The pH test works with U.S. antifreeze of the older formulations...around 9.0 to 10.5. Many modern formulations and the Japanese antifreezes are around pH 7.
What does work to determine the state of the corrosion inhibitors is to use a voltmeter. Put one probe in the cool coolant in the radiator neck--don't touch metal. Put the other probe on the negative battery post. If you measure 0.1 volts DC, you're good. If you measure 0.3 to 0.4 volts, it is time to renew the coolant. The voltage is being generated by galvanic corrosion in the engine.
Ken