Chromatography Forum

What are the slit (nm) and peakwidth (s) functions on the Agilent 1100 DAD adjusting when they are changed. Also how do these changes effect the chromatogram. I am running Empower2 software. I thought slit was only employed when not using a diode array so it might be a function that is only active when using a different detector and empower2 software. Thanks.

The slit width is called that by analogy with spectrophotometers, where the width of a physical slit can be changed to alter the bandpass (narrow slit = better spectreal resolution but more noise; wider slit = worse spectral resolution but less noise). In the case of the DAD, what is actually happening is that signals from neighboring diodes are combined.

I wasn't aware that there was a "peak width" function in the DAD itself. That term is mostly used in a data system to screen out high-frequency noise and drift.

One of the problems with all of these terms is that there is no standardized terminology, so that different vendors use different terms for the same function (and often different functions will have similar names).

In a recent thread, I noted that the 1100 DAD manual discusses the "slit", which is a physical component of the DAD.... The spectrograph consists of "...the lens, the variable entrance slit, the grating, and the photodiode array with front end electronics"

The variable entrance slit system is further defined - apologies for the blatant Agilent self-promoting gobbledygook.

" The micro slit system makes use of the mechanical properties of silicon combined with the precise structuring capabilities of bulk micro-machining. It combines the required optical functions - slit and shutter - in a simple and compact compartment. The slit system is directly controlled by the microprocessor and can be set as a method parameter."

Setting the slit to 1,2,4,8, and 16 nm is possible, and 4 is typical. Slit setting should not exceed signal bandwidth setting.

I assume the electronic accumulation of individual diode outputs is the bandwidth, and is set according to the sample's absorbance band.

Confused yet?

Bruce, thanks for clarifying that. I was fixated on the exit slit and forgot the fact that even a DAD has a physical entrance slit!

But if anyone has an English translation of that technical description, I'd be most interested.

The "peak width" setting occurs on all Agilent detector modules. It is Agilent's way to set the data acquisition rate. You should set this value to match the peak width at half height of your most narrow peak. If this value is larger than the actual peak width, your observed peak can be distorted.

Note: I am assuming that Empower is using these values in the same way that Agilent does.