How to check if a node exist in array list in XML response

Need to check the duration node exists in the response as below
<cns:PaxJ1>
<cns:D1 UnitCode="Miles">1442</cns:D1>
<cns:Duration>PT05H43M</cns:Duration>
<cns:PID>FLTd3005a05ebf03</cns:PID>
<cns:PRefID>SGMd1005a05ebf03</cns:PRefID>
</cns:PaxJ1>
<cns:PaxJ1>
<cns:D1 UnitCode="Miles">1452</cns:D1>
<cns:Duration>PT05H63M</cns:Duration>
<cns:PID>FLTd3yy5a05ebf03</cns:PID>
<cns:PRefID>SGMd1133405ebf03</cns:PRefID>
</cns:PaxJ1>