PostgreSQL / PostGIS Update Syntax

Hi
I need to run the following update query on a PostgreSQL / PostGIS database

UPDATE geo_table
SET geom =ST_ConvexHull(
     ST_GeomFromText('MULTIPOINT(co_ord_string)', 4326)
);
WHERE 
Id =1234;

Select allOpen in new window

co_ord_string is a column name if I manually copy the row value into above the query runs otherwise I get

parse error – invalid geometry HINT: "MULTIPOINT(" <-- parse error at position 11 within geometry

I'm pretty sure this is because of the single quotes around  'MULTIPOINT(co_ord_string)' interprets co_ord_string as the literal string

The value of co_ord_string is a series of long lat points separated by a comma. These don’t create perfect polygons as they may contain internal points but using ST_ConvexHull a polygon is created


Could someone help with the syntax