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Sample Introduction Systems

ample Introduction

The most common form of ICP sample introduction is liquid. The purpose of this section is to introduce the beginner to the

most popular components of liquid sample introduction systems used for the introduction of samples to ICP-OES and ICP-

MS instrumentation (hereafter referred to as ICP) and to alert the reader to some common problems.

System Components

Before continuing any further, I strongly encourage you to read the following: A Beginner's Guide to ICP-MS Part II: The

Sample-Introduction System*

In the above article, author Robert Thomas gives an excellent overview of the most popular commercially available nebulizers

and spray chambers. He also provides guidance and basic theory behind the available designs, as well as an overall

understanding of ICP introduction systems.

The key elements of a sample introduction system start with the sipper tube and end with the torch. They are listed as follows:

1. Sipper (typically plastic)

2. Teflon tubing going from the sipper to the peristaltic pump tubing

3. Peristaltic pump tubing

4. Teflon tubing going from the peristaltic pump tubing to the nebulizer

5. Spray chamber

6. Torch

Troubleshooting

Connection Checks

The main difficulty I have experienced with introduction system failure is that of connections between components. The

connections are listed as follows:

1. Sipper to Teflon tubing

2. Teflon tubing to peristaltic tubing (both into and out of)

3. Teflon tubing from peristaltic pump to nebulizer

4. Nebulizer to spray chamber

5. Spray chamber to waste drain tube

6. Spray chamber to torch

If any one of these connections is not airtight, the operator will experience anything from poor precision to an inability to

light the plasma. One of the many reasons I prefer concentric glass nebulizers is that they are ‘free flow’ (i.e., the liquid will

flow from the sample container to the nebulizer without assistance from the peristaltic pump). A simple check is to determine

if you obtain a fine steady mist (using water as the sample) without the peristaltic pump (pressure lever released) so that free

flow can occur. This can be done with the nebulizer disconnected from the spray chamber (plasma has not yet been lit) so that

the mist can be easily visualized. You can also check for the appearance of any small air bubbles in the Teflon tubing, which

should never be present and indicate a poor connection somewhere between and/or including the sipper and the nebulizer.

Another connection that is often taken for granted is the spray chamber drain/waste tube connection. This connection

is absolutely critical. One way to test this connection is to put some water in the spray chamber using a wash bottle and

determine if it drains smoothly and without leaks. Poor precision or the inability to light the plasma is a common symptom

of a poor drain tube connection. During this test you should also observe the absence of water droplets in the spray chamber

(assuming glass construction). A dirty spray chamber will leave water droplets and cause poor precision and carryover

problems. Make sure the plasma is not lit whenever you perform this test.

Spray Chambers

Spray chambers can be made of all glass, all plastic, and glass with plastic end caps. If you do not use HF (all plastic systems

must be used with HF) and therefore have the luxury of using glass components, attempt to use a spray chamber without