Tech Challenge

Tech Challenge

Extracting DNA Samples

Larry from Labotech Logistics is extracting DNA samples for forensic research. Since DNA is pH sensitive, the researchers are using Tris buffers to stabilize the pH of the samples he prepares. Recently they had a problem with the effectiveness of their buffers and lost several DNA samples. They can’t afford for this to happen again, so Larry wants to check the pH quality of his samples throughout the process. 

Larry dusted off an older pH meter, but it was missing an electrode. What type of pH electrode should Larry purchase when working this type of application?

A: A low-cost single-junction electrode.

B: Any combination pH electrode with built-in ATC (Automatic Temperature Compensation).

C: A calomel (mercury chloride) electrode

D: A double-junction electrode

Answers:

A: A low-cost single junction electrode.

Incorrect. Although the single-junction electrode will take a proper measurement, it won’t last very long. The single junction will clog quickly and the electrode will need to be replaced more often. Try again.

B: Any combination pH electrode with built-in ATC (Automatic Temperature Compensation).

Incorrect. Not every electrode is recommended for working with Tris buffers. Temperature is very important, however, and an ATC probe should be measured along with nearly all pH measurements. When purchasing an ATC probe it is important to make sure it is compatible with the meter you are using.

C: A calomel (mercury chloride) electrode.

Close. This was the favored choice to use with Tris buffers, but tighter restrictions on the manufacturing and use of products containing mercury have made this type of electrode less of an effective option in today’s marketplace.

D: A double-junction electrode.

Correct. A double-junction electrode will prevent clogging to ensure longer life of the electrode.  It is also recommended that an ATC probe be used as well.  When purchasing an ATC probe it is important to make sure it is compatible with the meter you are using.  Depending on the meter, the ATC probe can be separate or built into the pH electrode

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Securing Samples from Groundwater

Sandy from Superior Environmental Samplers is looking for a pump to pull up samples from various groundwater wells across a site. She will be running a series of quality tests on the water and looking for harmful contaminants. The wells range from 5 feet to 15 feet deep.

What type of pump would work best for this type of application?

A: A gear pump

B: A double diaphragm pump

C: A peristaltic pump

D: A centrifugal pump

Answers:

A: A gear pump.

Incorrect. A gear pump doesn’t have the ability to pull the suction lift. Plus it does not handle particulates typically found in groundwater.

B: A double disphragm pump

Close. This type of pump would be able to generate the suction lift required, but also requires air power which would mean hauling around a compressed air tank to get the unit to operate. It also may potentially contaminate samples as cleaning the pump after use is more difficult than other pump technologies.

C: A peristaltic pump

Correct. A peristaltic pump is the best choice for this type of application. Peristaltic (or tubing) pumps are great for providing suction lift (the ability to pull fluid up). Since only the tubing comes into contact with the fluid, clean up is easy. The pump is also very versatile because a wide variety of tubing is available to use with it. For sampling applications, the use of silicone tubing makes contamination-free sampling a breeze. The Masterflex® E/S® Portable Sampler has everything Sandy will need to work from the field, and even offers an optional automotive power adapter for charging or operating in the field.

D: A centrigugal pump

Incorrect. This type of pump will be unable to generate any suction lift. Centrifugal pumps are great for moving large volumes of fluid across a distance or through a system at high flow rates, but lack the ability to pull fluids up.