arc and spark techniques Flashcards
what do non-flame emission sources mainly consider?
plasmas - high ionisaed gas
How is plasma usually obtained?
by subjecting the gas to an electrical discharge
What are direct current arc plasmas?
high constant current passed through argon gas between 2/3 electrodes
What current does ICP rely on? in presence of what?
high frequency alternating current in presence of argon
What current does MIP rely on? in presence of what?
very high frequency alternating current in presence of helium?
ARC and spark emission is alternative to what?
excitation to flames
In arc/spark emission, where does sample excitation occur ?
in gap between pair of electrodes
What does the passage of electricity from electrodes through the gap provide?
the energy to atomise sample and excite resulting atoms to higher electronic states
what are the discharges like in spark, which is both AC and DC?
short lived at several thousand volts
What do the direct current arc techniques refer to?
electrical discharge between 2 electrodes typically 10 amps at 10-100Volts
what do the alternating current arc techniques refer to?
same as DC arc but pulsed at 50-500Hz
which of AC and DC arc is cooler and more sensitive? and which is better for precision analysis?
AC arc
What is an application of Arc/spark emission sources?
can be used for direct analysis of metal samples using sample as anode and a counter electrode as cathode
What is step 1 of arc spark method?
one or more stds run in place of sample to produce calibration data
What is step 2 of arc spark method?
sample is run, conc estimated
What is step 3 of arc spark method?
due to variability in arc/spark, method of internal stds is often used for calibration
What is used instead of normal internal standards?
a major element in the sample is chosen and assumed its concentration is invariant
in arc sources, how far apart are electrodes spread?
1-20mm
The arc is initially ignited by a low current spark causing what?
formation of ions for electrical conduction in the gap
What maintains the current once the arc is struck?
thermal ionisation
the 2 electrodes can also be brought together to provide what?
heat for ionisation - then separated to desired distance
Spark techniques are commonly used in what industry?
iron, steel and aluminium industries for rapid analysis of metals and alloys
Why are vacuum monochromators required?
as C, P and S are routinely monitored
what are the detection limits?
poor, 10-100ppm
Non-conducting samples, such as liquids, are usually analysed by what method?
arc
What are the liquid samples supported on?
disposable graphie electrode
what are 2 limitations of these methods?
matrix effects, well mathced stds required for a good quantitative analysis
