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Introduction

For most of their professional careers, many people in the field of latent print processing have been using a recommended formula for Ninhydrin mixed with the solvent, Freon (CFC-113). After a while, Freon (CFC-113) became very expensive to buy and then became impossible to purchase because it was determined to be an ozone-depleter and was banned in several countries. Technicians tried other solvents but few had all the advantages of Freon (CFC-113). Many technicians felt that these substitute solvents gave inferior results for developing latent prints.

The scientists at 3M have produced a safe, non-ozone-depleting solvent. This new solution is called 3M™ Novec™ Engineered Fluid HFE-7100. You may have read the published results from experiments conducted by the Police Scientific Development Branch in the United Kingdom. [See the Journal of Forensic Identification, Vol. 47, No. 3, May/June 1997, pages 287-306 for two articles.]

The authors of these articles found that using 3M™ Novec™ Engineered Fluid HFE-7100 in mixing Ninhydrin has "significant advantages over formulations based on hydrocarbons in terms of efficiency and, more importantly, safety." [Hewlett, et. al., "Replacements for CFC113 in the Ninhydrin Process: Part 2," Journal of Forensic Identification, 47 (3), 1997, p 300.]

The Home Office Manual of Fingerprint Development Techniques states, "The recommended formulations use solvents which are safe and effective. The HFE-based formulation is an effective replacement for the CFC-based formulation previously used in this process. The CFC solvent is being phased out under the terms of the Montreal Protocol on substances that deplete the ozone layer." [©1998, Title Page of Ninhydrin Section in the Manual]

In Fingerprint Whorld, the authors proposed a formula for mixing DFO in 3M™ Novec™ Engineered Fluid HFE-7100 as a replacement solvent for CFC type solvents. [Claude Didierjean, Marie-H$8Elene Debart & Frank Crispino, "New Formulation of DFO in HFE-7100," Vol 24, No. 94, October 1998, pages 163-167]

The need for a substitute solvent for Freon (CFC-113) has been acknowledged across the globe and now the replacement solvent of 3M™ Novec™ Engineered Fluid HFE-7100 has been scientifically acknowledged as the appropriate replacement. 3M™ Novec™ Engineered Fluid HFE-7100 has zero ozone depletion potential, low global warming potential (GWP), low toxicity and is nonflammable. This is not just a temporary fix to an environmental problem. This solvent was designed as a long-term solution to a significant problem.

Special Instructions for Mixing

For suggested formulæ for mixing DFO and Ninhydrin with 3M™ Novec™ Engineered Fluid HFE-7100, see our DFO and Ninhydrin Processing technical notes. These formulæ have been tested over a period of time and have proven to be effective. However, there are a few special techniques that you will need to do be aware of to effectively mix 3M™ Novec™ Engineered Fluid HFE-7100.

Post-Mixing Instructions

After you are finished mixing either Ninhydrin or DFO as per the instructions on Pages 32 and 20, follow these instructions as given to us by the chemists at 3M. Cover and allow the solution to settle for approximately 30 minutes. A thin, oily-looking film may form on the top of the solution. This film consists of water, excess ethanol or methanol and Ninhydrin or DFO and must be removed prior to use. The film can be removed by any of the following procedures.

1)If available, process the working solution through a separatory funnel. To do this, pour the solution into the funnel, then again, allow the solution to settle for at least 30 minutes. Drain the bottom layer into a squirt bottle or storage container. Stop draining when this separate, clear-looking solution nears the bottom of the funnel, or approximately 50-100 ml of solution remains in the funnel. The remaining solution should be discarded in a proper waste container for flammable solvents as it consists of undissolved ethanol or methanol, water and Ninhydrin or DFO.

2) If a separatory funnel is not available, use a pipette to skim the oily film from the top, again discarding the waste in a proper waste receptacle.

3)If neither a separatory funnel nor pipette is available, simply transfer the solution into a squirt bottle. This will help insure a clean solution. When the solution level is below the straw in the squirt bottle, discard the remaining solution in a proper waste receptacle.