next up previous contents
Next: 5. General Mass Spectrometry Up: 4.3 Sample Introduction Into Previous: 4.3.2 Other Inlet Techniques   Contents

4.3.3 Manual Injection vs. Automatic Injection

Several methods exist for manual injection that utilize different syringe insertion speeds, thermal equilibration times, plunger speeds, etc. Injection volumes tend to be less precise with manual injection; however, this is of very limited importance since any quantitative analysis we do is by the internal standard method. Retention times are also less precise with manual injection, but unless the operator is very inexperienced, this is not enough to be of practical importance.

An autosampler allows automated (and relatively reproducible, in both injection volume and retention time) injection and syringe cleaning. The sampler is programmed for operation, such as the number of wash cycles, the sample bottle to use, the amount to inject, etc. The use of an autosampler also allows batch or sequence running, which essentially frees the analyst to do other things while the instrument executes many runs.

John S. Riley, DSB Scientific Consulting