it is to be understood that both the foregoing general description and the following description are exemplary and explanatory only and are not restrictive of the methods and devices described herein . in this application , the use of the singular includes the plural unless specifically state otherwise . also , the use of “ or ” means “ and / or ” unless state otherwise . similarly , “ comprise ,” “ comprises ,” “ comprising ,” “ include ,” “ includes ,” “ including ,” “ has ,” “ have ,” and “ having ” are not intended to be limiting . broadly stated , embodiments of the present invention provide analytical methods , instruments , and devices that address the shortcomings addressed above . the present invention provides a device , system , and associated methods that will actively or passively sample a material ( solid , liquid or gas ) by heating the sample , volatilizing it into the gas phase and directing it onto the surface of a substrate . the substrate is composed of a material ( either a solid , or a liquid - coated solid ) that has both high surface area and an active surface with excellent adsorptive properties . these properties can be tailored for retention of specific components or provide for broad adsorption of materials with general chemical properties . accordingly , the invention provides methods for sampling and analysis of samples to determine the chemical compounds thereof at low concentrations . the invention also describes instrumentation for the chemical analysis of materials adsorbed onto this substrate , whether that analysis is directly coupled to the sampling step , or removed in distance and in time from the sampling event . a sample tracking interface is provided using a method for reading sample identification information present in a first region of the encoded physical medium and then correlating the measured information with the sample identification information has been encoded therein . according to one embodiment , the information may be encoded according to a spatial encoding scheme , a bar code scheme , or a combination thereof . in one embodiment , the invention provides a method for detecting an analyte contained in a solid comprising the steps of heating the solid , directing a gas evolved from such heated solid comprising single or multiple chemical analyte ( s ) onto the surface of an adsorptive substrate ( particularly a “ target substrate ,” as defined herein ) in a sealed gas fluidic system for a period of time sufficient for the analyte to be adsorbed onto the surface ; and then analyzing the analyte . the analyte can be analyzed directly , for example , by contacting said target substrate with a sensor , and quantitatively and / or qualitatively evaluating the chemical composition of the analyte ( s ) on said substrate by the response of the sensor . in another embodiment , the target substrate thus obtained can be removed from the sampling instrument and placed in a suitable container that preserves the composition of the analyte within the target substrate , then shipped to a laboratory that contains appropriate instrumentation for chemical analysis . once there , the analyte ( s ) contained within the target substrate can be analyzed with conventional analytical instrumentation commonly used for chemical separations ( including gas chromatography ( gc ), high performance liquid chromatography ( hplc ), thin layer chromatography ( tlc ) or any of a variety of other methods used for chemical separations ) and these methods can be coupled with appropriate detection methods ( such as flame ionization detection , mass spectrometry , uv or visible light absorbance , infrared or neat infrared absorbance spectroscopy , or other related methods ). such analysis can be done directly ( for example , by placing the target substrate in the appropriate analytical instrument and performing the analysis ) or after extraction , where the target substrate is placed in a minimum volume of an appropriate solvent , and the analyte ( s ) are solubilized in the solvent . the resulting solution can then be used as the sample matrix for chemical analysis ( for example , the solution can be injected into a gc - ms or an hplc - uv absorbance detector ). in one aspect of the present invention , an apparatus for creating volatile components of a substance is disclosed . the apparatus comprises in combination a power source , a heater , a pump sufficient to create a gas flow , a temperature sensor , time and temperature control , a source material holder for holding the sample substance which is connected via inert tubing to a second receptacle for holding a target substrate that receives the vapor that results from the release of volatile components created by heating the sample and releasing volatile elements in a sealed gas fluidic system . the pump may create positive pressure at the sample source sufficient to push the evolved gas through the target substrate , or it may be a vacuum pump that creates a negative pressure at the target substrate , such that the evolved gas is “ sucked ” from the sample chamber thru the target substrate without releasing the gas to ambient atmosphere . the temperature sensor may be a thermocouple or resistance temperature detector ( rtd ) or other device suitable for monitoring temperature . the heater may be a ceramic uf heater , simply resistive heating tape wrapped around the sample container , or other suitable heating device . the airflow may be between 0 . 