using System.Text;

public class Program {

  private static string RemoveCommas(string value, 

                                     char comma = ',', 

                                     char quotation = '"') {

    if (string.IsNullOrEmpty(value))

      return value;

​

    var result = new StringBuilder(value.Length);

​

    bool inQuotation = false;

​

    foreach (char c in value)

      if (c != ',' || !inQuotation) {

        result.Append(c);

​

        if (c == '"')

          inQuotation = !inQuotation;

      } 

​

    return result.ToString();

  } 

  public static void Main() {

    var result = RemoveCommas("12,\"text, is\",\"another 25,000\",23,\"hello\"");  

    Console.WriteLine(result);

  }

}