Canfer,
You can make any type of measurement with the ADS1234 as long as the input to the ADS1234 is within the analog input voltage range of the device. This is shown in the Electrical Characteristics table on page 3 of the datasheet under the Parameter Common-Mode Input Range. If you use a gain of 1 or 2 your input voltage can range from AVSS-0.1V up to AVDD+0.1V. For higher gains the input voltage must be greater than AVSS+1.5 and less than AVDD-1.5V. Of course the difference between AIN+ and AIN- must be within the measurement range relative to VREF and gain used.
For example, if AVDD is connected to +5V and AVSS is connected to GND, then when using gain of 128, the inputs must be within 1.5V and 3.5V.
Best regards,
Bob B