There is a typo in the SELECT code, needs to be
SELECT Particulars,
LTRIM(RTRIM(SUBSTRING(
/* <text>> */ Particulars,
/* <start > */ CHARINDEX(';',Particulars,1) + 1,
/* <length> */ CHARINDEX(';',
SUBSTRING(Particulars, CHARINDEX(';', Particulars, 1) + 1, 99) + ';') - 1
) ) ) AS Result_string
FROM Sample_table