ELS detector for high-speed separations

[XL]

Waters has AcQuity UPLC evaporative light scattering (ELS) detector.
Agilent has 1200 ELS detector (OEM from Sedere Sedex-85 LT
There are also other ELS detector manufacturers.

My question: which ELS detector is best suited for high-speed separations (say peak width < 1s)? Any references, examples, sharing of firsthand experience, and comments are appreciated?

[XL]

I must have asked a wrong question since there has been no response for 48 h. I am wondering probably not many chromatographers use an ELS detector for ultra fast analysis. Any comments?

[AA]

The ACQUITY ELS was designed for narrow peak widths, although we seldom get below 1 second. It will collect data at 80 Hz which is more than fast enough (40 Hz is more than fast enough for a 1 second peak). It is the nature of this detection technology (from any vendor) to add peak width as the peak passes throug the drift tube. If I remember correctly, some studies I did showed about a 15% increase in peak width compared to the same assay done with UV.

Fast chromatography using ELS is widly done, often as part of multiple detector (UV/MS/ELS/ sometimes CLND) configurations in drug discovery labs.

I have never used the sedex for fast LC so I can't comment on it.

AA

[Kostas Petritis]

I know that SEDERE has worked a lot in optimizing their ELSD nebulizer, evaporative tube etc for micro and UPLC applications. They have worked in part with Jean-Luc Veuthey in Switzerland on that matter (part of it applications). I think that data rates can go up to 100 Hz. You can have a look at this application for some UPLC work done with the SEDERE detector.

J. Sep. Sci. 2008, 31, 2377 – 238

[XL]

Thanks, AA and Kostas, for the comments and information.

Peak width depends on the design of the ELS detector (low dispersion) and to a lesser extent, data collection rate. Since 40 Hz is more than adequate for an ELS detector, why higher data collection rates are still adopted by ELS detector manufacturers? Are there any compromises when using higher data collection rate? It seems everything comes at a cost.

[AA]

What I said was for a 1 sec wide peak, 40 Hz is high enough. Also peak width is primarily influenced on what is happening prior to the detector, system volume, flow rate, column i.d., column packing diameter,post column dispersion, chromatographic behavior of the compounds, and other stuff too. Certainly, detectors (any detector) can, and do add some peak width physically and electronicly (data rate and filter constant can appear to add very large amounts of peak width if chosen poorly).

Why do instrument vendors have higher than needed data rates? 1: Planning for the future, a detector lifespan should be many years, who knows how low peak widths will go, if you manage to generate a 0.25 sec peak, then you will need 80 Hz or higher. 2:Competitive advantage, some customers sometimes think in very simple terms, i.e. faster is better, so having the system with the highest data rate can sometimes give a slight competitive advanatge.

And yes there are compromises at higher data rates, mainly higher baseline noise.

[AnalyticalKen]

I'm late posting to this topic, but I do have a lot of experience with using ELSD in connection with fast chromatography. I have performed extensive evaluations on the Sedex/Agilent, Softa, and PolymerLabs units. There are differences between the units. Here are some general observations.
1. Peak widths will be wider for ELSD than for UV. This is a function of what happens in the liquid to gas transition.
2. If you are talking about 1 second wide peaks at half height, that can be achieved with the appropriate instrument.
3. If you are talking about 1 second wide peaks at the base, that is achievable, but very difficult.

I will say that we use the Softa units in our lab. If you are interested in knowing more, give me a call 919-323-4299 and I can tell you about my experience and send you some of the comparision data.

Good Luck,
Ken