Agilent 1100 Series diode-array detector SL for optimization of speed, resolution, sensitivity, and spectral performance in Ultra-fast LC
by Angelika Gratzfeld-Huesgen, Michael Frank and Stefan Schuette, Agilent Technologies, Waldbronn, Germany
Increasing productivity while maintaining or improving data quality and security is one of the most important objectives of today's analytical laboratories. To meet this challenging objective Agilent has continuously developed its 1100 Series LC system and ZORBAX columns over the past decade. This has resulted in significant improvements in technology and opened up the new field of Ultra-fast LC, which facilitates injection-to-injection cycle times of less than 1 minute, analysis times less than 30 seconds and peak widths smaller than 1 second. To date this level of performance has only been achievable through the combination of four major elements:
•Binary pumps with high-pressure mixing for precise formation of high-pressure gradients
•High-speed well or vial plate autosamplers with flow-through design, 6 μL delay volume and overlapped injections for precise low carryover injection cycles faster than 30 seconds
•Peltier-controlled column oven with 2-position, 10-port valve for automated alternating column regeneration for reduced column wash and regeneration times
•Short rapi-resolution high throughput columns with 1.8 μm particles for increased throughput and flow rate independent efficiency
However, current diode-array UV detectors with 20 Hz signal sampling rate and 10 Hz spectral rate are simply not fast enough to accurately measure chromatographic peaks narrower than 1 second as delivered by ultra-fast LC. To overcome this limitation Agilent has introduced the 1100 Series DAD SL with 80 Hz multi-signal
and full spectral sampling rate for identification, quantitation and spectral analysis of peaks as narrow as 0.2 seconds.
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Figure 1: Influence of data rate on chromatographic resolution. |
Optimization of data rate for highest resolution in ultra-fast LCThe application example shown in Figure 1 and the related Table 1 demonstrate how significant detector data rate and corresponding response time influence chromatographic performance of an ultra-fast separation. In the given example the true peak width measured with 80 Hz data rate and a detector response time of 0.05 sec is about 0.3 sec at half height. When the data rate is decreased to 20 Hz, the increased response time causes a 40% increased peak width of 0.42 sec. At the same time peak capacity and resolution are decreased by 40% and 30%, respectively. In terms of apparent column efficiency the loss is 70%. Compared to the maximum possible spectral rate of 10 Hz the performance loss is even more significant. At 10 Hz data rate the peak width increases by 120% to 0.67 sec. This causes 120% loss is peak capacity, 90% loss in resolution and 260% loss of apparent column efficiency. In other words, the resolution gain achieved by 80 Hz data rate equals a virtual increase in column length by a factor of 2.6.
Data Rate | Peak Width | Resolution | Peak Capacity | | 0.300 | 2.25 | 61 | 40 Hz | 0.329 | 2.05 | 56 | 20 Hz | 0.416 | 1.71 | 55 | 10 Hz | 0.666 | 1.17 | 28 | 5 Hz | 1.236 | 0.67 | 16 |
Table 1: Influence of data rate on peak width, resolution and peak capacity. |
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Figure 2: Signal-to-noise determinations of low-level impurities measured at 80 Hz. |
Dynamic Range — Sensitivity and Linearity in ultra-fast LCThe upper linearity limit of UV detectors is not affected by increasing the data rates. Short-term noise, however, increases proportional to the square root of the increase in data rate, thereby reducing the dynamic range. To compensate this effect short-term noise and practical noise under gradient conditions has been improved on the 1100 DAD SL such that the detector delivers the same dynamic range under ultra-fast LC conditions as former diode-array detectors under conventional conditions. Figure 2 shows that the DAD SL allows simultaneous quantitation of main compounds and impurities measured at 80 Hz data rate at levels of less than 0.05% (1 mAU).
The complete note (publication number 5989-3070EN) can be downloaded at www.agilent.com/chem/DAD-SL
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