Can I get some advice choosing an HPLC?

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

8 posts Page 1 of 1
I'm charged with choosing a new HPLC system for my company. We currently have several established methods that we run on our HPLCs, but we'll be looking to do method development in the future. My questions are:
    1) Which HPLC systems (for those who've purchased in the past 5 or so years) are recommended? We're looking at Jasco, Agilent, and Thermo. We're leaning towards Agilent because of customer aftercare, but robust instrumentation is also important.
    2) I'd like to get a DAD detector over a regular UV detector. Stupid question, but a DAD can be ran at only one wavelength as opposed to many correct? Also, how is the sensitivity of newer DAD compared to UV detectors? We have a method (our method requiring the most sensitivity) ran at 220 nm that requires an LOQ (I'm not sure of LOD) of 20-30 ppm at a minimum. Can a DAD achieve that?
My general response regarding "which brand?" is to ask some more questions:
1. Have your current instruments been working well?
2. Has the vendor provided good support?

If the answer to both questions is "yes", then get the same brand; you will have fewer compatibility issues, a shorter list of spare parts, and greater familiarity with operation and software.

If the answer to question 2 is "no", then I'm sure lots of other people here will chime in with their suggestions/experiences.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Our other LCs are Jasco. They're the only HPLC systems I've worked with, so I don't have another point of reference. We've had issues with customer care/service, and the units are quite old; so I don't know if the parts we currently have will carryover.
Stupid question, but a DAD can be ran at only one wavelength as opposed to many correct?
Not stupid at all, but the answer is "yes".

Also, how is the sensitivity of newer DAD compared to UV detectors?
Other things being equal, a variable-wavelength detector will have an inherent advantage over a DAD by having a larger photodetector (gathers more light = lower "shot noise" = better S/N ratio. You'll have to look at the specs from your vendor(s) of choice, but my recollection is that the advantage is maybe a factor of 5-10. Note in passing that the Agilient "MWD" actually has optics very similar to their "DAD"

We have a method (our method requiring the most sensitivity) ran at 220 nm that requires an LOQ (I'm not sure of LOD) of 20-30 ppm at a minimum. Can a DAD achieve that?
Certainly -- if you inject a large enough volume. Okay, joking aside, LOQ and LOD ultimately come down to S/N ratio. Assuming a standard 1 cm optical path in the flow cell and bandpass / slit width on the polychromator / monochromator, the signal on any detector should be similar (yes, gross oversimplification). So look at the noise spec on your old Jasco, on the proposed new variable wavelength, and the proposed new DAD and that should give you an idea of how the LOQs will compare.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
We went through this process about three years ago after our old Varian became unreliable. Our choice ended up being Shimadzu over Agilent because of after-sale service and to this day we remain very happy with the decision. Will add were're not located in a metropolitian city, nor in the US. The situation may be different for you.
tom jupille wrote:
Stupid question, but a DAD can be ran at only one wavelength as opposed to many correct?
Not stupid at all, but the answer is "yes".


I'm retired now, but I think that our Agilent 1100 series DAD could be programmed for up to 5 wavelengths. And wavelength could also be time-programmed.
:oops: I misinterpreted the question as "is the DAD *capable* of running one wavelength at a time" (the answer is "yes") not "is the DAD *required* to run one wavelength at a time" (the answer is "no"). I think most DADs can, in fact, scan spectra "on the fly".
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
The obvious missing manufacturers from your list are Waters and Shimadzu. All manufacturers have several grades of instrument, and if sensitivity is important to you, then you should be considering the better-quality PDAs.
PDAs are naturally measuring the full spectrum continuously, but the software you're using will possibly place limitations on how you handle chromatograms at different wavelengths. For example, Agilent's Chemstation doesn't make it easy if you need to work with more than 5 (I think) different wavelengths, which it expects you to specify in the acquisition method (data are then collected at these wavelengths independently of spectra, which may also be collected; the advantage is that you can collect data far more rapidly to give a better estimate of peak shape. If you're used to VWDs, then Chemstation will feel quite natural). Meanwhile Shimadzu's software doesn't collect chromatographic data at fixed wavelengths separately at all; it simply collects spectra and expects you to specify, during data-processing, what wavelengths you need.
There are all sorts of other bells and whistles on the software side that might matter to you, or might be irrelevant. For example, Shimadzu can only subtract a single wavelength from all wavelengths you need for analysis, if you're in the habit of subtracting a blank, but they have some rather nice built-in stuff that, if you choose to use it (you don't have to) extends the dynamic range by deliberately looking at the "wrong" wavelength in very concentrated samples, and compensating for the reduced extinction coefficient by multiplying by the ratio of extinction coefficients at the "wrong" and optimal wavelengths as determined in a standard.
Software is actually as important as hardware; if you and your coworkers don't like the software, the instrument won't be a success. Another big difference is whether data are stored in individual files (Chemstation, Shimadzu) or a database (Waters, Thermo's Chromeleon, or Agilent's newer software. I still don't know which approach is best, but it has consequences for how you work and how you store your data.
Do check you can get appropriate support and training; Waters, for example, seem to regard PDA as specialist, and run separate (expensive) courses on how to use it.
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