1 and 100 ml / min . the apparatus is not meant to release volatile elements into the ambient air without prior removal of volatile components generated during heating . also , the time and temperature controllers may produce a variable heat according to the specific substance being volatized in said apparatus . the apparatus may further comprise an information input / output device in communication with the power supply that displays the relevant parameters and allows for adjustment of said parameters by controlling relevant components within the apparatus . it should be understood that the information input / output device may be in communication in a multitude of ways including wireless and fiber optic communication . information may be manually inputted or programmed to be controlled automatically by the equipment into the information input / output device which in turn electrically communicates with the power , heater and pumps to adjust the temperature , flow rate and duration of the sampling process within said apparatus for a specified time . the time elapsed , temperature , and other desired information may be displayed on a display such as an lcd display . also , an information retrieval and delivery means in electrical , optical or wireless communication with said device may be used . this may be a usb , firewire , ethernet , wireless ethernet , ilink interface , nv interface , telephone cable interface , parallel interface , fiber optics , serial interface or other communication method connected to the apparatus and an information source ( e . g . computer ). the information retrieval and delivery means may be a disk contained within the apparatus , or it may be transmitted via the aforementioned communication protocols to an external information source . the temperature provided by the heater means is preferably between 0 ° c . and 300 ° c . the present invention improves the sample tracking interface by providing a method for interfacing via an encoded physical medium having a region wherein information has been encoded . the interface method includes reading sample identification information present in a first region of the encoded physical medium and then correlating the measured information with the sample identification information has been encoded therein . according to one embodiment , the information may be encoded according to a spatial encoding scheme , a bar code scheme , or a combination thereof . the present invention also teaches that when it is determined that the marker is present in the first region , that certain encoded information is translated into certain decoded information including a function to be performed by the computer system . the function to be performed by the computer system may include , among other things , providing a link to a webpage containing sample analysis information . the certain decoded information could also include a uniform resource locator ( url ) and the function may involve the computer system accessing and / or displaying an internet web page to which the url directs . the present invention further improves upon the sample tracking interface by teaching a method for generating an encoded physical medium having a region with encoded content . the method requires receiving content that is to be encoded into a desired location on the encoded physical medium , encoding the content according to a particular encoding scheme suitable for application onto the encoded physical medium , and inserting the encoded content together with a marker into a corresponding desired location within a representation of the encoded physical medium . the marker indicates that the content is encoded within the corresponding desired location , thereby enabling a subsequently engaged sensor to determine the existence of the content . once the representation is created , the present invention further teaches that the encoded physical medium may be generated from the representation . the present invention further teaches maintaining a database tracking the results of the user engaging the sensor with a plurality of samples , including the determination of multiple chemical components within a given sample . the database could then be used later to determine whether a specific condition ( i . e ., cannabinoid content exists within a given range ) has been satisfied . in turn , a specified action could be specified by the computer system ( i . e ., satisfy quality control release criteria ). one separate embodiment of the present invention teaches a computer interface between the sample , a user and a computer system using an encoded physical medium . the encoded physical medium is suitable for having at least one region wherein information has been encoded . the computer interface includes a sensor operable for measuring information present on the encoded physical medium , and a first device coupled to the sensor and responsive to determine whether information measured by the sensor includes a marker indicating that certain encoded information is present in the measured information . in a related embodiment , the computer interface includes a second device responsive to the first device such that when the first device determines the presence of the specified content , the second device is operable to decode the certain encoded information present in the measured information . in yet another related embodiment , the computer interface also has a transmitter device operable to transmit the certain decoded information to the computer system . according to another embodiment , an apparatus for releasing volatile elements of a substance in a sealed gas fluidic system is disclosed comprising in combination a power source in electrical communication with a heater and a pump , a thermocouple for sensing temperature , an information retrieval and delivery means in electrical communication with the power source , a time and temperature control device that adjusts the heat produced by the heater means and length of time heat is produced , information output means in electrical communication with the power means that displays the temperature and time , a source material holder for holding the substance connected via inert tubing to a target substrate holder for holding the target substrate . the time and temperature control means produces a variable heat according to the specific substance being volatized in a sealed gas fluidic system in the apparatus . the heat provided by the heater means is preferably between 0 ° c . and 300 ° c . and the gas flow between 0 . 