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5 0 6 A . ANALYTICAL CHEMISTRY, VOL. 57, NO. 4, APRIL 1985
Column efficiency measurement Sir: The authors of "Column Efficien cy Measurement" (Bidlingmeyer, Bri an Α.; Warren, F. Vincent, Jr. Anal. Chem. 1984,56,1583-96 A) made a se rious omission in their Table II, "Cal culation methods for column efficien cy used by LC column suppliers." Brownlee (now a Division of Ap plied Biosystems) was not mentioned, and although Brownlee is not current ly a major LC column supplier, it has been using the moments method for calculating column efficiency on its columns since 1977. In fact, Jerry Higgins of Brownlee has been a strong proponent of the moments method. He has given seminars and Pittsburgh Conference talks and has written ap plication notes explaining the method. The same table points out that none of the other column manufacturers provide accurate column efficiencies. This is surprising, because data sys tems that will automatically perform these calculations are available for rel atively low cost from Nelson Analyt ical. Glenn I. Ouchi Nelson Analytical 10061 Bubb Rd. Cupertino, Calif. 95014 Reply: As the text indicated, Table II was intended to list methods of var ious suppliers to give the readers a feel for the range of methods used. Pres ently there are over 65 suppliers of LC columns, and we apologize for not list ing a favorite of any of the readers. We are not under the impression that "none of the other column manu facturers provide accurate column ef ficiencies," as Dr. Ouchi writes. The situation is that a variety of calcula tion methods are used and that some of these are potentially less accurate when used under adverse conditions. As stated in the text, "If the test peak is truly Gaussian, each of the calcula tion methods will give the same [effi ciency] results." In this sense, every method is "correct" for calculating plate counts. However, each has par ticular strengths and weaknesses, and it is important that a user recognize this and use each method appropriate ly. Brian A. Bidlingmeyer F. Vincent Warren Waters Chromatography Division of Millipore Maple St. Milford, Mass. 01757
