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This essay will attempt to defined what is meant by the term profiling in context to seized drugs in particular reference to heroin, before going on to explain clearly why such information is of value to the police, and finally to review the various analytical techniques that can be used in the profiling of drugs in reference to heroin along with their application.
Drug profiling refers to the systematic extraction and storage of chemical attributes of drugs seized in order to obtain indications on the manufacture and distribution processes, the size and the evolution of the market and whether the seized drug originated from the same source [1, 4, and 16].
In respect to Heroin profiling can be of two types which are impurity and chemical profiling. Impurity profiling usually involves several analyses that are designed to produce a detailed picture (profile) of a drug sample, usually in the form of a chromatographic data. The resulting chemical profiles, also known as "signatures" or "impurity profiles" result in the identification and usually the quantification of major components in the sample. Impurity profiling also include one or more additional analyses designed to target the minor (trace) components in the sample [4, 5].
Chemical profiling of a sample is understood to be the profile of the co-extracted and manufacturing impurities (impurity profile), and the cutting agents. It is a chemical link between samples. At the international level, the samples may represent products from different manufacturers brought together for final processing and/or distribution as a single consignment. If the samples are seized at different levels in the distribution chain Chemical profiles of the samples coming from a common source may differ, or if the samples are distributed in different chains. Cutting agents may be added at different stages of distribution, and different cutting agents may be added by different dealers. Consequently, samples will have the same relative proportions of co-extracted and/or manufacturing impurities but are likely to contain different cutting agents. While such samples are probably related by source, they are unrelated by distribution and do not have the same "history" [13, 15].
Heroin can be defined as an opiate drug that is highly synthesized from morphine, a naturally occurring substance which is extracted from the seed pod of the Asian opium poppy plant. It is a "downer" or depressant that affects the brain's pleasure systems and interferes with the brain's ability to perceive pain. Heroin usually appears as a white or brown powder or as a black sticky substance, known as "black tar heroin" [11, 12].
Drugs are substances of natural or synthetic origin that can be used to alter someone's emotional state, perception, body functioning or behaviour. Many drugs have legitimate medical uses, and these and others are subject to "abuse" or "recreational use". Many of these substances are subject to national and international control, and therefore the detection, identification and quantification of these substances is an important aspect of forensic science 
The profiling of drugs can be very useful to the police. Drug profiling provides law enforcement agencies with physical and chemical information that may assist in identifying and disrupting drug trafficking organisations. Material from different seizures can be classified into groups of related samples. Consequently, and most useful for law enforcement authorities is when specific links for instance between suppliers and users can be established, drug distribution patterns, and networks can be built up along with the source. When detailed chemical analysis is completed it provides information which when compared to historical data allows the investigators to determine the geographic location of the cultivated drug heroin. When combined with physical evidence this information may also be used to help establish links between different seizures of illicit drugs [6, 13].
Law enforcement authorities normally require evidence to link users and drugs dealers; or information on local network. Forensic laboratories are then asked to determine whether samples of seized drugs are related by identifying similarities and differences between drug samples, the information generated by drug characterisation studies can be used to help law enforcement answer the following questions: are two or more drug samples connected? Does this relationship provide a link between, for example, a drug dealer and a user? Does the relationship between samples provide any useful information relating to local, national, regional or international drug supply and distribution networks or any information as to the extent of such networks? Where does the sample come from (e.g., geographic origin, laboratory source)? What is the method of clandestine drug production? Which specific chemicals are employed in the manufacturing process [2, 13].
Based on the type of drug sample investigated, the information generated through drug characterisation studies may be used to identify from where, how, and to what extent the drug has been distributed. It may be used to provide background intelligence on the number of sources of drugs, whether those sources are within a country or internationally based, and on points of drug distribution and drug distribution networks. Information from drug characterization studies may also be used to estimate how long a particular laboratory has been operating, and to assess the scale and output of a drug operation. Close cooperation between laboratory and law enforcement personnel is essential to maximize the operational value of drug characterization studies for law enforcement investigative work [6, 13].
In the profiling of the drug Heroin the following analytical techniques can be used, Gas chromatography (GC), liquid chromatography (LC), thin layer chromatography (TLC), High performance liquid chromatography (HPLC), inductively coupled plasma-mass spectrometry (ICP-MS), Ultraviolet-visible (UV-Vis) spectroscopy UV-Vis Spectroscopy, and capillary GC-FID [10,15].
