For Soft X-ray-VUV-UV Spectroscopy
2-ÎdJiïmj &HJOU2WQ InjadmcA tk&t CUMQA Û& uKU^Wjtb, gap ...p/iemely This exclusive McPherson grazing incidence scanning monochromator and spectrograph gives you a unique capability. Now, you can scan photoelectrically, or photograph, from the soft X-ray (lOA) through the UV [2500A). And achieve first order resolution of better than 0.3Â with the standard 300 L/mm grating. Proportionately improved resolutions can also be achieved with the optional 600 L/mm and 1200 L/mm gratings. Its versatility is further enhanced by an adjustable angle of incidence which may be set from 82° to 88° and the rapid interchangeability of the kinematically mounted gratings. This means that you can literally choose the exact wavelength coverage and resolution you need. The basic modular design of the Model 247 allows quick, simple
conversion from monochromator mode to spectrographs mode. As a monochromator, the Model 247 is an excellent source of radiation for studies such as ionization and dissociation where photon energies from 5 to above 1240 electron volts are required. As a spectrograph, a camera attachment replaces the monochromator scanning slit and a vacuum chamber encompasses the 30-inch focal curve. The Model 247 is especially appropriate for aerospace researchers and scientists, plasma and nuclear physicists. McPherson offers a complete line of precision instruments for accurate analysis of the spectral range from soft X-ray to near IR. For complete information on the versatile Model 247 grazing incidence combination Monochromator/ Spectrograph, write or call.
Agent for U.S.A., McPherson offers the book ESCA by Kal Siegbahn et al, an important new work on electron spectroscopy for chemical analysis. $25.20 per copy.
MCPHERSON I N S T R U M E N T C O R P O R A T I O N 530CMain Street, Acton, Massachusetts 01720 · 617-263-7733 Circle No. 131 on Readers' Service Card 112 A
·
ANALYTICAL CHEMISTRY
rial between the plates. The best use is made of this technique, therefore, when the polarity of sample and solvent are widely different. The detector portion consists of a pair of parallel plates or concentric cylinders in close proximity through which the effluent is directed. An alternating potential in the range of 10 to 100 megahertz is applied to the cell connected in a standard capacitance bridge circuit. Dielectric constant is the electrical analog of refractive index and so exhibits much the same advantages and disadvantages. As would be expected, use is not recommended with gradient elution techniques particularly if the gradient is a function of solvent polarity. The practical minimum sample size is in the one to ten milligram range. Response is linear with concentration over several decades so direct quantitation with area analysis is possible. To date the best use for this technique has been made with gel filtration chromatography. Summary and Discussion
The use of a suitable detector to monitor liquid effluent is an important first step in reducing the time and effort required to develop and utilize liquid chromatographic procedures. In the absence of a true universal detector, however, certain tests must be performed on typical dilutions of sample in carrier so that a proper decision can be made on the choice of detector. Monitors such as refractive index, ultraviolet absorption, and electrolytic conductivity are readily evaluated for application on their laboratory counterparts. Heat of adsorption requires some experimentation to establish detection limits but is an excellent choice for general use where absolute quantitation is not essential. Flame ionization offers sensitivity, quantitative response, and freedom from baseline drift with gradient elution. This detector should be a first choice when working with low volatility samples. Special purpose detectors such as visible absorption, radioactivity, and fluorescence are used where the chemical system dictates. Research in detectors is proceeding along predictable lines utilizing classical instrumental principles such as polarography, fluorescence, and dielectric constant. For the most part they are special purpose devices in that they utilize a specific chemical property or functional group. It is reasonable to assume that certain individual detectors will demonstrate a particular utility for a given area of liquid chromatography such as electrolytic conductivity and refractive index have
