The Week 76 Forensic Science Geek of the Week is announced

The Forensic Science Geek of the Week

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The week 76 “www.TheTruthAboutForensicScience.com Forensic Science Geek of the Week” honors goes to: Kim Keheley Frye, Esquire

: Kim Frye, Esquire

According to the website of Geek, the following is offered:

A proud Georgia native, Kim grew up in Cobb county and attended the University of Georgia and received her degree in Criminal Justice. As a law student at Georgia State University School of Law, she was a state finalist in the trial competitions with the Student Trial Lawyers Association and was a member of the Honor Court. Kim completed an internship with both the Fulton County Solicitor’s Office as well as the Southern Center for Human Rights. She was awarded a Governor’s Honor internship as clerk to the Honorable Judge Richard “Stan” Gault of the Blue Ridge Judicial circuit. Kim has been an assistant district attorney in Cherokee and Forsyth counties prosecuting felony cases in juvenile and superior court. Her experience as an assistant solicitor general in Cobb County included misdemeanor prosecutions of DUI, VGCSA, shoplifting, domestic violence and traffic offenses as the lead attorney. Kim has conducted over 40 jury trials. Kim’s passion does not end at the courtroom door. She has worked tirelessly as a volunteer and organizer for organizations and non-profits such as Due West UMC Treasure Chest, L’il Lambs Closet Consignment sale at First United Methodist Church, Sleighbells on the Square benefiting the Cobb Community Service Fund and the Junior League of Cobb-Marietta. She is a recipient of the 2006 Ruth Northcutt Community Service award. Kim is a member of the Georgia Bar Assocation, The Cobb County Bar Association, National Association of Criminal Defense Attorneys, National College of DUI Defense, the Georgia Association of Criminal Defense Attorneys and the Atlanta and Marietta Lawyers Club. She has been admitted to practice in the Superior Courts of Georgia, The Georgia Court of Appeals and the Supreme Court of Georgia. She also current sits at the President of the Solo/Small Firm section of the Cobb County Bar Assocation. Kim opened the Frye Law Group in 2008 for the sole purpose to defend the rights of the criminally accused. Kim’s significant training and experience on both sides of the judicial aisle allowed her to emerge as a seasoned advocate for each client’s rights.

Congratulations to our Forensic Science Geek of the Week winner!

OFFICIAL QUESTION:

: Forensic Science Geek of the Week Challenge

1. Identify this piece of equipment.

2. What is it used for?

3. How is it calibrated properly?

Our Geek of the Week answered:

Eppendorf Calibrated pipette.Used for correcting measuring the volume of liquid when preparing samples for gas chromatography and liquid chromatography. It can only be factory calibrated at factory. However, the calibration of the actual pipette can checked with a procedure to determine accuracy and imprecision. Each pipette can have a tolerance set by the user lab.

[BLOGGER’S NOTE: What a great answer. Thank you for participating. Congratulations on being our Geek of the Week.

Just to amplify, not to correct, I offer the following additional information.

A pippette is a volumetric delivery device for liquids used to hopefully deliver an accurate and precise measurement of that liquid. In forensic science and indeed all of science, a pippette is a crucial piece of equipment. If it is not routinely calibrated with a statement issued as to its calibration and bias, and then routinely checked to determine whether or not it remains within calibration, then all subsequent measurement and actions that are derived from the pippette cannot be deemed valid.

Modern mechanical pippettes such as the Eppendorf pictured above are mechanical devices. All modern mechanical pippettes generally come in two different types: air displacement based devices and positive displacement devices.

Air-displacement devices operate through the displacement of air through the mechnical use of a piston. They operate by use of a piston mechanism which is activated by either the thumb or hand and which subsequently generates a vacuum by vertical travel of the metal or ceramic piston within an airtight shaft. As the piston moves up, driven by the release of a plunger, a vacuum is created in the space left by the piston. This vacuum is then replaced by air. When a disposable tip is attached to the tip cone and immersed in liquid, the liquid is then drawn into the tip and subsequently dispensed by depression of the plunger. Proper use will achieve a precise vacuum through use of a piston, mechanical travel, springs, and rubber and/or polymer seals.

