Are you collecting qualitative or quantitative data? There has been quite a lot written on this topic in qualitative research.

أي نوع من العينات؟

the study is quantitative survey. Likert scale. is there a reference.

or is this situation calls for a purposive sampling where you want to select a certain profession from both public and private sector. any reference study.

In survey research terms, you are defining the population from which you want to sample. The term "purposive sampling" is typically limited to qualitative research.

I think a lot depends on what the typical practice is in your field. Do other researchers in this area have access to random samples from known populations? If not, then this is unlikely to be a meaningful criticism of your research.

i have conducted a study on the IT industry, both public and private sector organisations.

selected some public organisations that have adopted technology for service delivery to public to reflect development in country....unit of analysis is individual.... so visited organisations and got a convenience sample.

selected a private sector trade association and got a list of registered member organisation. and on basis of convenience drawn a sample from them.

i am from management sciences.

now i dont know what exactly to call this random sampling technique as total population cannot be known.

thank you.