<?php
	require 'wp-load.php';
	
	add_action('wp_ajax_mysettings_save' , 'mysettings_save');
	
	function mysettings_save() {
		//DO SOMETHING USEFULL HERE
		exit('It worked!');
	}

?>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7/jquery.min.js"></script>
<form>
	<p><input type="text" name="my_settings_field" value=""></p>
	<button>Save</button>
	<?php settings_fields('my_settings'); ?>
</form>
<script>
	$('form').submit(function(event){
		event.preventDefault();
		
		$.post('wp-admin/admin-ajax.php?action=mysettings_save', $(this).serialize(), function(data){ console.log(data); });
	});
</script>