Gas chromatography (GC) is an analytical tool frequently used in impurity profiling and it can also result in hydrolysis of heroin and/or the trans-etherification of co-injection compounds, GC analysis of heroin without the use of a derivatization step will result in the formation of three injection port artefacts. An injection of a heroin sample, in the absence of a derivatization step, will nearly always result in the production of some quantity. GC does require the compound to be thermally stable, volatile, and exhibit good chromatographic qualities. GC provides a means of separating the components of a complex mixture but the technique can definitively identify any component [7, 14].
In GC analysis, the system can be coupled to a mass spectrometer and a mass fragmentation pattern produced for each compound, which can be used to identify the compound together with the chromatographic data. GC-FID is often used in drug analysis but increasingly routine is the use of GC-MS. In this case the GC is interfaced with a mass spectrometer detector (MSD). This can be either in place of a conventional detection system such as an FID or in tandem with an existing detector. When using an MSD the carrier gas is generally helium, which has a low molecular weight .
Liquid Chromatography (LC) is a technique used commonly to identify and quantify drugs of abuse. The technique has a number of advantages and disadvantages specific to drug analysis. Advantages: it is nondestructive and samples can be recovered if required; the analyte does not need to be volatile; the sample generally does not require pretreatment such as chemical derivatization; the analysis can be automated; and quantification can be achieved without the necessity of an internal standard the analyte needs to have properties which can be detected in a liquid stream; in most cases a UV or diode array detector and so the analyte needs to possess chromophores; the sample needs to be soluble in a wide range of solvents; quantification can be slow; and large volume of solvents are used [9, 14].
High-performance liquid chromatography has probably overtaken GC in popularity for drugs determination and can provide a high degree of edibility with reduced risk of compound degradation during analysis. HPLC is suitable for screening and quantitation of most drugs and the running costs are usually modest .
Thin-layer chromatography methods provide a Single system which will detect a wide range of Drugs including heroin. Generally, TLC has poor sensitivity unless large volumes of sample are extracted, has low specificity, is slow and cumbersome, requires considerable time to learn the skill of interpreting the chromatograms, and cannot produce a quantitative answer. Some of these limitations have been partially overcome by the use of `high-performance' TLC (HPTLC) plates, separation on twin systems, use of more than one locating agent for one group of drugs or the application of complex locating agents which produce uorescent derivatives .
The analysis of trace elements using inductively coupled plasma-mass spectrometry (ICP-MS) has also been employed for sample comparison studies. ICP-MS has emerged as a major and powerful technique in the area of elemental analysis. It offers extremely low detection limits which range from sub parts per billion (ppb) to sub parts per trillion. In addition, it is a good technique used for the classification and the comparison of heroin samples. Also, the simple nature of the mass spectra of the elements makes this technique a quick tool for automated qualitative, semi quantitative, and quantitative elemental analysis .
FTIR is an extremely useful technique for confirming the identity of pure compounds. The technique is based upon the identification of functional groups within molecules where such groups vibrate (either through stretching or bending in various ways) when irradiated with specific wavelengths of light. These vibrations and their intensity (% transmission) are plotted against the frequency of light (cm_1) to which the sample is exposed to produce an FTIR spectrum. Portions of the FTIR spectrum are unique to the compound under test (this is called the fingerprint region). Unfortunately, because the majority of seized samples are mixtures of compounds, FTIR has limited practical use in the analysis of street samples of drugs of abuse. However, it does have the advantages of being nondestructive and not requiring derivatization .
Ultraviolet-visible (UV-Vis) spectroscopy UV-Visspectroscopy, like FTIR, is a technique which is useful in the identification of pure drug compounds. Different compounds contain chromophores, which will absorb specific wavelengths of UV or visible light. The technique obeys the Beer-Lambert law and as such the absorption of spectra generated at given wavelengths contains the added advantage of being directly related to the concentration of the sample. Normally UV and UV-Vis spectra are recorded at high and low pH and the results of both for the sample under question compared with known standards. UV-Vis is a cheap and easy technique, which allows sample recovery and good discrimination between pure compounds without the need for derivatization. It has less application for street samples involving complex mixtures 
From the above overview it should be clear that the profiling of drugs is very important to law enforcement. Profiling aids the law authorities with physical and chemical information necessary for the identification and characterisation of seized drugs. It is also clear that not all analytical techniques can be used to analyse the drug heroin. GC and LC are widely used techniques for the analysis of heroin.