Literature search problem: The purity of cocaine bought on the street varies dramatically. Cutting agents include levamisole, a compound normally used to kill parasites. Search the literature for a reversed-phase liquid chromatography method with diode array detection for the determination of the purity of street cocaine.

(a) Give the citation (authors, title, journal name, year, volume, pages) for the research paper that fits the criteria of this analysis.

(b) What alternative methods could be used for analysis of adulterated street cocaine?

(c) What is the range of purity of street cocaine?

(d) What type of analytical column was used for the analysis?

(e) How was the method validated?

(f) What is “robustness of an analytical method?”

Throughout the last few decades an increasing consumption of cocaine and seizures are observed in many countries. Street cocaine is traded as white powder which containswater-soluble hydrochloride salt or the water-insoluble cocaine base. To increase profit, it is often mixed with cutting agents (adulterants). These adulterants may reduce active drug content in the product or enhances effects of drug on human body. However, from the report of the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) it was noted that recently there is an increase in the use of the parasiticide levamisole as a new adulterant in cocaine. These adulterants possess effects that imitate cocaine's local anaesthetic effect, or enhances the cardiovascular and neuropsychiatric effects of cocaine. Prolonged use of levamisole causes health risks such as agranulocytosis and neutropenia to cocaine users,

Cocaine along with its adulterants, can be investigated on biological matrices by high performance liquid chromatography (HPLC) for a number of forensic applications.

(a)Citation:

Authors: Antonio Brancaccio, Paola Maresca, Stefania Albrizio, Margherita Fattore, Mario Cozzolinob and Serenella Seccia

Title: Development and validation of a diode array high performance liquid chromatography method to determine seized street cocaine sample purity

Journal name: Analytical Methods

Year: 2013

Volume: 5

Pages: 2584-2590

(b) The alternative methods that could be used for the adulterated street cocaine are Gas chromatography (GC) with flame ionization detection (FID), nitrogen phosphorous detection (NPD) or mass (MS) detection and HPLC with electrochemical detection (ED), ultraviolet (UV) or MS detection.

In this case a reversed-phase high performance liquid chromatography (RHPLC) method with diode array detection (DAD) was used to determine purity of cocaine street samples. Most of the analytes exhibit high molar absorptivity around UV-vis region. Detection of these analytes are much easier using HPLC-DAD.

(c) Between 10-20 mg of accurately weighted street cocaine the range will be within 95%-5%.

As per the least squares linear regression analysis of the data the following equation was developed y=12038x + 12.2 with a coefficient of determination (r ² > 0.9999), It indicates a good fit of the calibration function.

(d) An Agilent Zorbax Eclipse XDB-RP-C₁₈ column (150 mm × 4.6 mm I.D., 5 µm particle size) with aZorbax 5B-C₁₈ guard column (12.5 mm × 4.6 mm I.D., 5 µm particle size) was used as an analytical column in this research work.

(e) In this literature, validation of the method was performed according to the International Conference on Harmonization (ICH) guidelines. The main parameters of the validation procedure are specificity, linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy and robustness of the method and uncertainty. The purity match peak was observed at 999.722 for cocaine and 999.320 for levamisole. The LOD value was found at 0.004 mg mL^-1, corresponding to 0.4% w/w of cocaine in the street drugs. The LOQ value was found at 0.01 mg mL^-1. The intermediate precision was determined to be 2.9% and repeatability was less than 5%. A comparison between the results obtained by both HPLC-DAD and validated GC-FID methods are shown in a tabular format in the literature. Both the results were equivalent.

(f) The robustness of an analytical method is measurement of the capacity of the procedure to remain unaltered by minor, but intentional variations in method parameters and delivers an indication of its responsibility during normal usage.