How to validate the excel sheet using ASP.NET C#?

Question

i upload one excel document with more than one sheet and stored in dataset as data table.now i want to validate the dataset.<br /> if 'item no' is mandatory.the item number must be mandatory all sheets in excel sheet.<br /> if item number in 7 th row in all sheets but column value is different. how to validate,<br /> *All mandatory fields rows are same in all sheets but column is difference how to validate it.<br />