LALI-TOF-MS – An Alternative to ICP-MS/ICP-OES

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a well-known and popular analytical technique used to determine the elemental composition of a sample with trace and ultra-trace level sensitivity. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) is a very similar technique that uses a different detection technology with slightly less sensitivity.

How Does ICP-MS/ICP-OES Work

Both techniques only work on liquid samples, hence, solid samples must be converted via acid digestion.

The liquid is then introduced to a high-temperature argon plasma as an aerosol via a nebuliser. The plasma ionises material which is then analysed by a mass spectrometer (for ICP-MS) or optical emission spectrometer (for ICP-OES) that that measures the wavelength of light emitted by the excited atoms in the plasma.

The use of ICP techniques is well-established and accepted in many industries.

How Does LALI-TOF-MS Work?

Laser Ablation Laser Ionisation Tome-of-Flight Mass Spectrometers ( LALI-TOF-MS) use a laser to ablate the surface of a solid sample, requiring virtually no sample preparation for solid samples. A second laser ionises the ablated material that is then extracted and measured using a time of flight mass spectrometer. More details at www.axt.com.au/lali-tof-ms-principles-capabilities.

Comparison

	ICP-OES/ICP-MS	LALI-TOF-MS
Sample Preparation	Acid digestion, dilution & chemical processing	Virtually none
Sensitivity	Typically ppt	Typically ppb
Measurement speed	Long	Short
Isotopic analysis	No/Yes	Yes
Mapping	No	Yes
Depth profiling	No	Yes
Consumable requirements	Ultra high purity Argon gas, acid and plasticware	None
Relative operating costs	High	Low
Maintenance	Frequent tuning, cleaning and gas supply maintenance	Minimal
Carbon footprint to operate	High	Low
Operator expertise required	High	Low
Instrument size	Large	Compact
Infrastructure requirements	Temperature & humidity controlled lab capable of up to 10000BTU/hr, fume hood with exhaust ducting, 240V power supply	Standard temperature & humidity controlled lab, standard 240V power supply
Space requirements	Approx 2.5m of bench space for instrument, autosampler, computer and clearance, plus sample prep and chiller	600 mm of bench space
Sample disposal	Complex	Easy

Detection Limits

The following graphic compares the sensitivity of LALI-TOF-MS with other elemental analysis techniques such as LA-ICP-MS (which has similar sensitivity to ICP-MS), XRF and LIBS.

Running Costs

This is based on:

1,000 hours / year
Electricity, Gases, and Consumables*
Half a year’s salary for Operator:
ICP-OES: Senior-level technician
ICP-MS: Doctor of Philosophy (PhD)
LALI: Technician

Workflow Comparison

The ICP-MS workflow is quite extensive and labour-intensive in comparison to LALI-TOF-MS which is both simple and quick.

	LALI-TOF-MS	ICP-MS
Sample Prep. Time	2min	Full day
Sample Prep. Requirements	– Carbon-backed tape – Lab technician	– Clean room – Nitric or HF acid – Microwave digester Ultra-pure water – Trained experts
Calibration Time	10 min	Full day
Calibration Requirements	– Reusable reference materials – Single-point calibration – Lab technician	– Standard solutions prepared for each analysis – Spectral interference corrections – Multi-point calibration curve – PhD chemist

Summary

LALI-TOF-MS and ICP-MS / ICP-OES are all techniques for determining the elemental composition of material. While ICP-MS offers slightly better limits of detection compared to LALI-TOF-MS the workflow is much more involved (in particular sample preparation and calibration) and it requires a more highly trained operator, especially for solid samples which require acid digestion. LALI-TOF-MS on the other hand is fast, simple, requires virtually no sample preparation for solid samples. Furrthermore, it can be performed by a technician and has minimal infrastructure requirements, making ideal when ICP-MS detection limits are not required or rapid analysis is needed.

LALI-TOF-MS is commercially available from Exum Instruments in the form of the Massbox which features a user-friendly, intuitive interface to streamline the measurement process.