How to say in Russian "I have a quick question for you Irina"?
a quick question = короткий вопрос
It's better to use 'Ирина, у меня к Вам короткий вопрос, (когда вы пойдете на концерт сегодня? - Мы не пойдем.)'
'Короткий' means that we are expecting a 'короткий' (short [in time] = quick) answer as well.
'Ирина, у меня к Вам небольшой вопрос' is closer to "I have a short question for you Irina" (short to ask, but not necessary short to answer).
And keep in mind that in Russian 'небольшой вопрос' could be more than just a question, it could be a request to do something: 'Ирина, у меня к вам небольшой вопрос, не могли бы вы выйти на работу в воскресенье?"
Update. If you and Irina are on different levels of a hierarchy in that case the most likely meaning of 'небольшой вопрос' is 'a small business': if Irina is on a higher level - she will expect a request to do a favor ('Ирина, у меня к Вам небольшой вопрос. Я принес заявление на отпуск в июле, не могли бы вы его рассмотреть и одобрить сегодня? - Хорошо, оставьте у секретаря, и подходите после шести, тогда мы рассмотримм ваш вопрос.)', if she is on a lower level - an errand will be expected (less common). I guess that ritual came from soviet bureaucracy (newspeak): 'Товарищи, вы по какому вопросу?' (what business brings you here?) On the same level of hierarchy (or no hierarchy) you could be straightforward "I have a small business for you Irina".
'Quick question' is a colloquial English term. According to Urban Dictionary it is a question that usually requires a long answer.
@naXa: I vote for your example:
I.e. using a common expression: всё хорошо, только у меня к Вам один маааленький вопрос: ... (with a snide; the asker knows that his question can't be easily answered)
Ирина, у меня к вам небольшой вопрос. - More neutral
Ирина, у меня к вам вопросик. - More informal
DO NOT put the name at the end of the sentence. It's not grammatically wrong, but we never, never do that, so it'll be a dead giveaway that you're not a native speaker.
DO NOT use 'короткий вопрос'. Same as the previous one, we just don't use it like that. Ever.
You can leave out the name altogether. In Russian it's not natural to call a person by their name all the time. If you're talking to someone, just look at them, and they'll know you're talking to them and not a nearby wall. No need to call their name unnecessarily. Honestly, it's annoying and feels like you can't remember the person's name and have to repeat it all the time. If you're trying to catch a person's attention, it's fine to call their name, but, please, don't repeat it all the time.
So, if you're already talking to that Irina, you can say just:
У меня (к вам) (небольшой) вопрос. or У меня (к вам) вопросик.
You can easily leave out the parts in brackets. In Russian it's natural to leave out a lot of things if they can be read from context, and in this case it's: 1) already obvious that you have a question for Irina, because you're talking to her, so there's no need to use 'к вам'; 2) it's not really necessary to specify that the question is short unless Irina is really short on time.
Actually, you can also leave out 'у меня', because it's obvious that it's you who has the question. Which leaves...
Вопрос. or Вопросик. But these two are rather informal.