( Chromatography and Mass Spect...)Accurate Evaluation of the Finnigan Surveyor Autosampler Performance using a Deferred Standard

Chromatography and Mass Spectrometry Application Note

Diab Elmashni and Andre Nohl Ph.D,
Thermo Electron Corporation, San Jose, CA, USA

Introduction
The Deferred Standard (DS) concept was introduced more than 40 years ago with the purpose of monitoring the reliability of process chromatography. The DS consists of an injection of a pure compound during a chromatographic run. The DS injection is deferred from the sample injection. The delay between the sample injection and DS injection is under the users control. This allows positioning the DS peak in any convenient location within the chromatogram. The DS can be thought of as a cross between an internal and external standard. The selection of a DS compound is easy because its elution time is controlled through the injection delay. Any compound compatible with the separation method can be used as long as it can be obtained as pure compound. A good choice may be one of the sample compounds, if available with sufficient purity.

The DS being a separate injection of a pure compound can be used to independently evaluate the reliability and reproducibility of a chromatographic system. Because the DS elutes during sample chromatographic runs, it allows validation of the current run and the analytical result. In the case of autosampler evaluation, the DS allows for the isolation of the error contribution of the autosampler from the total system error. The DS is injected by a separate sampling system whose precision is known to be excellent (full loop injection) and reliable. The DS peak area is used to measure the precision of the HPLC system (pump, column, detector, data collection system) with the exclusion of the autosampler. Analyzing the results from the sample and the DS gives a direct measure of the autosampler reproducibility and guarantees that uncertainties from the rest of the HPLC system are not wrongly attrib
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