Firma:              Thermo Jarrel Ash

Modell:            ICAP 61 E

Kommentar:   Dokumente engl.

INTRODUCTION

The Thermo Jarrell Ash ICAP 61E Trace Analyzer is a simultaneous plasma emission spectrometer. It consists of three modular components: (1) a computer controlled 0.75 meter polychromator capable of accepting up to 63 channels with a fully automated inductively coupled plasma emission source. (2) a floor mounted power unit which provides power to all other components and accessories, with the exception of the optional polychromator vacuum pump; (3) a data acquisition center, which includes the host computer and a printer, and a table on which to place them.

FIGURE 1-1: ASSEMBLED ICAP 61E TRACE ANALYZER SPECTROMETER SYSTEM

THEORY OF OPERATION

INDUCTIVELY COUPLED PLASMA EMISSION SOURCE

The emission source for the ICAP 61E Trace Analyzer spectrometer is an inductively coupled argon plasma (ICAP). The ICAP source is powered by a 2 kW crystal controlled radio frequency (RF) generator operating at 27.12 MHz. The output from the RF generator is coupled to a water­cooled copper induction coil that is wrapped around the outside of a quartz torch assembly.

The largest flow of argon (the coolant flow) passes between the outer and intermediate tubes of the torch. Smaller gas flows pass between the intermediate tube (auxiliary flow), and through the center tube (sample flow).

During plasma ignition, the gas stream is seeded with electrons from an external source, in this case a spark. These electrons are accelerated in a torroidal path by the RF electromagnetic field, and they collide with argon atoms to form more electrons and argon ions, which are in turn accelerated. This process continues until the gas becomes highly ionized (a plasma), at which point the discharge is stable and self-sustaining as long as the RF field is applied. The temperature within this torroidal plasma is as high as 10,000 K.

Liquid samples are introduced into the plasma discharge as an aerosol suspended in argon gas. This sample aerosol is carried through the center tube of the three quartz tubes that comprise the torch assembly. The sample aerosol stream passes through the center of the torroidal plasma discharge, where it is desolvated, atomized, and the resultant elements are excited. After excitation, the atoms that comprised the Sample emit light at their characteristic wavelengths. This light is transmitted to the optical system.

The inductively coupled argon plasma is close to an ideal excitation source. The plasma is inherently very stable over long time periods. It provides a high degree of excitation, resulting in a multiplicity of excitation lines from which to choose. The high density of free electrons ensures that the fraction of an element that is ionized remains constant despite the presence of various matrix constituents. The high temperature and long residence times inhibit anion interferences. The optically thin stream of Sample reduces self absorption to negligible proportions. As a result, the plasma exhibits a dynamic range of up to 6 orders of magnitude. This simplifies sample preparation and often makes serial dilutions unnecessary.

OPTICAL SYSTEM

Light from the plasma emission source is focused onto the entrance slit of the polychromator optical systems. After passing through the entrance slit, the light is dispersed by a diffraction grating. A narrow range of dispersed wavelengths pass through an exit slit and falls onto a photomultiplier tube (PMT) detector. The detector converts light energy to electrical current. The magnitude of the current is proportional to light intensity. The current is integrated over a predefined time period, and this integrated change is measured by the detector circuit and passed on to the host computer.

For the polychromator spectrometer, the wavelengths of light measured by the detectors are determined by the position of the exit slits and photomultiplier tubes on the focal curve. All photomultiplier tubes are read simultaneously.

COMPUTER SYSTEM

The host computer system controls collection of the integrated charge information at each channel and converts this value to concentration units. The host computer also controls the spectrum shifter mechanism, as well as many other parameters associated with the emission source and optical system. The host computer is also used to set up the analytical methods, and to store and retrieve analytical data.

Specification

PLASMA SOURCE:

2kW RF generator, crystal controlled at 27.12 MHz with automatic tuning, power stabilization feed-back loop, and direct coupling (no matchbox).

Built-in peristaltic pump.

Meinhardt concentric glass nebulizer.

Glass spray chamber.

Torch with demountable quartz center tube.

Controlled Parameters:

Output Power:             6 steps from 750 to 1750 W

Auxiliary Argon Flow:   4 steps from off to 1.5 L/min

Nebulizer Argon Pressure:     Continuously variable to 45 psi

Peristaltic Pump Rate:            Continuously variable to 200 rpm (0 to 2.5 mL/min with standard tubing)

COMPUTER SYSTEM:

IBM 386 AT compatible

NEC Pinwriter P2200XE printer, IBM Graphics, or HP Paintjet printer

ThermoSPEC - Spectrometer Operating System

POLYCHROMATOR OPTICS:

0.75 nm Rowland Circle, Paschen-Runge mount. 1510 or 2400 grooves/mm ruled grating at 500 nm

                                      2400 m/mm grating

Linear Dispersion:

First Order                     0.53 nm/mm

Second Order                0.26 nm/mm

Resolution:

First Order                     0.016 nm

Second Order                0.008 nm

Wavelength Range:

Vacuum                         170-500 nm

(Special channels are available for K, Li, and Na determinations with 2400 g/mm. grating).

SIZE AND WEIGHT:

Spectrometer:             69" W x 35" D x 54" H (176 x 89 x 136 cm)

                                    1500 lbs (680 kg) Vacuum

Power Supply.             13" W x 31" D x 24" H (32 x 79 x 61 cm)

                                    200 lbs (91 kg)

Host Computer:           48" W x 30" D x 46" H (122 x 76 x 117 cm)

                                    85 lbs (39 kg)