Agilent Technologies has produced a Technical Overview demonstrating the injection principle used in the Agilent 1260 Infinity II SFC Multisampler. In this instrument, the sample volume is drawn under atmospheric pressure conditions, pressurized to system pressure, and injected by an ultrafast syringing process. Data are presented that the 1260 Infinity II SFC Multisampler enables the injection of flexible sample volumes with highest precision, and excellent linearity over a broad volume range.
In contrast to the variable sample introduction of classical HPLC instruments, where the mobile phase filled sampling path can harmlessly experience atmospheric pressure, SFC instruments must avoid using mobile phase at ambient pressure in sampling paths to prevent evaporation of the dense CO2. Evaporation of the CO2 in the sampling path could lead to either a complete loss of the sample or an incomplete injection. Therefore, the fixed loop approach, where a previously filled loop was switched into the pressurized CO2 stream, has been the method of choice for SFC. While this approach yields good peak area precision for full loop injections, it requires loop overfilling and hence a waste of sample. When used for partial loop filling, it requires complicated implementations, and compromises precision performance.
The 1260 Infinity II SFC Multisampler enables the injection of flexible sample volumes with the highest precision, in contrast to the widely used fixed-loop approach discussed above. In the 1260 Infinity II SFC Multisampler, the sample volume is drawn under atmospheric pressure conditions, and pressurized to system pressure before it is injected into the analytical flow path by an ultrafast syringing process.
Results and Discussion
The fixed-loop approach is used for sample injection in SFC instruments as a state-of-the-art technique. This approach enables the injection of fixed volumes with high precision, but volumes that are injected by a partial loop fill suffer from compromised precision. The variable-loop concept that is widely used for sample injection in HPLC instruments cannot be used because liquid CO2 cannot be subjected to atmospheric pressure. This would lead to partial or complete loss of the sample due to evaporation. To overcome this drawback, a flexible injection principle was introduced with the 1260 Infinity II SFC Multisampler for the Agilent 1260 Infinity II Analytical SFC solution.
This Technical Overview demostrates how variable injection volumes at the highest precision can be achieved using the the Agilent 1260 Infinity II SFC Multisampler. The area RSDs for injection volumes between 0.5 and 10 μL are typically below 0.3 %. Even lower injection volumes, down to 0.1 μL, showed area RSDs typically below 2.5 %. The demonstrated injection linearity is typically better than 0.9995. Even for injection volumes of up to 80 μL, excellent area RSD values below 0.3 % could be achieved. The linearity of the peak area for large injection values is also extremely good.