manufacturer:       Perkin Elmer

model:                   AAnalyst 100

annotation:           Dokumente engl.

The AAnalyst 100 Atomic Absorption Spectrometer is designed for use

with flame absorption, flame emission, graphite furnace, and mercury/hydride atomic absorption techniques.

The AAnalyst 100 offers a high efficiency burner system using an adjustable Universal GemTip corrosion-resistant, plastic nebulizer for general, all-round use where a wide variety of sample types is analyzed. The optional High Sensitivity GemTip nebulizer is available for those applications requiring the utmost in sensitivity and detection limits.

Built-in gas controls with safety interlocks, automatic ignition button on the keypad, and automatic switching from an air-acetylene flame to a nitrous oxide-acetylene flame, simplify operation while insuring operator safety.

A built-in control panel, with a two-line alphanumeric display, a numeric keypad, and function keys, is used to access the comprehensive programming which is embedded in the built-in microprocessor.

The following sections provide a general discussion on the theory of operation and a description of the components of the system, the atomizers, and accessories available with the AAnalyst 100 Spectrometer.

Spectrometer

The spectrometer provides a means of measuring Iight at a specific wavelength. To perform this function, the spectrometer uses a primary light source, a monochromator, and a detector. The primary light source, either a hollow cathode or electrodeless discharge lamp, is placed in the spectrometer to emit the narrow atomic lines of the element to be determined. The light passes through the sample compartment and is absorbed by the atomized sample.

The monochromator disperses the various wavelengths of Iight and isolates the particular line of interest. A dual-blazed grating is used, which provides excellent

performance over the entire atomic absorption wavelength range.

The light leaving the monochromator is directed onto the detector, a photomultiplier tube (PMT), which produces an electrical signal proportional to the light intensity. The electrical signal is amplified and processed to produce a signal which is a measure of the light attenuation occurring in the sample compartment.

The spectrometer uses a deuterium arc lamp to correct for background absorbance caused by non-atomic species in the atom cloud.

When the continuum source background corrector is used, two alternating sets of measurements are made: one with the primary source and a second with the background corrector source. The primary source measures a combination of background and atomic absorption. The continuum source measures only the background. The difference between the two measurements yields the atomic absorption.

Atomizers

The atomizer provides the thermal energy necessary to dissociate chemical compounds, thus providing free analyte atoms so that atomic absorption can occur.

The various types of atomizers available for the system include:

• burner system;
• graphite furnace; and
• heated quartz cell for mercury/hydride determinations.

Burner System

The Perkin-Elmer burner system consists of a nebulizer, burner mixing chamber, burner head, drain system, and built-in manual gas controls with a safety interlock system. The AAnalyst 100 uses an adjustable Universal GemTip corrosion-resistant, plastic nebulizer for general, all-round use. In the burner chamber, the sample is thoroughly mixed with the oxidant-fuel mixture before ignition takes place.

Burner Operation, including flame ignition and shutoff, is controlled through the instrument control Panel.

Operating parameters are entered and stored in the instrument's memory, and then implemented during analysis, except when the system is operated with a computer which then maintains the operating parameters. When operating with a computer, using the AA WinLab software, refer to Chapter 15, Operating the AAnalyst 100 with AA WinLab, in this manual.

Graphite Furnace

The Perkin-Elmer graphite furnace consists of a furnace and Power supply. The sample is placed inside the graphite tube, usually on a L'vov platform, and the tube is electrically heated to atomize the sample. A continuous flow of inert gas inside and outside the tube protects the tube from air oxidation and flushes out the gaseous products. The furnace is water-cooled, via tap water or a water cooling system, to maintain the furnace temperature and to cool it between analyses.

Operating parameters are entered and stored in the instrument's memory, and then implemented during analysis, except when the system is operated with a computer which then maintains the operating parameters.

Mercury/ Hydride System

Mercury/hydride systems are used to determine mercury and the hydride-forming elements. The basic components of a mercury/hydride system are the reaction vessel and sampling cell. The sample solution reacts with a reducing agent in the reaction vessel. A spontaneous reaction occurs to form the gaseous hydride or reduce mercury to its elemental form. The gaseous products are carried to the sample cell, a quartz cell placed in the light path of the spectrometer. The quartz cell is heated to dissociate the hydride gas into free atoms, or in the case of mercury, to prevent condensation of the water vapor.

Perkin-Elmer offers a manual system. In manually operated units, the quartz cell is heated by the flame. Key operating parameters are controlled by the instrument control panel. Data collection as well as calibration and calculation functions are performed by the instrument or the software, when an optional computer is connected. Our manual system is the MHS-10 Analyzer. The MHS-10 analyzer assembly is freestanding and is located next to the sample compartment of the spectrometer. This assembly includes a reaction flank, a reservoir for the reducing agent, and all pneumatic components for control of the carrier gas and transport of metallic vapors to the quartz cell. The cell assembly consists of a quartz cell and a mount. The mount installs on the burner head, permitting the quartz cell to be heated in the flame.

