For what purpose do you wish to use the split for?  Please attach some details/use case if possible.

1.  If splitting a string, and knowing which index of the array you wish to use; this will likely be simpler

http://community.k2.com/t5/K2-blackpearl/Inline-Function-in-K2-Smartforms/td-p/79772

http://community.k2.com/t5/K2-blackpearl/Split-a-String-using-K2-Designer-Expression/td-p/93104

2.  However if splitting a string, but there is a need to iterate through and do something with all values in the array; this will likely require additional considerations and will likely be more custom code heavy.