Sample Introduction

What is sample introduction?

Sample introduction describes the overall strategy used to deliver an analyte to the ion source.

There is no single sample-introduction method suitable for every type of mass spectrometry.

The method depends on:

• physical state of the sample

• analyte concentration

• volatility

• thermal stability

• complexity of the mixture

• required sensitivity

• need for separation

• ionisation technique

LC–MS

For LC–MS:

Sample vial → autosampler → injection valve → LC column → MS source

Advantages include chromatographic separation and compatibility with many polar and non-volatile compounds.

GC–MS

For GC–MS:

Sample → GC inlet → vaporisation → GC column → transfer line → MS source

It is primarily suited to compounds that are sufficiently volatile and thermally stable, either naturally or after derivatisation.

Direct infusion

For direct infusion:

Sample → syringe pump → emitter → ion source

This provides continuous introduction without chromatography.

It is particularly useful for standards, source optimisation and controlled MS/MS experiments.

Flow injection

Flow injection introduces a sample into a flowing solvent stream without chromatographic separation.

It sits conceptually between direct infusion and LC separation.

Other introduction techniques

Depending on the scope of your portal, learners can later encounter methods such as:

MALDI: sample is co-crystallised with a matrix on a target plate and irradiated with a laser.

Headspace GC: volatile compounds in the gas above a sample are introduced into a GC.

SPME: analytes are extracted onto a coated fibre before introduction into a GC.

DESI and other ambient techniques: samples can be analysed directly from surfaces with minimal preparation.

Choosing an introduction method

A useful conceptual comparison is:

The complete sample journey

This page is a good place to bring the entire Sample Handling module together:

1. Sample preparation

The analyte is extracted, diluted, filtered or otherwise prepared.

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2. Sample storage

The prepared sample is placed in a vial, plate, syringe or other container.

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3. Sample selection

An autosampler or operator selects the sample.

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4. Injection/introduction

A defined quantity enters the analytical system.

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5. Transport or separation

LC, GC, capillaries, pumps and valves control where the sample travels.

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6. Interface

The sample reaches the interface between the separation system and MS.

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7. Nebulisation/vaporisation

Where required, the sample is converted into droplets or gas.

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8. Ionisation

Neutral analyte molecules are converted into gas-phase ions.

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9. Ion transfer

Ions enter the mass spectrometer.

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10. Mass analysis and detection

The instrument separates ions according to \(m/z\) and records their abundance.

Key takeaway

Sample introduction is the bridge between the physical sample and the production of ions that can be measured by the mass spectrometer.