In addition, the Perkin-Elmer flow injection system, which includes a quartz cell and heating mantle, can be used as a fully automated mercury/hydride system. The sampIe is injected into a carrier stream and combined with the reductant in a chemifold. The resultant hydride gas is separated from the solution in a gasliquid separator and carried by a flow of argon gas to the quartz cell, where it is heated. A program is recalled by use of the instrument controller and the analysis is then performed.

Flow Injection System

Flow Injection Analysis (FIA) is used to inject an exact, reproducible volume of sample into a continuously flowing liquid carrier stream. Flow Injection Analysis can be used:

• as a fully automated sample preparation system for mercury/hydride analyses, reagent addition, dilution, analyte preconcentration, and other preparatory procedures;
• for direct analysis of solutions with a high dissolved solids content; and
• for microsampling capabilities when performing flame analyses.

The Perkin-Elmer Flow Injection Analysis System (FIAS) includes peristaltic pumps, a flow injection valve, chemifold, gas/liquid separator, and tubing. The flow injection valve is used to inject the sample solution into a carrier stream. Different sized injection loops are available to accommodate different injection volumes. The chemifold is used to combine different fluid streams to allow reaction, dilution, or matrix modification.

When the AAnalyst 100 is configured without a computer, the flow injection system is fully controlled by the instrument. Several preprogrammed methods are stored in the FIAS memory and are accessed using three or four keystrokes on the instrument control panel. When a computer is added, the restriction on the maximum number of programs is removed.

Autosamplers

Autosamplers are instrument-controlled, multipurpose sampling systems. An autosampler has removable trays for easy sample loading. Once the tray is loaded, the sample is automatically pipetted using a probe placed in a mechanically operated sampling arm.

Some of the features you can perform using an autosampler include:

• running standards to calibrate and recalibrate the instrument;
• introduce a matrix modifier into the graphite furnace;
• running check samples to check instrument performance (if you are running with the AA WinLab software); and
• rinsing between samples (if you are running with the AA WinLab software).

Graphite Furnace Autosampler

The graphite furnace autosampler, used for furnace analyses, includes an 80- position tray and a 40-position autosampler tray. The graphite furnace autosampler is powered by the HGA Power Unit and controlled by the software through the IEEE-488 Interface. In addition, connection to the optional computer, running AA WinLab software, allows wide flexibility in placement of solutions in the sample tray.

AS-90 Autosampler

The AS-90 autosampler is used for flame or FIAS analyses. When using the AS-90 autosampler, you need to select the appropriate autosampler tray. The last sample Position will vary depending upon which autosampler tray you have selected. The letters A - G represent autosampler trays A, B, and C (applicable to the AS-90) and trays E, F, and G (applicable to the AS-91). Autosampler trays A, B, and C represent 1, 2, and 3, respectively, while autosampler trays E, F, and G represent 5, 6, and 7, respectively. Depending upon which autosampler you are using, select the appropriate autosampler tray. Do this by entering the number corresponding to your autosampler tray, then press [Enter].

SELECT AS-90/91 TRAY

(A=1 .. G=7): →--

AS-91 Autosampler

The AS-91 autosampler is used for flame or FIAS analyses. When using the AS-90 autosampler you need to select the appropriate autosampler tray. The last sample position will vary depending upon which autosampler tray you have selected. The letters A - G represent autosampler trays A, B, and C (applicable to the AS-90) and trays E, F, and G (applicable to the AS-91). Autosampler trays A, B, and C represent 1, 2, and 3, respectively. While autosampler trays E, F, and G represent 5, 6, and 7, respectively. Depending upon which autosampler you are using, select the appropriate autosampler tray. Do this by entering the number corresponding to your autosampler tray, then press [Enter].

SELECT AS-90/91 TRAY

(A=1 .. G=7): →--

Optional Computer System

The optional computer controls the hardware components and collects, processes, and stores the analytical data. The computer processes the signals received from the spectrometer to produce a readout of sample concentration.

The computer system specified by Perkin Elmer includes the computer itself, monitor, keyboard, mouse, and an optional printer. The computer communicates with the spectrometer, atomization system, and other system components through an IEEE-488 interface. Refer to Chapter 5, The Computer, in the AAnalyst 100/300 Hardware Guide for more information on the computer. Also, refer to chapter 15, Operating the AAnalyst 100 with AA WinLab, in this manual.