Dapper parameters not working

Dapper parameters not working

I'm trying to use the Dapper orm with the following simple query:
var sqlString = new StringBuilder();
sqlString.Append("select a.acct AccountNumber,");
sqlString.Append(" b.first_name FirstName,");
sqlString.Append(" b.last_name LastName,");
sqlString.Append(" a.rr RrNumber,");
sqlString.Append(" c.addr1 AddressLine1,");
sqlString.Append(" c.addr2 AddressLine2,");
sqlString.Append(" c.addr3 AddressLine3,");
sqlString.Append(" c.addr4 AddressLine4,");
sqlString.Append(" c.addr5 AddressLine5,");
sqlString.Append(" c.addr6 AddressLine6,");
sqlString.Append(" c.addr7 AddressLine7,");
sqlString.Append(" c.addr8 AddressLine8 ");
sqlString.Append("from (pub.mfclac as a left join pub.mfcl as b on
a.client=b.client) ");
sqlString.Append("left join pub.mfclad as c on a.client=c.client ");
sqlString.Append("where a.acct = '@ZYX'");
var connection = new OdbcConnection(_connectionString);
var result = connection.Query(sqlString.ToString(),
new
{
ZYX = accountNumber
});
However when I execute this with an accountNumber known to exist, dapper
returns nothing. So I tried to remove the quotes to verify that the
parameter is in fact being replaced with the account number, however the
error being returned from the server indicates a syntax error around
"@ZYX". Which means dapper is not replacing the parameter with it's given
value. Any ideas why this is happening? From the limited documentation out
there, this should 'just work'.