It depends on the type of cuvette you are using and your cuvette holder, because cuvettes are valid for a certain range of wavelengths.  I noticed that sometimes the cuvette holder can scratch disposable cuvettes when you insert them and automatically give an absorbance value when empty.  

First, just measure the absorbance without the cuvette. (blank first with nothing)

If absorbance > 0

            then you have a light leak

else if

            blank with no cuvette, insert cuvette, measure absorbance and if                                   absorbance > 0    

            then maybe your cuvette got scratched (check cuvette)

else

             do a spectral scan and see where the cuvette is absorbing

end statement

Can you go to the settings of your UV-Vis and do a lamp check, light leak check, and drift check?  If so, I would suggest that you do these to troubleshoot if the current code fail to compile correctly :)

 Dr. Farooq Wahab thank you for your attention there is problem when cuvettes of instrument  is without cells. I would appreciated for your opinion.

I agree with both answers, maybe my post was a little confusing, so let me clear my answer up for you.  You should blank with nothing then insert your cuvette and read the absorbance at your specified wavelength.  Yes there should be an increase in absorbance from the cuvette material but you want to note how much of an increase there is.  Next you blank with your empty cuvette, and read the absorbance  of your empty cuvette.  You should have an absorbance of zero, sometimes a negative number.  You should take at minimum, 3 consecutive readings of your empty cuvette.  If you notice that the absorbance is increasing, then you have to do some troubleshooting because there could be drift occurring with your instrument.  Try this and see what happens.  If there is no increase then you are good to go with measuring absorbance or transmittance.  Next, try the same thing, blank with empty cuvette, and then read the empty cuvette's absorbance 3 times but this time remove the cuvette and reinsert it after each reading.  If there is no increase in absorbance then your instrument is working properly and your sample holder does not have any nicks in it.  If you notice an increase in absorbance, check your cuvette for scratches because minor scratches can affect amount of light being transmitted to your detector which can give you false absorbance readings.  I know there are certain sample holders that can hold 2 cuvettes, one for a blank and the other for measuring.  Without more information, it is hard to answer your question.  If you could provide us with the following information, then we can probably help you troubleshoot any problems you are having?

What type of light source does your instrument have?

Does your instrument have a monochromator or does it use filters?

What type of cuvettes are you using (quartz, polystyrene or acrylic)?

What type of experiments are you trying to conduct with your instrument and at what wavelengths?

I feel that this information will be very helpful for you and other people following this discussion.  Hope this helps.

I also forgot to mention that with the old spec 20's, you had to record your sample blank aborsorbance and then record your sample absorbance.  You then determine the absorbance of your sample by this formula: Sample Absorbance - Sample Blank Absorbance.  I remember that you had to do this for every reading, blank then sample. I do not know how relevant this is to UV-Vis, but maybe someone can provide there expertise on this matter if it is relevant.

Mahboubeh Saeidi, good afternoon,

I realised that your question was 2 years ago... Anyways I would like to answer you at this time in case that other persons find this post, and help them if possible.

I am not sure about how much is the value of your non-zero absorbance, but recently, I was suffering a problem that I was having 10 ABS (maximum), and it was like a wild fluctuaction on the spectra, even when setting the zero at the beginning. In the page 32 of the hardware manual, there is a message showing that this happens when the 8-pin plug connector inside the device on the left is not well connected. This is related to electronic problems. I realised this was happening to our device. Try to fix well the cable or even repair it and may be your problems will be solved. 

Hope this can help anyone, 

Have a beautiful day!

Antonio

Dear colleague,

Thanks for your  attention.