Technical Note

Specificity of the Duquenois-Levine and Cobalt
Thiocyanate Tests Substituting Methylene Chloride
or Butyl Chloride for Chloroform

Amanda J. Hanson
Wisconsin State Crime Laboratory Madison
4626 University Avenue
Madison, WI 53705 2156
[email: hansonaj -at- doj.state.wi.us]

ABSTRACT: The use of alternative solvents in the Duquenois-Levine and Cobalt Thiocyanate tests were explored due to substandard results with recently purchased lots of chloroform. Methylene chloride provided satisfactory results when substituted for chloroform in both tests. Butyl chloride provided satisfactory results in the Duquenois-Levine test.

KEYWORDS: Duquenois-Levine, Cobalt Thiocyanate, Marijuana, Cocaine, Chloroform, Methylene Chloride, n-Butyl Chloride

Introduction

The Rapid Modified Duquenois-Levine test and Cobalt Thiocyanate test (Scott test) are proven screening tests for the presence of marijuana and cocaine, respectively. The organic solvent traditionally used in these tests is chloroform. However, chloroform recently purchased by this laboratory produced little or no color change when performing the Duquenois-Levine and Cobalt Thiocyanate tests. Shortly after opening, this chloroform became yellow to green in color, at which point it was unsuitable to perform these tests. According to the manufacturer, this unusual decomposition of the chloroform was due to insufficient amounts of preservatives. This experience led to the investigation of using alternative organic solvents, specifically methylene chloride and n-butyl chloride, in the Duquenois-Levine and Cobalt Thiocyanate tests.

Experimental

Reagents and Solvents
Hydrochloric acid, methylene chloride, and n-butyl chloride were obtained from Fisher Scientific. Acceptable quality chloroform was obtained from OmniSolv. The Duquenois reagent was prepared by adding 10 grams of vanillin and 5 milliliters of acetaldehyde to 500 milliliters of ethanol. The vanillin, acetaldehyde, and ethanol were obtained from Kodak, EM Science, and Fisher Scientific, respectively. The cobalt thiocyanate reagent was prepared by dissolving ten grams of cobalt (II) thiocyanate in a mixture of 490 milliliters of distilled water and 500 milliliters of glycerin. The cobalt (II) thiocyanate and glycerin were obtained from Aldrich Chemical and Fisher Scientific, respectively.

Procedures
The Duquenois-Levine test was performed on 17 different substances using chloroform, methylene chloride, or butyl chloride as the organic solvent. The test was performed by placing approximately 10 to 20 milligrams of a target substance in a glass test tube, then 10 drops of the Duquenois reagent. After shaking, 10 drops of concentrated hydrochloric acid were added, and the tube was again shaken. Any color that resulted after the hydrochloric acid step was recorded. Twenty drops of chloroform were then added, and the tube was vortexed, then allowed to settle and separate into two layers. Any color that transferred into the organic layer was recorded (Table 1). This procedure was repeated for each target substance by substituting methylene chloride or butyl chloride for chloroform.

The cobalt thiocyanate test was performed on 14 different substances using chloroform, methylene chloride, or butyl chloride. The test was performed by placing approximately 2 to 4 milligrams of a target substance in a glass test tube, then 5 drops of cobalt thiocyanate reagent. After shaking,1 or 2 drops of concentrated hydrochloric acid were added, and the tube was again shaken. Ten drops of chloroform were then added, and the tube was vortexed, then allowed to settle and separate into two layers. The final color of the chloroform (organic) layer was recorded (Table 2). This procedure was repeated for each target substance by substituting methylene chloride or butyl chloride for chloroform.

Results and Discussion

The results for the Duquenois-Levine test using either methylene chloride and butyl chloride were consistent with results obtained using chloroform. The marijuana became purple with the addition of the Duquenois reagent and hydrochloric acid. Upon addition of the organic solvent, the purple color transferred to the organic layer, indicating a positive test for cannabinoids. The color was consistent in all tests involving marijuana, regardless of the solvent used. None of the remaining 16 substances tested gave the characteristic purple color in the organic solvent layer.

Similarly, the results of the Cobalt Thiocyanate test were equivalent whether chloroform or methylene chloride was used. However, the results for the butyl chloride were mixed. Addition of the cobalt thiocyanate reagent to cocaine hydrochloride resulted in the surface of the particles turning a bright blue (faint blue for cocaine base). The solution changed back to pink upon adding one or two drops of hydrochloric acid and mixing. Addition of 10 drops of chloroform, vortexing, and allowing the solution to settle resulted in a blue organic layer for both cocaine hydrochloride and cocaine base. The test had similar results when methylene chloride was substituted for chloroform. In the case of butyl chloride, however, the organic layer stayed clear, giving an inconclusive test. Diphenhydramine and lidocaine also gave blue organic layers with either chloroform and methylene chloride. These compounds are known false positives for cocaine. However, in the case of butyl chloride, the organic layers were clear for diphenhydramine and white for lidocaine. The other ten materials had consistent negative test results for all three organic solvents.

Conclusions

Methylene chloride may be substituted for chloroform in both the Rapid Modified Duquenois-Levine test and Cobalt Thiocyanate test. Similarly, butyl chloride may be substituted for chloroform in the Duquenois Levine test. However, butyl chloride was not a reliable substitute solvent for use in the Cobalt Thiocyanate test. Methylene chloride also works well as an extraction solvent in place of chloroform.

[Tables 1 and 2 Follow.]

Table 1. Duquenois-Levine Test Results

	Chloroform	Methylene Chloride	Butyl Chloride
Material	aqueous/organic	aqueous/organic	aqueous/organic
Allspice	brown/clear	brown/clear	brown/clear
Celery Flakes	yellow/clear	yellow/clear	yellow/clear
Chamomile	yellow/clear	yellow/clear	yellow/clear
Chamomile Tea	yellow/clear	green/clear	green/clear
Coffee	brown/clear	brown/clear	brown/clear
Dill Seed	yellow/clear	yellow/clear	yellow/clear
Hops	yellow/clear	yellow/clear	yellow/clear
Ginger	orange/orange	orange/orange	orange/clear
Ginseng	brown/brown	green/clear	green/clear
Marijuana	purple/purple	purple/purple	purple/purple
Marjoram	yellow/clear	green/clear	green/clear
Mint	green/clear	green/clear	green/clear
Sage	yellow/clear	yellow/clear	yellow/clear
Salvia Divinorum	green/clear	brown/clear	green/clear
Thyme	yellow/clear	green/clear	green/clear
Tobacco	brown/clear	brown/clear	brown/clear
White Pepper	orange/yellow	orange/yellow	orange/yellow

Table 2. Cobalt Thiocyanate Test Results

	Chloroform	Methylene Chloride	Butyl Chloride
Material	organic layer	organic layer	organic layer
Benzocaine	clear	clear	clear
Cocaine	blue	blue	clear
Cocaine Base	blue	blue	clear
Dextrose	clear	clear	clear
Diphenhydramine	blue	blue	clear
Heroin	clear	clear	clear
Inositol	clear	clear	clear
Lidocaine	blue	blue	white
Methamphetamine	clear	clear	clear
MDMA	clear	clear	clear
Morphine	clear	clear	clear
Procaine	clear	clear	clear
Soap	clear	clear	clear
Sodium Bicarbonate	clear	clear	clear