low RNA concentration and low 260/230 ratio

[Piyawan]

Hi , Could someone give me some suggestion?
I purified RNA from lymphocyte (4x10^5 cells) I got 260/280 ratio around 1.8-2.0 and I got 260/230 ratio around 0.6-1.0 and RNA concentration 10-20 ng/ul by Nanodrop. I used RNeasy plus micro kit. I tried to wash twice with PRE buffer but the ratio 260/230 is still low as this ration is indicate that there is salt carryover. I tried many times but this ratio still low. However, with the high number of cells I got better value of 260/230 around 1.5. Does anyone know this ratio(260/230) is still low because of low concentration of RNA or not?
Thank you very much indeed
Piyawan

[relaxin]

I normally do not bother to look at the A260/A230 ratio. As long as the RT-PCR works, do not worry too much.
If the RNA concentration is too low, you can concentrate it by ethanol precipitation and redissolving in smaller volume of water.

[memari]

COPY, PASTE from Qiagen:
Effects of low A260/A230 ratios in RNA preparations on downstream applications:

The efficiency of downstream applications depends strongly on the purity of the RNA sample used. Pure RNA should yield an A260/A230 ratio of around 2 or slightly above; however, there is no consensus on the acceptable lower limit of this ratio. Possible candidates that can increase the A230 include “salt”, carbohydrates, peptides, and phenol (or aromatic compounds in general). In our experience, the increased absorbance at 230 nm in RNA samples is almost always due to contamination with guanidine thiocyanate, present at very high concentrations in the lysis buffer or extraction reagent used in most RNA purification procedures.

Please find an article discussing the effect of low 260/230 ratios in RNA preparations on downstream applications on page 7 of QIAGEN Newsletter 15, March 2010. In summary, we found that concentrations of guanidine thiocyanate of up to 100 mM in an RNA sample do not compromise the reliability of downstream applications.

http://www.qiagen.com/faq/faqview.aspx? ... Id=1000283