arc and spark techniques

Question 1

what do non-flame emission sources mainly consider?

Answer 1

plasmas - high ionisaed gas

Question 2

How is plasma usually obtained?

Answer 2

by subjecting the gas to an electrical discharge

Question 3

What are direct current arc plasmas?

Answer 3

high constant current passed through argon gas between 2/3 electrodes

Question 4

What current does ICP rely on? in presence of what?

Answer 4

high frequency alternating current in presence of argon

Question 5

What current does MIP rely on? in presence of what?

Answer 5

very high frequency alternating current in presence of helium?

Question 6

ARC and spark emission is alternative to what?

Answer 6

excitation to flames

Question 7

In arc/spark emission, where does sample excitation occur ?

Answer 7

in gap between pair of electrodes

Question 8

What does the passage of electricity from electrodes through the gap provide?

Answer 8

the energy to atomise sample and excite resulting atoms to higher electronic states

Question 9

what are the discharges like in spark, which is both AC and DC?

Answer 9

short lived at several thousand volts

Question 10

What do the direct current arc techniques refer to?

Answer 10

electrical discharge between 2 electrodes typically 10 amps at 10-100Volts

Question 11

what do the alternating current arc techniques refer to?

Answer 11

same as DC arc but pulsed at 50-500Hz

Question 12

which of AC and DC arc is cooler and more sensitive? and which is better for precision analysis?

Answer 12

AC arc

Question 13

What is an application of Arc/spark emission sources?

Answer 13

can be used for direct analysis of metal samples using sample as anode and a counter electrode as cathode

Question 14

What is step 1 of arc spark method?

Answer 14

one or more stds run in place of sample to produce calibration data

Question 15

What is step 2 of arc spark method?

Answer 15

sample is run, conc estimated

Question 16

What is step 3 of arc spark method?

Answer 16

due to variability in arc/spark, method of internal stds is often used for calibration

Question 17

What is used instead of normal internal standards?

Answer 17

a major element in the sample is chosen and assumed its concentration is invariant

Question 18

in arc sources, how far apart are electrodes spread?

Answer 18

1-20mm

Question 19

The arc is initially ignited by a low current spark causing what?

Answer 19

formation of ions for electrical conduction in the gap

Question 20

What maintains the current once the arc is struck?

Answer 20

thermal ionisation

Question 21

the 2 electrodes can also be brought together to provide what?

Answer 21

heat for ionisation - then separated to desired distance

Question 22

Spark techniques are commonly used in what industry?

Answer 22

iron, steel and aluminium industries for rapid analysis of metals and alloys

Question 23

Why are vacuum monochromators required?

Answer 23

as C, P and S are routinely monitored

Question 24

what are the detection limits?

Answer 24

poor, 10-100ppm

Question 25

Non-conducting samples, such as liquids, are usually analysed by what method?

Answer 25

arc

Question 26

What are the liquid samples supported on?

Answer 26

disposable graphie electrode

Question 27

what are 2 limitations of these methods?

Answer 27

matrix effects, well mathced stds required for a good quantitative analysis