The signal response of a chromatogram is directly related to volume of sample injected. In case the chromatographic peak shapes are ideal then peak height is considered otherwise the area count of the peak is in proportion to the sample volume injected. The two modes available for sample injection are manual injection or automated injection using the autosampler.
Advantages of Automated Injection
Automated injection offers several advantages which contribute to high accuracy and reproducibility of results.
Manual injection is prone to personal errors whereas automated injection delivers a constant volume every time. The injected volume can be changed as per user instructions.
The analyst can decide the number of repeat injections in order to get highest reproducibility of results.
Mix up is avoided as the vials are sealed and placed in known positions of autosampler tray. As programmed the autosampler arm selects in sequence from respective vial positions. This eliminates manual errors that an operator is likely to make.
The injection sequence can be set as per the analyst program. In case there is a change of priority the autosampler sequence can be interrupted to accommodate the desired change.
In between the sample analysis the autosampler syringe and needle can be programmed to carry out the required number of wash cycles using the blank. The number of required wash cycles can be varied depending upon the sample to sample requirements.
Injection of Standards
The analyst can place a standard solution in a vial and standard injections can be made after every 3 to 4 sample injections. This helps monitor the operating condition of the column.
Analysis of Large Number of Samples
Autosampler trays can accommodate around hundred vials. This is a big advantage as the analyst can load the number of samples as per analysis requirement in a single step.
The biggest advantage of automated injections is saving of time. The analyst after preparing the series of samples and standards simply loads the vials inside the autosampler tray and is free to attend to other tasks. The availability of extra time results in higher laboratory throughputs in terms of samples analysed.
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