using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string input = "s:ds=\"{46C01EB7-6D43-4E2A-9267-608DE8AFA311}\" s:ds=\"{37BA4BA0-581C-40DC-A542-FFD9E99BC345}\" s:id=\"{C091E71D-4817-49BC-B120-56CE88BC52C2}\"";

        string regex = @"(?<=(s:ds=""{))([\d\w]{8}\-([\d\w]{4}\-){3}[\d\w]{12})";

        MatchCollection matchCollection = Regex.Matches(input, regex);

        foreach(var match in matchCollection)

        {

            Console.WriteLine("Collection Found : {0}", match);

        }

    }

}