Paschen-Runge spectrometer

Fig. 19. Important optical mountings for optical spectrometers with a plane (A Ebert, B Czerny-Turner) and a concave (C Seya-Namioka, D Paschen-Runge) grating, m Mirror, se entrance slit, sa exit slit, gp plane grating, gc concave grating.

Tab. 6. Analytical precision of spark ablation ICP-OES for a BAS 410/1 steel sample, ccu = 3.6 mg/g. Line pair leu 324.7 nm/lfe 238.2 nm- 400 Hz medium voltage spark, 1.5 kW argon ICP, transport gas flow 1.2 L/min, 0.5 m Paschen-Runge spectrometer, measurement time 10 s [213],...

Fig. 93. ICP-OES spectrometer CIROS-Paschen-Runge circle with detector alignement. (Courtesy of Spectro Analytical Instruments.)...

The spectrometers used are adapted either for sequential or simultaneous multi-element measurements. Commonly used grating spectrometers in plasma AES include (i) spectrometers with the Paschen-Runge mount, (ii) echelle spectrometers, (iii) spectrometers with Ebert and Czerny-Turner mounts, (iv) spectrometers with Seya-Namioka mounts, and (v) double monochromators. Also Fourier transform spectrometers may be used in plasma AES. 

The slit position and its relation to the angle of incidence should be chosen to take advantage of the highest reflectivity of the grating. The spectral order desired also must be considered. Some Paschen-Runge spectrometers have two fixed slits. By using angles of incidence of about 20° and 50°, both... 

FIGURE 4-14. Optical diagram of a "folded" Paschen-Runge spectrometer. 

Spectrometer designs are similar to those already discussed, including broadband diode array, echelle, Czerny-Turner, and Paschen-Runge spectrometers, with miniature echelle and CCD array systems most suited to portable LIBS systems. The LIBSCAN 25+ (Applied Photonics Ltd.) uses up to 6 compact CCD array spectrometers covering the 185-900 nm range. Figure 7.53 shows the field-portable LIBSCAN 25-I-. 

Computer-controlled stepper motors are used to turn the grating. Their angular resolution is often above 10(X) steps per turn. For a so-called sinebar drive, the number of steps performed by the motor is directly proportional to the wavelength displacement, A pen recorder is running off on the spindle driven by the motor. A further approach is to u.se a Paschen - Runge spectrometer with equidistant exit slits and a detector moving in the focal plane. Fine adjustment of the lines is by computer-controlled displacement of the entrance slit. 

Simultaneous Spectrometers. Modem simultaneous spectrometers use photoelectric radiation detection rather than the photographic plates formerly used for qualitative and semi-quantitative analyses. Simultaneous photoelectric spectrometers mostly have a Paschen -Runge optical mounting. They have many exit slits and are especially suitable for rapid determinations of many elements in a constant, well-characterized matrix the achievable precision is high. However, the... 

A further system uses a Paschen-Runge spectrometer with equidistant exit slits and a detector moving along the focal plane. Fine adjustment of the lines is then done by computer-controlled displacement of the entrance slit. 

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