Systems/Experiments

The first part of a sample preparation system is to find a way to collect large numbers of samples using minimal resources.  In the case of obtaining samples from wet soil, we first attempted to pump the water directly out of the mud, although this led to clogging at the inlet before the filter clogged.  We managed to pump about 1mL of water using the system in Figure 1 before the system clogged.  Below is a flow chart of the system and photos of the setups.

Figure 1: Filter-based sample preparation

Figure 2: (left)Clog formed at inlet before reaching 0.2 μm filter,(middle) nylon cloth with 35 μm hole size. Clog quickly forms at inlet, (right)sump pump inlet with 400 μm screen.  Clogs much more slowly due to higher surface area, but enormous energy is required to fill internal volume with water.

Accomplishments

We tested pump, valve, and filter systems and developed a new system for low-moisture soil nitrate measurement.  We began programming the new electronics sensor board.  We produced an 8-channel fluidic multiplexer for calibrating the Amperometric Nitrate Sensor. We sourced bi-stable valves that take only 5.5mJ to switch.

Figure 3: Pumpless Filterless Sample Preparation

Figure 4: The metal screen protects the membrane from puncture.

Figure 5: An 8 channel fluidic multiplexer to be used as a calibration system for the Amperometric Nitrate Sensor.

Future Directions

• Test pump-less system that allows nitrates to diffuse into de-ionized water instead of pumping water out of soil.  This eliminates the need for filters since the dialysis membrane keeps out particles larger than its pore size.  It also prevents clogs from forming at the inlet, since water is no longer extracted from the soil. [March 2006 – July 2006]
• Program Sensor Board and integrate it into a wireless sensor network [April 2006 – August 2006]
• Develop a board level potentiostat to integrate into the Sensor Board [March 2006 – July 2006]

People

Jack W. Judy, Professor, UCLA
Michael Glickman, GSR, UCLA
Diwei Zhang, Undergrad, UCLA