A 260= For DNA

A 280= For Protein

It's low values for A260/280 is of concern because mathematically higher protein contamination will bring this value down indicating protein contamination. You will be fine for downstream analysis. 

Thankyou. I wikk work on eliminating protein fron the sample...

You don't need to.

But you pointed out that low ratio is because of high protein content... Any suggestion on how I can take care of that?

You don't have a low ratio for some of the samples. If you are doing PCR for samples with 1.5, then you can try to do PCR with the 1.9s + 1.5 samples and see if lower purity effects the reaction. You can try to re-extract the ones with lower purity using the same columns, or just re-run those samples are purify. Typically you should be harvesting a little bit more samples than you need in anticipation of events like these. 

"Nucleic acids and proteins have absorbance maxima at 260 and 280 nm, respectively. Historically, the ratio of absorbances at

these wavelengths has been used as a measure of purity in both

nucleic acid and protein extractions. A ratio of ~1.8 is

generally accepted as “pure” for DNA; a ratio of ~2.0 is

generally accepted as “pure” for RNA."

http://www.nanodrop.com/Library/T042-NanoDrop-Spectrophotometers-Nucleic-Acid-Purity-Ratios.pdf

You can try to add those samples with lower purity to the columns you have and re-run it from start. Alternatives are 

http://bitesizebio.com/142/5-ways-to-clean-up-a-dna-sample/

Thanks, I will do that.

Dear Ayesha, if you have recently started or involved in the field of qPCR, then you asked this question at a very right time. I would like to address this question in a different way based on my experiences to reveal some of the facts and issues hidden in this query you have raised.

For an ideal template (cDNA) required for the qPCR, along with RNA quality, the quantity (concentration) of RNA also matters, which you did not mention here so assuming myself that you are having good concentrations for your RNA samples.

Just on the basis of good A260/280 ratios for RNA proceed to qPCR directly is not very wise, but one may proceed if wants as the choice is yours. If your qPCR gives good screenshots so consider you are really lucky, but what if despite of having good RNA A260/280 ratios you gets an irritable qPCR result, which is also not very uncommon, so here a huge waste of your time, efforts and resources you just encountered. So now, it’s time to relook multiple steps in this entire cycle starting right from the RNA extraction protocols till your cDNA template is finally ready and diluted appropriately to be run for qPCR along with your GOIs and HKG (reference) primers.

Unless you won’t run your RNA on gel or check on Agilent Bio analyzer (estimation for RIN values) you will not have true conclusion about your RNA integrity. The choice of selecting cDNA (RT) kit and RT Enzyme is another key decisive approach that you need to care about. As, if your final template is not having good quality, so there is no benefit of your excellent A260/280 ratios of RNA at all.

By literature point-of-view an ideal A260/230 for RNA is usually above 1.5 so technically you are safe as the data you have provided.

 Judgments based on simply looking over A260/280 or 260/230 and supposing that everything is good, is less scientific and less logical, as there are several factors exist for the increase and decrease in A260/280 and 260/230 values despite of having good RNA in actual integrity wise. So this procedure is very prone to give you false positive and false negative readings, so never rely 100 % on such readings. For example;

For a same sample, these ratios may fluctuate by using a different analyzer other than you have used for your samples so a reliability doubt exits in the measuring unit itself.

RNA dilutions done in RNAse free water decreases the A260/280 values, a known fact.

RNA dilutions done in a buffer then later blank the instrument on simple water (nuclease free) decreases A260/230 values.

Measurements taken, while the blank pedestal is dirty may result in decrease A260/230 values.

Residual phenol in your extracted RNA may increase A260/280 values.

Also your extracted RNA may have a very impressive A260/280 reading but invisible residual contaminants in this sample may inhibit your RT step or even the qPCR later without any visual explanation. So here you are in a mass trouble.

 It is always advisable that whenever you have RNA in your hands so prepare cDNA immediately and store it properly (preferable at – 80C in small aliquots) to avoid any further potential loss in your RNA.

 To check your RNA and cDNA are good we also adopt one approach that after having your cDNA, make its desired dilutions as per your assay and run this diluted cDNA on a conventional PCR using the conventional master mix for all GOIs and HKG of your study by using the respective primers designed for qPCR. Use the same cycle conditions and cycle numbers for this conventional PCR run, as mentioned in your qPCR machine program, but here try to create a thermal gradient with 1-2 C for all the primers Ta (annealing temperature) to check which Ta is actually best fitted for your primers and then run qPCR with that Ta only to avoid any chance of mispriming later in your qPCR. 

 With Regards and Good Luck...