Criteria, detector performance

The performance of all HPLC detectors can be characterised by certain parameters such as sensitivity, noise, drift, limit of detection, linear and dynamic range, and detection volume. Other factors are more specific to individual types of detectors, and are discussed in their respective sections. 

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Another aspect of cost reduction would be solvent economy. The need to preferentially select inexpensive solvents and employ the minimum amount of solvent per analysis would be the third performance criteria. Finally, to conserve sample and to have the capability of determining trace contaminants, the fourth criterion would be that the combination of column and detector should provide the maximum possible mass sensitivity and, thus, the minimum amount of sample. The performance criteria are summarized in Table 1. Certain operating limits are inherent in any analytical instrument and these limits will vary with the purpose for which the instrument was designed. For example, the preparative chromatograph will have very different operating characteristics from those of the analytical chromatograph. 

Many laboratories have a criterion of performance based on the percent chemical yield. The recovery, for example, may have to exceed 50% to meet this criterion. The radiochemical yield is the fractional recovery of the amount of added tracer. Its measurement requires that the counter efficiency (e) is known (see Experiment 6). The counting efficiency can have been determined in a previous experiment and recorded with the detector information. 

Autosampler precision can be checked by replicate injections of a control sample, with wash injection intervals between every two sample injections. The repeatability of peak areas, mathematically expressed as RSD, is used as a criterion for autosampler precision. For example, when 10 consecutive injections of 10 pL of a solution are performed, the expected RSD for peak area precision ranges from 0.5% to 1.0%. Single injections of different volumes, such as 5, 10, 50, or 80 pL, can also be used, simultaneously checking the linearity of the injector, the detector, and the data system. Another approach to qualify the autosampler involves the gravimetric determination of the average volume of water per injection withdrawn from a tared vial after six 50-pL injections. The procedure... 

However, the measurement specificity is yet another important consideration in assuring the desired results conventional GC detectors can hardly satisfy this criterion if the measurements are performed in crude biological extracts. In this view, it is hardly surprising to read the statement by Adlercreutz and Luukkainen... 

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