Because the
WW There are an enormous number of terms introduced in chromatography papers, but only a fraction of those make it in the language at l a r g e . · · alternative would be either analyte or solute. Analyte applies only when you do a chromatographic analysis. But if I do a physicochemical investigation by using chromatography I don't do an analysis and I don't have analytes. I don't have solutes either. The solute can be anything. I mean, I dissolve a lot of other compounds in my eluent. Salts and additives are also used. Why would I call only one a solute? I felt that more precisely we could call it an eluite." Eluite is still a rare term. "I don't know how many other people are using it," said Horvâth. "It usually takes quite a bit of time for such a word to catch on." Horvâth was somewhat more successful when he invented the term isocratic some years ago. After introducing the word for the first time in a lecture, he walked outside the meeting room to the exhibit area, where an instrument salesman was already trumpeting his company's chromatograph as having been specially designed for isocratic chromatography. "He heard the word in the lecture and immediately turned it into a sales pitch," recalled Horvâth. "I was really amazed. Indeed, weeks later people used it. If the time is right, the word is right, and there is a need for it, then it can be adopted very quickly." The discussion of eluite brings earli-
er controversies to mind. "In the old time," Horvâth explained, "chromatogram was a physical entity, the compounds separated in the column. When Giddings started to write his papers on chromatography, I remember he used the term chromatogram for the physical reality, not for this recording of the concentration profiles on a piece of paper. "When Kovâts wrote his paper on the Kovâts index," Horvâth said, "he spent the introductory part of it saying that in gas chromatography what we have is really not a chromatogram in the definition of the previous generation, that it should be called eluogram, because it is as a result of elution that the stuff comes out of the column. Eluogram didn't make it either." "There are an enormous number of terms introduced in chromatography papers," said Horvâth, "but only a fraction of those make it in the language at large. You can coin a new word, but if people don't like it for one reason or another, they don't take it." Stu Borman
ALMA Meets at Pitt The University of Pittsburgh was the site of this year's annual meeting of the Analytical Laboratory Managers Association (ALMA), and what a site it is. The university, with its spectacular Cathedral of Learning and many other examples of fine architecture, is an inspiring location for a scientific meeting. With most of the ALMA sessions held in the beautifully renovated William Pitt Union in a room that resembles Versaille's Hall of Mirrors and with luncheon served in the enclosed courtyard of the Frick Fine Arts Museum, this year's ALMA meeting was indeed a class act. One major advantage of the relatively small scale of ALMA meetings—an attendance of about 100 is typical—is the opportunity afforded for freewheeling discussions among members
ANALYTICAL CHEMISTRY, VOL. 59, NO. 2, JANUARY 15, 1987 · 99 A
