SQL & PL/SQL :: Using Apostrophe / Quotes In A String

Here is a sample function which takes in a string of CSV fields and prints the third field :

create or replace function restr(istr varchar2) return INTEGER
is
var_1 varchar2(30);
begin
dbms_output.put_line('input:'||istr);
select regexp_substr(',' || istr,1,3,null,1) into var_1 from dual;

[Code]..

When I pass an input string as :

JOHN,MARY,O'DONNEL,O'CONNELLY,MARK

with quotes/apostrophe in it to the function then it prints the input string in the first dbms_output but errors out at the select with ORA-01760.

how we can use the quote/apostrophe character here ?