There is an enormous practical difference between a single or multi-wavelength detector and a real scanning diode-array detector. If you plan on doing any HPLC method development or operate in a regulated environment, a diode array type of UV/VIS detector (DAD or PDA) is usually the best choice as a primary HPLC detector. A single wavelength detector is of very little value in HPLC method development (IMHO: a waste of money and very poor utility in the lab). The main reason for this is that a DAD/PDA can always be set to scan a range of all probable wavelengths, but a single (or multi-wavelength) detector can not. If you just use a single wavelength detector to monitor your method, then you will NEVER know what samples are present or even if the peak you are detecting is the correct one. The data generated by a correctly set-up DAD/PDA can alert you to new or existing possible impurities, changes in product, changes in the method and HELP you to develop proper HPLC methods. A DAD/PDA is one of the best purchases you can make.

I think UV-VIS can measure two different wavelength at the same time. It has also lower noise level than DAD.

thank you so much, thats why I am asking that to which system should I pay money... Since I used both of them but couldnt see big difference... DAD may provide me checking extra wavelengths in my samples, paying almost double :)

Depending on the software, a diode-array detector can measure across all the wavelengths at once. I once used a Waters HPLC system that displayed a UV-vis spectrum once a second during the purification while monitoring a single wavelength. It was useful for seeing the occasional peak whose absorbance wasn't the lamda-max for the natural product mixture. As mentioned above, UV detectors measure only a couple of wavelengths where your active compound may not absorb. Often the UV detector is fixed at 254 nm; a diode array lets one choose the absorbance wavelength. For example, someone purifying carotenoids would find they may miss the compounds because the absorb at ~470 nm and possess no UV absorbance.

Depending on the software on the HPLC, diode array detection can also give better purity data by correlating the spectra than ratioing two UV traces because more data is compared in the two datapoints.

The main difference is the ability to identify compounds based on spectral data obtained by the DAD. I always use DAD because it gives me more information about purity of peaks, and it gives me the confidence in compounds identification. The price is not so high if you will need to take spectral data and plan to analyse mixture of compounds visible at different wavelenghts.

I am facing problem of getting concentration/calibration curve of pure Coenzyme M (Co-M, mole wt 164). Last time I had used the Agilent HPLC with DAD detector at 270 nm wavelength and I had received the good linear concentration curve that was passong from the origin and this time I have used different Agilent HPLC machine with UV detector, but not getting linear concentration curve. Same column (C-18, 4.6x250 mm, 5 um) used during the both analysis. What will be the possible reason for not getting linear concentration curve? Please share your experience.

Hi Tatoba, similar problem here. The HPLC made and column is same as you described. The wavelength of my compound (a herbicide) is 229 nm in DAD. Some people tried with 282nm using UV-Vis. I set that wavelength in DAD as well. Good peak is coming with gradient mobile phase. But same problem, not corresponding to the concentrations. I also appreciate if anyone share similar experience and probable solutions.

There is an enormous practical difference between a single or multi-wavelength detector and a real scanning diode-array detector. If you plan on doing any HPLC method development or operate in a regulated environment, a diode array type of UV/VIS detector (DAD or PDA) is usually the best choice as a primary HPLC detector. A single wavelength detector is of very little value in HPLC method development (IMHO: a waste of money and very poor utility in the lab). The main reason for this is that a DAD/PDA can always be set to scan a range of all probable wavelengths, but a single (or multi-wavelength) detector can not. If you just use a single wavelength detector to monitor your method, then you will NEVER know what samples are present or even if the peak you are detecting is the correct one. The data generated by a correctly set-up DAD/PDA can alert you to new or existing possible impurities, changes in product, changes in the method and HELP you to develop proper HPLC methods. A DAD/PDA is one of the best purchases you can make.

I want estimate citric acid, succinic acid and gluconic acid. Can I analyse by Hplc without the help PF DAD?. At least citric acid?. Can I use column of 5um particle size, 150 4.6 mm I.D., size in place of 3um particle size 150 4.6 mm I.D. for detection of citric acid? 

Hi sir,

1. The UV/Vis detector can detect  single wavelength at one time while the DAD can scan a wavelength range (i.e. 190-800nm). DAD is actually a UV/Vis detector it has an array of numerous photodidoes.

2. DAD will scan all the compounds which can respond in the given wavelength range (say 190-800 nm) there is no need of any adjustment. It will adjust by itself.

3. Both these detectors are equally easy to operate or interpret. But DAD is better than UV/Vis because it can scan whole 190-800 nm region, on the other hand, UV/Vis can scan a single wavelength only. so if you want to scan a wavelength range DAD is better option. But if you know the absorbance wavelength than you can detect that single wavelength by using UV/Vis detector.

In method development, DAD is a better choice because UV/Vis detector is very time-consuming. So for development a new method, I strongly recommend you to use DAD.

Mr. Yucesan,

Please, consider this discussion:

https://www.researchgate.net/post/How_to_analyse_phospholipids_PC_PE_PI_on_HPLC