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Comments
A
Rheodyne front-loading injector, properly operated, can inject volumes
onto the column with the following precision: 1) Using the partial-filling
technique, 0.2% to 2% RSD, depending on operator skill at setting the
syringe plunger reproducibly. 2) Using the complete-filling technique,
0.05% to 1%, depending on the volume loaded relative to the volume of
the loop. Loading excess sample of five loop volumes produces about 0.1%
RSD. See Appendix E. The observed precision of
peak heights and areas depends also on the stability of flow rate, mobile
phase composition, and column temperature, and therefore the RSD is usually
larger.
Accuracy is the closeness of an injection to the specified sample volume. A front-loading injector can inject volumes with the following accuracy: 1) Using partial-filling, 1% to 2%, depending on the syringe and operator skill. 2) Using complete- filling, 5% to 30%, depending on the loop. This is because loop size designations are nominal. Actual volumes differ because the tubing bore has a 0.001 in tolerance. Accuracy of large loops (2 mL) is about 5%, intermediate loops (20 µL) 10%, and small loops (5 µL) 30%. To find the actual injected volume, calibrate the loop, while attached, to take into account the injector's internal passages.
Non-reproducible Results
The following pages discuss the problem of poor analytical precision, i.e., the variation in peak height and peak area. The injector cannot affect retention time, except for the very unlikely event of an erratically fluctuating leak that causes variable flow rate in the column.This section also discusses the problem of a change in peak shape.
When troubleshooting, be aware that there are many causes for non-reproducible results other than the injector.
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