Positive displacement devices are similar to air displacement pipettes, but are less commonly used and are used to avoid contamination and for volatile or viscous substances at small volumes, such as DNA. The major difference is that the disposable tip is a microsyringe (plastic), composed of a plunger which directly displaces the liquid.

Due to their design, all of these devices are subject to ordinary wear and tear on the mechanical components and as they involve the delivery of liquids, there is even the possibility that there will be corrosion. Pippettes need to be cleaned and even decontaminated at times.

The photo above shows two pistons from a Gilson Pipetman which are both corroded and have blood contamination. This cannot be seen when a pipette is being used and care must therefore be taken in these procedures. All of these changes and more can effect the delivery of the volume of liquid and might even be undetectable to the end user.

Every reputable manufacturer should establish a Mean Time Before Failure (MTBF) to offer as general guidance to the end user in terms of the frequency to seek verification of calibration. There are some standards established for the conformity and usage of pippettes such as ISO 8655-2. As our Geek of the Week writes, most forensic laboratories wisely outsource the calibration of their pipeetes to third parties. If they elect to do so, then it should be outsourced only to an ISO 17025 laboratory. A certificate of calibration and bias is only as valuable as the process it undertakes. A reputable calibraiton service should report the calibration and bias of the instrument “as found” (meaning as it is discovered by the testing and calibration laboratory) and should issue a statement of calibration and bias of the instrument “as left” (meaning as it is released back to the originating laboratory). Eppendorf suggests the following process:

Prior to beginning your calibration, be sure that all components, pipettor, tips, balance and test liquid are temperature stabilized. The location should be out of direct sunlight, free of drafts and vibrations. The common test liquid is degassed, bidistilled water at room temperature. Determine the volume at which you will calibrate. Typically its at least two points. For adjustable pipettes, you may choose to do the nominal volume, approximately 50% of the nominal volume and/or the smallest adjustable volume which should not be less than 10% of the nominal. Fixed-volume pipettes and bottletop dispensers are calibrated at the nominal volume and multichannel pipettes are calibrated at the nominal volume and smallest adjustable volume.

Follow the steps below for proper calibration of your pipettor.

Attach the appropriate pipette tip to the pipette.

Set the pipette to the smallest volume which is to be tested (or nominal if only one point is to be used).

Tare the balance.

Pre-wet your pipette tip.

Aspirate and dispense the set volume three times and finish with a blow-out (reaching the second stop of the control button).

Hold the pipette in a vertical position in the beaker of water.

Immerse the tip so that 2-3mm is in the liquid.

Aspirate the test volume slowly and in a uniform fashion. Be sure to allow for a waiting period at the end of the aspiration to ensure completion.

Remove the pipette tip from the liquid slowly and again uniformly. Remove any drops that may be on the outside of the tip by wiping the tip against the beaker.

Place the filled tip at a 30 angle against the side of the weighing vessel (typically a boat or beaker).

Dispense the test volume slowly up to the first stop and again allow for a waiting period at the end. Press the button to the second stop to dispense any remaining liquid.

While holding the control button at the second stop, slowly drag the tip along the inside of the weighing vessel to remove it.

Record the value that appears on the balance display after it has stabilized.

Repeat steps 6 through 13 until youve completed your series.

Evaluate the inaccuracy and imprecision. Do the same with other volumes if required.

Calibration is predominantly undertaken by gravimetric analysis and is the method most commonly used. Gravimetric analysis for pipette calibration entails dispensing samples of distilled water into a receiving vessel in a precision analytical balance. The density of water is a known constant, the temperature, barometric pressure and humidity are recorded (the Z-factor used in the final mass calculation) and kept within certain limits and thus the mass of the dispensed sample provides an accurate indication of the volume dispensed.

The very best ISO 17025 calibration laboratories conduct their calibration of pippettes in a Calibration Room. As an example of environmental conditions and equipment the following would be typical of an accredited laboratory: