There are several buffors for cell lysis containing TritonX-100 or Nonidet. We usually use 5M urea when we want to check  DNA content in the sample. That is a strong denaturating agent and that it might be a reason of low protein level in the sample. Of course it might depend of concentration but I you want to study proteins I will recommend standard buffors for lysis concerning a detergent Triton with isotonic condition of other buffor constituents and Mg ions as a protector for nuclei destruction. 

Dear Km Shams-Ud-Doha, 

Thank you for your consideration in the old thread:  https://www.researchgate.net/post/Why_cell_clumping_occur_when_washing_hemopoietic_suspension_cell_culture_with_1XPBS?.  Now that I found this your new question, I honestly have to ask about the real nature / properties [e.g. source / distributor, specified pH, and mosmol (tonicity), comosition=which ions added   -  producer's data -evtlly. own measurements] of your PBS (since - as you certainly know -  there are a lot of different 'PBS-formulations' out in the wild...Usually "1x PBS *) " is hypotonic (since approx.0.01M regarding at least sodium ions, cf. https://www.researchgate.net/post/Does_anyone_know_the_procedure_to_prepare_a_01M_solution_of_PBS2 ! so you perhaps should use 10x PBS *) + some sucrose if possible (cf. Re#002 by Michael Delannoy in the above mentioned thread @ https://www.researchgate.net/post/Why_cell_clumping_occur_when_washing_hemopoietic_suspension_cell_culture_with_1XPBS?).

For now, best of luck and regards, Wolfgang

NB (edited 5 min after original Re#01 above):

*)  Admitting that many cell prep-protocols use 1xPBS (without Ca and Mg), cf. eg. also: https://assets.contentful.com/an68im79xiti/56DlUZEsVOWc8sSG42KQis/c9d94a3dd5ca2cc1cdeff79f5a39dd2b/CG00053_Single_Cell_Protocols_Cell_Preparation_Guide_RevB.pdf

In eventu: "Centrifugation should be carried out at 4°C [or at least using a cooled/refrigerating centrifuge set at ambient Room/blood? temp.] to prevent overheating of the sample. (When precipitating from small volumes, centrifugation may be carried out at room temperature.)"

Relative centrifugal force (RCF):

"a method of comparing the force generated by various centrifuges on the basis of the speeds of rotation and distances from the center of rotation."

Don't know whether you would like to consider reading: e.g.:

https://www.thermofisher.com/us/en/home/life-science/cell-analysis/cell-isolation-and-expansion/sample-preparation.html; 

or: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4512735/    and more

Washing cell pellets generally mean you have to re-suspend the cells with the washing agent (usually PBS) and then re-centrifuge it. That way you can just decant or pipet out the PBS from the tube(s) without losing any cells. After washing is done, put some buffer to proceed to the next step. I am just trying to help you in a general way.

I agree with all the answers and would like to add more information. You can also lose the cells due to the handling. It depends on what kind of tubes you are using and How you are removing the supernatant. Sucking with the vacuum is the best way. If you use the pipette, there may be a chance of pellet disruption and losing cells. You also need to use a dark background while sucking the supernatant to see the pellet properly. Goodluck.

Dear Dear Km Shams-Ud-Doha, just to understand:  you do NOT (want to) lyse your cells during the washings, do you? .....(just thinking about the 1st reply by Malgorzata Rogalinska). Thank you for your consideration what I wrote in my Re# 2 above.

Dear Wolfgang H. Muss,

No, I don't want to lyse cell during washing. But I do lyse after washing which is not related to my question. I am particularly looking for a standard guideline for washing cell without disruption of the membrane.

Thanks.  

 Thanks everyone for your generous suggestion.