Smaller Injection Volumes

The Thermo Scientific UltiMate 3000 WPS-3000RS Well Plate Autosampler is a high performance instrument for HPLC and UHPLC. It is highly accurate and precise and provides high injection volume flexibility with excellent linearity performance at pressures up to 1034 bar. This is demonstrated in the following linearity plots covering injection volumes of 1 µL – 10 µL and 10 µL – 100 µL.

Excellent linearity performance at 1 µL – 10 µL in 1 µL steps  (correlation coefficient of 0.999997,  three replicates per level) and 10 µL – 100 µL (correlation coefficient of 0.999998, three replicates per level) demonstrate the flexibility of the WPS-3000RS Rapid Separation Autosampler.

UHPLC gives faster chromatography on columns with smaller volume. In order not to overload these columns, smaller injection volumes are required. So an interesting point to look at is the performance of the WPS-3000RS Well Plate Autosampler in the sub-1 µL range.

In our test scenario we have injected a standard of uracil, dimethylphtalate and phenanthrene in the range of 0.2 µL – 1 µL in steps of 0.1 µL and separated these analytes within 10 min in a 70/30 acetonitrile/water isocratic HPLC run. The concentration of the standard was chosen so that a signal-to-noise value for phenanthrene of 90 was achieved.

The draw speed was set to 0.5 µL/s and thus the sample was aspirated within 2 s (1-µL injection). We also tested a sample aspiration time below 2 s, but found that peak area RSD values increased slightly. The draw delay was set to 3 s (default value). The wash/sample push solvent used in these runs was 60 % acetonitrile in water and was on-line degassed.

As shown in the following plot we obtained excellent linearity data within the injection volume range of 0.2 to 1 µL. The peak area precision obtained for the 0.6-µL injection was 0.55% and 0.35% for Dimethylphtalate and Phenanthrene (N = 3) respectively.

Linearity data at 0.2 µL – 1 µL in 0.1 µL steps (three replicates per level; Dimethylphtalate: correlation coefficient of 0.99986; Phenanthrene: correlation coefficient of 0.99992) demonstrate the excellent injection linearity performance of the WPS-3000RS Rapid Separation Autosampler in the sub-1-µL range.

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