This webpage is an interesting summary:
Coffee, liver, antioxidants, benefits, health, caffeine

Questions I have:

1. Where in a coffee pour is the caffeine most concentrated - the initial 30ml (of a double shot), ie before the colour changes, the next 30ml, or the bitter water that follows? A url of the research helpful

2. Is the caffeine content changed by length of roast?

3. What is the different caffeine content of Arabica beans, Robusta beans?

4. Is there any information of the caffeine content of bean variety and growing region?

5. For equivalent weight of ground coffee, what is the caffeine content of Instant compared to freshly roasted Arabica?

References helpful to back-up comments.