XML序列化命名空间(C#)

<AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
<Header>
...
</Header>
</AmazonEnvelope>

我正在尝试这样的东西,但它并不完全正确：

XmlSerializerNamespaces nms = new XmlSerializerNamespaces();
        nms.Add("xsi","http://www.w3.org/2001/XMLSchema-instance");
        nms.Add("noNamespaceSchemaLocation","amzn-envelope.xsd");



        XmlSerializer serializer = new XmlSerializer(typeof(XMLAmazonEnvelope));
        StreamWriter writer = new StreamWriter(path);

        serializer.Serialize(writer,objectToSave,nms);
        writer.Close();

结果是：

<?xml version="1.0" encoding="utf-8"?>
<xsi:AmazonEnvelope xmlns:noNamespaceSchemaLocation="amzn-envelope.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<xsi:Header>
...
</xsi:Header>
</xsi:AmazonEnvelope>

这不是我想要的.
任何想法,应该采取哪些不同的做法？