Creating a superscript in mtext

Question

I have the following dataframe

Data1 <- data.frame(pH = c(8,8.5,6,7.1,9), EC50 = c(20,11,5,25,50))
Data2 <- data.frame(pH = c(7,7.2,6.5,8.2,8.5), EC50          


        

Answer 1

You have to build your expression within the expression call. See the examples at Mathematical Annotation in R.

In your case I found

mtext(expression(paste( plain("Cu") ^ plain("2+"), plain(" at EC50") )), side=2, line = 4, padj=1, at=30, cex=1.2)

gave a reasonable result

Answer 2

mtext(expression(paste("Cu"^"2+","at EC50",sep="")))