The 260/280 ratio reflects contaminations by DNA while the 260/230 ratio reflects contaminations by compounds that we can hardly eliminate entirely during the RNA isolation process (such as phenol or guanidium thiocyanate). Note that in both cases, the 260 absorbance, which is used to quantify your RNAs, is the numerator of the fraction. And in many cases, if you have low RNA concentrations, you have low 260 absorbance and the ratio is affected regardless of the actual RNA quality.

In your case, the second and third samples have decent ratios and should work well for RT-PCR. For the first sample, you may have low 260/280 and 260/230 ratios simply because you have a relatively low RNA concentration. For your third sample, though, you do have a very low concentration and yet a huge 260/230 ratio that could indicate contaminations by phenol or other compounds that may jeopardize the accuracy of your RT-PCR.

You can improve the quality of your already extracted RNAs (I would do this only for the third sample, here) by doing a precipitation with ethanol. However, you will lose some material during this process and this is therefore interesting only if you have enough material. There are also some column-based kits that can do this job, but again you lose some material.

Otherwise, low 260/280 and 260/230 ratios can be prevented by strictly observing the usual standard procedure during RNA isolation (preventing the action of RNases, for example, will improve the efficiency of the extraction, the quantity of RNA collected, the 260 absorbance, and both 260/280 and 260/230 ratios).

Hope this helps !

Hi Arun

Those commercial kits are optimised and will give good yield of RNA.

I would like to share few aspect which might help you for further trials.

Nucleic acids will absorb at 260 nm, 280 nm is for proteins, 230 nm is for other small molecules phenol or guanidium components). 260/280 shows the protein contamination in your sample, 260/230 will tell you the small molecules contamination. 

For DNA 260/280 is 1.8 is good quality, for RNA 2 is good quality. 

RNA Had uracil which absorb more at 260 which makes the difference between DNA and RNA absorption.

The following things u can try to improve your RNA quality.

The sample should be thoroughly lyse with lysis solution which is provided in kit.

During phase separation dont take the top layer completely, the middle layer has mostly protein and DNA.  

And finally u can give one more extra wash with washing solution, they might have given extra volumes, which can reduce the small molecular contamination.

These spectroscope photometer methods alone cont say how good is your RNA quality. 

i suggest you can run denaturing agarose gel electrophoresis to check your RNA is intact or not before you go for C-DNA and Real time quantification.

All the best