I was browsing Digikey the other day (don't you?) and I stumbled across some 32bit ADCs, there were offerings from Linear, TI and Analog. One stood out, the AD7177 from Analog which states in Table 7 on page 19 of the datasheet that at 5 samples per second it's got a staggering 27.5 effective number of bits (and an RMS noise of 50 nanovolts). On the other hand of course, it's accuracy is significantly worse, but still.
This got me wondering, if a relatively cheap off-the-shelf ADC can hit an ENOB of 27.5 bits...
What's the highest ENOB ever achieved? Be it in some super integrated IC, some piece of stupidly expensive lab gear, a lock-in amplifier? Has anyone ever beaten 27.5 bits of precision?
 A bit of clarification I'm not looking to buy/build or otherwise aquire such a device I'm just curious what the current state of the art is, modern atomic clocks have hit 3x10-18 (3 quintillionths) uncertainty, where do modern scientific voltmeters sit on the scale?