Arduino Portenta H7 Increase ADC sampling

Hi I'm using the arduino portenta with the Arduino IDE, even though the board has a core with a 480 MHz clock and built in ADCs that support 3.6 MSPS I'm only able to read from the ADC pin using analogread(0) at around 8 ksps. Can I increase the clock speed of the portenta used in the arduino IDE, how would I best approach upping the sampling to around ~1 MSPS (looking for 16 bit resolution around 100 kHz sampling rate). How would I best approach this?