1.1 Inductively coupled plasma (ICP)

Three Argon flow

1. Plasma gas (10-20 L/min)

2. Nebulizer gas (~1L/min)

3. Optional auxiliary gas (~0.5L/min)

Radio-frequency (RF) power source up to 2kW

Higher temp (~8000K)

Heated from outside-in

Torch up to 1 “ diameter

Plasma structure• Brilliant white core – Ar continuum

radiation• Flame-like tail up to 2cm• Transparent region (15-20 mm above

the core) – measurement made

• Analyte atoms have 2 ms residence time and experience temperature from 5000-800K. Atomized in “inert” atmosphere. Little ionization.

• Torch may be viewed radially or axially

Sample introduction

1. Nebulizer – convert solutions to fine spray or aerosol

- Ultrasonic nebulizer uses ultrasound waves to boil solutions flowing across disc

- Pneumatic nebulizer uses high pressure gas to entrain solution

2. Electrothermal vaporizer (ETV)

Electric current rapidly heats crucible containing sample

Sample carried to atomizer by Ar or He

Only for introduction, not atomization

3. Other methods

Direct insertion {powder placed inside flame, plasma, arc or spark atomizer}

Laser ablation {uses laser to vaporize sample}

1.2 Direct current plasmaDC current 10-15 A between C anode and cathode

Plasma core at 10,000 K, viewing region at 5,000 K

Simple, less Ar than ICP

1.3 Plasma source spectrophotometer

1.3.1 Sequential (scanning and slew-scanning)Slew-scan spectrometers – Rapidly scan (slewed) across blank regions

Slowly scann across lines

Computer control/preselected lines to scan

1.3.2 Multichannel spectrometer

1.4 Plasma AES vs. Flame AAS

AAS AESSimilar atomization technique to AES

Addition of radiation source

High temperature for atomization Very high temperature for excitation

(flame and electrothermal atomization) (plasma/arc/spark)

Low cost instrumentation moderate-high cost

Single element simultaneous multielement analysis

Quantitative qualitative and quantitative

Low sample throughput high sample throughput

Atomization interference spectral interference (large # of lines)

Detection limit 0.001-0.020 ppm 10ppb

Greater precision

complementary technique

Limited to qualitative/semi-quantative analysis (arc flicker)

Usually performed on solids

Largely displaced by plasma-AES

Sample pressed into electrode

Electric current flowing between two C electrodes

Cyanogen bands (CN) 350-420 nm occur with C electrode in air – He, Ar atmosphere

Fig. 10-17 (p.270)

Graphite electrode shapes

Arc/spark unstable – each line measure >20 s (needs multichannel detection)

Photographic film

- Cheap

- Long integration times

- Difficult to develop/analyze

- Non-linearity of line “darkness”

Multichannel PMT instrument- For rapid determinations (< 20 s) but not versatile- Routine analysis for solids – metals, alloys, ores, rocks, solids- Portable instruments

Spectrographs (record spectrum with a photographic plate at the focal plane)