a Based on the concentration of material necessary to produce a signal twice the standard deviation of the random background noise. b Based on 10-µ1 sample.oxide-acetylene flame for any of the metals assayed, including chromium. The temperature change in the nitrous oxide-acetylene flame when aspirating different quantities of liquids apparently shows little or no effect on the free atom fraction in the flame.Detection Limits. In order for the AAS detector system to be useful in liquid chromatographic work, the detector must be both selective and sensitive. The selectivity and sensitivity of conventional AAS work has been well noted (10). This selectivity also applies to AAS when used as an LC detector and, while the range of compounds for which it is suitable is not as wide as other LC detectors, its specificity far surpasses that of other detectors. Difficulties can arise when using the detector for assays of several different metals, since lamp and burner changes are necessitated. Chromatograms of several species containing the same metal are, however, ideally suited for the detection system.The detection limits of this system were measured in the conventional manner, i.e., the concentration of material necessary to produce a signal twice as large as the standard deviation of the random background noise.The detection limits for several of the transition metals in both organic and aqueous phases are presented in Table IV. These values are applicable under the experimental conditions used and may be improved under more nearly optimum conditions. The conditions of the AAS, such as sensitivity and gain of the electronics, and adjustment of concentration control on the Perkin-Elmer AAS may allow lower detection limits for selected metals.Generally speaking, solutions containing metals in the mg/1. (part per million) range are satisfactory for this type of detection.The use of organic mobile phases requires some modification of the AAS for optimum performance. When aspirating organics, the three-slot burner head gave significantly better results than did the standard single-slot burner. A "hotter" (lower fuel-air ratio) flame could be generated with the three-slot burner, because of its ability to cope with a higher gas flow without excessive instability. The absolute detection limits in Table III are based on a 10-µ1 sample. Use of a larger sample loop would, of course, lower these figures.

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