1 In-house Training on ICP-MS

ICP-MS??? Inductively Coupled Plasma Mass Spectrometry or ICP-MS is an analytical technique used for elemental determinations. An ICP-MS combines a high-temperature ICP (Inductively Coupled Plasma) source with a mass spectrometer. The ICP source converts the atoms of the elements in the sample to ions. These ions are then separated and detected by the mass spectrometer.

Atomic Spectroscopy Techniques Three techniques share the same basic components Atomic Absorption (Flame and Furnace) ICP-AES ICP-MS All three are used for the analysis of metals

Comparison of Techniques ICP-MSICP-AESGFAASFAAS Detection LimitsExcellentGoodExcellentGood ProductivityExcellent LowGood Precision1-3%0.3 – 2 %1 – 5 %0.1 – 1 % Chemical Interferences ModerateFewMany IonizationMinimal Some Mass EffectsHigh on low mass None Dissolved solids0.1 – 0.4 %2 – 25 %Up to 20 %0.5 – 3 % # Elements Sample UsageLowMediumVery LowHigh Isotope AnalysisYesNo Method DevelopmentSkill required Easy Running CostsHigh MediumLow Capital CostsVery highHighMediumLow

ICP-MS Components Sample Introduction Plasma Generation Interface Ion Optics Mass Analyzer Vacuum System

Sample Introduction Delivers finely divided sample (usually aerosol) to plasma Plasma Source  Ion Source  Ar plasma  K Interface Allows transfer of atmospheric pressure ion source to high-vacuum mass analyser

Ion Optics Focuses ion beam and helps eliminate neutral species and photons Mass Analyzer Separates and measures individual ions by mass Vacuum System  Provides low pressure environment for mass spectrometer to operate effectively (no collisional losses)  Enables transition from plasma to high-vacuum via interface region

The Detector Converts ions into electrical pulses Magnitude of the electrical pulse is proportional to the number of ions in sample

Sample nebulized in spraychamber Argon transports sample and sustains plasma RF generator supplies energy to induction coil Sample atomized and ionized in the plasma Ions are transmitted through the interface, most of the gas removed Quadrupole filters the ions by mass Detector counts the ions Steps Involved in ICP-MS

How is a Plasma formed?

Sample Introduction System Low uptake concentric nebulizer standard External spraychamber  Double pass glass spray chamber  Room temperature to -15º C  Moves with torch Three channel peristaltic pump  Computer controlled  Smart Rinse enabled for optimized rinseout

The Plasma A plasma is a cloud of ionized gas Plasma temperature K Most elements >90% ionized Singly charged positive ions predominate Small molecular and doubly charged ion population Complete elemental analysis in a single determination

ICP-MS Torch

Process to form Plasma A flow of argon gas is passed between outer and middle tube of torch RF power is applied to load coil producing intense electromagnetic field A high-voltage spark produces free electrons Free electrons are accelerated by electric field Accelerated free electrons produce high energy collision and ionization of Argon gas Self-sustaining plasma is formed at open end of quartz torch

Processes in the Plasma Recombination ← Ionisation ← Atomisation ← Vaporisation Oxides ← Ions ← Atoms ← Gas ← Solid ← Liquid Sample aerosol M(H 2 0) + X- MXn MX M+ MO+

ICP: Why are there four gas flows? – Auxiliary Flow holds plasma away from torch/injector tube prevents torch melting – Plasma Flow forms the plasma – Nebulizer Flow punches cooler channel through centre of plasma carries sample – Sheath Gas (some ICPMS instruments) Allows control of the velocity of the center channel independent of the sample delivery rate

Interface: Ion Sampling TURBO- MOLECULAR PUMP VACUUM PUMP SAMPLER CONE SKIMMER CONE PLASMA ZONE OF SILENCE INTERFACE ~5 Torr ATMOSPHERE 760 Torr ROTARY ION OPTICS ~1x10 -4 Torr

19 ICP-MS Cones Sample Ions from the Plasma Sampler Cone Plasma encounters this cone first Skimmer Cone Located behind the sampler cone

The Mass Spectrometer Responsible for the high sensitivity of ICPMS instruments. Separates ionized species on the basis of their mass to charge ratio. Requires high vacuum (~ Torr) to operate Resolution must allow detection of low concentration elements in presence of adjacent high concentration elements. Scanning speed must be fast enough to cope with transient signals from various sample introduction systems Must accept a wide distribution of ion energies

Mass Spectrometer: Common Mass Analyzers Quadrupole Ion Trap Time of Flight Double-Focusing Magnetic Sector

Mass Spectrometer: Quadrupole Mass Analyser Schematic Only one mass has a stable trajectory

Vacuum System: Turbomolecular Pumps

Rotary Pumps

Element Name Element Symbol ArsenicAsLithiumLi BariumBaManganeseMn BerylliumBeMercuryHg BismuthBiNickelNi CadmiumCdRubidiumRb CesiumCsSeleniumSe ChromiumCrSilverAg CobaltCoStrontiumSr CopperCuThalliumTl GalliumGaUraniumU IndiumInVanadiumV LeadPbZincZn Elements analysed by ICP-MS in ARD

Analysis of Samples by ICP-MS Follow BCSIR SOP – 22 Prepare tuning solution Prepare standard solution of metals of different concentrations Always use de-ionized water having a resistivity of 17.5–18.5 MΩ/cm Use suprapure ICP-MS grade acids

Seven Elements of Quality Control during sample analysis by ICP-MS Certification of operator competence Calibration Analysis of externally supplied standards Analysis of blanks Analysis of duplicates Recovery of known additions Control charts

The End