Retrive values from payment getway response using C# in ASP.Net

hi,

i have following response from one the payment gateway now i need to process this in my database field by field but i do not know how to break it it field

i want when response come then i can breaks into session like

session["merchant"] = successap_merchant.tostring();  

successap_merchant is come from response below as i need to break all the fields in different session in c#

successap_merchant=zyx&ap_custfirstname=Im&ap_custlastname=Iq&ap_custaddress=Ruby Street&ap_custcity=Karachi&ap_custstate=Pakistan&ap_custcountry=PAK&ap_custzip=74550&ap_custemailaddress=xx@gmail.com&apc_1=red&apc_2=&apc_3=&apc_4