Chromatography Forum

Just curious on how people have handled configuration of multiple detectors on an 1100 system. Right now I have a DAD, Fluorescence, and a RI detector. The main hplc stack has the DAD at the bottom of the stack, and the Fluorescence and RI are stacked next to the main HPLC system. I'm considering either running in series, DAD --> Fluorescence --> RI, or using a t and running the DAD and Fluorescence in series, and the RI in parallel. Other option is just hooking up the DAD and switching it out with the other 2 detectors as needed. Curious as to how others handle similar setups. Analysis ranges from peptides, beverages, cosmetics, nutritional supplements, etc.

In a lab where we had DAD and Fl, we would keep them in the stack in that order. Part of that was because we wouldn't always use the fluorescence detection, but always used DAD/UVD. These would be kept on one stack. With adding RI, or ELSD or any third or fourth detector we would pull the detectors into their own stack right next to the LC Separations stack. This would also allow us to more easily switch between single detectors.

In all honesty, it was overkill. We kept the DAD hooked up first since it was always used for analysis. ELSD was almost never connected in the flow path. RI was sometimes hooked up, but always last. Hope this helps you.

In order to make a productive suggestion, we would first have to know how often you require one or more of the detectors when you perform routine analysis? Need will justify what the most logical approach will be. For most users who have multiple detectors available, a full scanning DAD will always be in the first position (The UV/VIS DAD is the most useful detector of all). If regularly used, Florescence (FLD) would be connected IN-SERIES next (be very careful to not plug or obstruct the lines or flow cell of the FLD, or any other detector). Finally, if RID is needed, it should always be connected in series, after the DAD, never in parallel (you would loose so much signal doing that, plus it would add variability and broadening). Ideally, only connect the detector(s) needed for the specific method, in-line, for the analysis method.

If you do not use the FLD or RID often, you may be better off having only the DAD in-line as default, then use a high quality, one piece Fingertight connector to make any needed connections to place either the FLD or RID in series with it, only when needed.
As noted, the scanning DAD, if correctly plumbed using short, narrow tubing from the column outlet is the most useful AND should always be first in-line.

While it is possible to install diverter valves to "select" the needed detector, we do not recommend this option. Doing so adds too much complexity for most users (they forget to switch the correct detectors inline AND forget to document it for GLP requirements, failing validation).

Yes, the DAD can be the module at the bottom of the stack, with the other two detectors stacked next to it so the connection can be short). That is how we install them when performing an install for clients (Side-by-Side stack offers the best utility. It allows most users to safely reach the solvent bottles while keeping the connections between modules as short as possible for the best chromatography).

I'm in agreement with what Multidimensional posted.

When I was working, we oftentimes changed set-up of our "stacks" to accommodate refractive index, ELSD, conductivity detectors as needed. Most times I used PEEK tubing and fingertight fittings.

Changing detectors should be a very minor task for an experienced chromatographer.

It is possible to run that in sequence as long as FLD used at last detector, which means DAD---> RID ---> FLD or RID ---> DAD ---> FLD. It is just because of that the excitation light may destroy the structure of the components/analysts. however, the DAD or RID unlikely damage the components.

Just curious on how people have handled configuration of multiple detectors on an 1100 system. Right now I have a DAD, Fluorescence, and a RI detector. The main hplc stack has the DAD at the bottom of the stack, and the Fluorescence and RI are stacked next to the main HPLC system. I'm considering either running in series, DAD --> Fluorescence --> RI, or using a t and running the DAD and Fluorescence in series, and the RI in parallel. Other option is just hooking up the DAD and switching it out with the other 2 detectors as needed. Curious as to how others handle similar setups. Analysis ranges from peptides, beverages, cosmetics, nutritional supplements, etc.

The pressure rating of the flow cells must be considered at the first place.
FLD has the most sensitive cell according to my knowledge , and RID is the second.
The outlet tubing of those cells are wider than standard tubings , may be 0.5 mm ID , so may cause peak dispersion , if connected at the first position.

Not agree with the excitation light of FLD destroys the structure of components , it is a monochromatic light , but DAD may do it , all the spectrum of UV light passes through the flow cell first, then the monochromator sends the passing UV light to diode array.