Obviously HPLC is better. You can use it for identification, determination and separation purposes; but UV/Vis is applicable for identification and determination only. It can not separate the constituents of a mixture. So, if separation is not your headache, then go for UV/Vis, because it is less time consuming. But if you want to analyze an unknown compound, then use HPLC, because you don't know whether your unknown compound is a mixture of different compounds or not.

Although the HPLC flow cell has a short pathlength as compared to conventional 10mm cell but still it is 100s of times more sensitive as compared to a standard double beam spectrophotometer.....it can usually detect very small quantities of substance which normally go undetected in UV-VIs spectro. So even if separation is not your issue, even then you can use HPLC - although it is more time consuming.

Certainly hplc is best.

I agree with the other commenters on this post. HPLC-UV is GENERALLY much better than UV alone. Samples may be contaminated with other chemicals that absorb at the same wavelength to give a falsely high concentration of desired analyte in a UV protocol. HPLC gives the possibility of separating those interfering compounds away, or quantifying a series of related compounds in a sample. As mentioned above, HPLC also tends to be more sensitive.

Both require preparation of a standard curve. To measure UV, it´s a matter of absorbance at a wavelength. For HPLC, peak area is the response. 

HOWEVER:

It´s also important to keep in mind that HPLC is a more expensive method that requires equipment, reagents, and consumables that are more expensive than UV-Vis spectrometry. 

HPLC systems require more experienced technicians who know how to operate the equipment as it is more complex, has more moving parts, and has more points of failure. Experience is also necessary in selecting and using mobile phases and columns to get good separations and peak shapes. (Anyone can learn, but there is simply more to know). 

Also UV-Vis is much more portable than an HPLC, in case you want to take a field measurement. 

An additional advantage to UV-Vis is that it gives measurement results instantaneously, while you have to wait for an injection to finish running for HPLC. You can also do kinetic measurements more easily on a UV-Vis.

Sometimes UV-Vis and HPLC are used in a complementary manner to validate an experiment. 

I agree with Kiven in that HPLC is more accurate yet it is time consuming and expensive. If the substance you are analysing is single you better use UV but if in a mixture with unknown better use hplc

HPLC is the best

HPLC is a separation method coupled with a detector (generally UV/VIS). If you are absolutly sure that your theophylline is alone in the solvant (with no other compound) the use of HPLC is not necessary since there is no separation problem. 

I suggest you to hyphenate HPLC and UV. In order to improve the accuracy of analysis, guarantee the best fit of the analytical curve by ANOVA.

I agree with previous comments, in my opinion HPLC is better, it will be nicer if you used HPLC-DAD instead of HPLC-fixed UV detector; by using DAD detector the identity and purity of the target peak can be confirmed. After selecting the method, optimization of the method, I think you should do first validation of the method, before you can use as routine analysis. If you have LC-MS/MS than it is the best!

It depends on the concentration level of the theophylline and level of interferences you have got. If you do the determination of standard theophylline in solvent without complicated interferences you may use the UV-vis while using HPLC could solve  interferences and sensitivity is better

For precise results you will need to use HPLC, 1st prepare a HPLC method for Standard of your analyte, then run your samples in HPLC for minimum 3 times, so you will get three readings of the same sample, or for more accuracy number of readings can be taken more than three and finally you can get clear idea of concentration.

Second thing in case of using UV-Vis is not as much reliable as the HPLC is, because the interference of other compounds may interfere with the absorption of the analyte in sample. 

Best way go with HPLC and for curiosity cross check with UV-Vis you will get insight in both methods. 

Best Luck 

The answer depends on several factors, especially what is in the sample besides the specific material you are interested in. 

HPLC is better especially if you have the standard of the analyte  you want to analyze.

Please do not forget of evaluating the matrix effect. It can be done by recovery study.

hi tati

HPLC is realy better than UV/Vis

but absolutely HPLC is best for separation, identification and determination. 

but matrix of sample is so important to answer this question.

HPLC is definitely the better choice.  

Depends..

Basically in many practical situations, say for example, one has to analyze the product (analyte) from the reaction mixture (which may have many impurities/ side products and unreacted starting material along with the analyte). In such cases the UV spectra may overlap making it difficult or even impossible to quantify using UV-vis spectrometer. HPLC would be better option for such scenario as the analyte and other impurities will elute at different times making quantification possible. However, the sample analysis time for HPLC is higher than the UV-vis spectrometer. In another scenario where the impurities are less UV active or if the absorption spectra of impurities do not interfere with the lamda max of the analyte, in such cases UV-vis spectrometer will be a better option as it will save time compared to HPLC. In both cases, the accuracy of your results depend on your calibration chart. Hope this helps you..

It is obvious that the quantification by HPLC is better than that carried out by UV Visible.