1 and 100 ml / min . the heater can be energized at a defined rate , so as to create a programmed thermal cycle . this programmed thermal cycle allows the gradual heating of the sample , so that analytes with lower boiling points are volatilized first and removed from the sample before the heater produces temperatures that could decompose those materials . the heating is continued to volatilize additional higher boiling components and all those analytes are swept to the target substrate in a sealed gas fluidic system and adsorbed . in this way , a range of analytes of different boiling points can be effectively transferred to the target substrate without inducing thermal decomposition of the lower boiling materials . the composition of the target substrate can be varied to alter the selectivity of the adsorption process . the selectivity of adsorption is determined by the chemical composition of the target substrate material , and as a general rule , the doctrine , “ like dissolves like ,” is applied . for example , if the target analyte is composed of hydrophobic material , then a hydrophobic target material is selected , since it is likely to adsorb the analyte more strongly . similarly , if the analyte is hydrophilic , then a hydrophilic target material is selected . if the sample contains a variety of different chemicals with different solubilities , then the target substrate can comprise a combination of materials to adsorb the analytes . alternatively , the chemical composition of the target substrate can be altered by adding a thin film , or stationary phase to the surface of the substrate . as conventionally used in many chromatographic techniques , the stationary phase can consist of almost any material that can be deposited as a thin film and that forms a stable layer . examples of non - polar stationary phases include hp - 1 , hp - 5 as well as db - 1 and db - 5 , while other examples of stationary phases include hydrophilic or hygroscopic materials , e . g . based on cellulose , modified cellulose such as cellulose nitrate or cellulose acetate , hydroxyalkylated cellulose , or modified and unmodified cellulose crosslinked with substances such as epichlorhydrin . also suitable are glass fiber matrices and matrices consisting of polyester . these materials can either be used solely or in combination with other compound materials with a hydrophilic portion in the carrier matrix prevailing . in a preferred manner , the target substrate materials are structured so as to form particles ( e . g . pearl - like , see dd - a296 005 ) or fibers , such as filter papers on cellulose basis ( ep - a 374684 , ep - a 0470565 ). other materials used for the construction of the target substrate are described in ep - a 0 374 684 , ep - a 0 353 570 and ep - a 353 501 . the first carrier matrix must be gas - permeable to allow suitable animals with the corresponding immunogen . the enrichment of the immunologically active substance from the gas phase . for pressure gradients above the adsorber ( 200 - 500 mbar ) which are technically easy to implement , the gas permeabilities advantageously range between 1 ml / min and 100 l / min , preferably between 10 ml / min and 100 ml / min . in another embodiment , the target substrate &# 39 ; s chemical composition can be altered through reaction with specific binding components . biosensors making use of the principle of an immunological reaction between the analyte and binding partners contained in the biosensor would be potentially suitable for such tasks due to the high selectivity and specificity of the immunological reactions . a biosensor of this kind has been described by ngen - ngwainbi [ 49 ]. in this reference , an antibody to a cocaine metabolite ( benzoylecgonine ) as a reactive component of the sensor is used as a piezo transducer with a resonance frequency of 9 mhz . the antibody is immobilized through physical adsorption on the surface of the sensor . the lower detection limit is at 0 . 5 ppb corresponding to 2 × 10 − 11 mol / l in gas phase ( for cocaine and cocaine - hcl ). the invention also includes devices and instruments for use in the methods of the invention . for example , the invention includes a device for active sampling of a gas and directing the same gas onto a target substrate comprising a gas conduit having a sample port and a sealed gas fluidic system ; the sample port is fluidly connected to a target holder containing a target substrate , wherein the sample port is capable of directing a gas from the sample chamber onto a target substrate ; and a pump for introducing the gas through the sample port and moving the gas through the target holder such that the analyte can adsorb onto the target substrate in a sealed gas fluidic system . in another embodiment , the chemical composition of the analyte adsorbed onto the test substrate is determined by placing the test substrate in contact with an electrochemical sensor capable of sensing the desired analyte . the electrochemical sensor can monitor the presence of the phenolic molecule by direct oxidation of the phenol , for example , as shown for the electrochemical oxidation of phenol on a metal oxide electrode [ 50 ]. alternatively , the electrochemical sensor can consist of a carbon electrode modified with reagents that emulate the gibbs reaction . the present invention modifies or builds on the known gibbs reaction by electrochemically oxidizing a p - aminophenol ( pap ) to form a benzoquinone monoamine ( for example , a dichloro - or diphenyl - benzoquinone monoamine ), which then reacts with the substituted phenol compound of interest , as in the classical gibbs reaction . monitoring the reduction of an oxidized pap provides an indirect method of detecting phenols and phenolic compounds , or example phenol , 4 - phenoxyphenol , methylphenol ( para and meta ), nitrophenol , cannabinoids ( e . g . tetrahydrocannabinol ) and catechins ( e . g . egcg or ecg ). the methodology according to the present invention is attractive since it avoids the direct oxidation of the phenol , which can lead to electrode passivation . the pap may be present in the electrolyte and / or on the surface or in the bulk of the working electrode material . in one embodiment of the invention there is provided an electrochemical sensor for the detection of a phenol - containing molecule , which comprises a first compound , a working electrode and an electrolyte in contact with the working electrode , wherein the first compound operatively undergoes a redox reaction at the working electrode to form a second compound which operatively reacts in situ with the phenol , wherein said redox reaction has a detectable redox couple and wherein the sensor is adapted to determine the electrochemical response of the working electrode to the consumption of said second compound on reaction with the phenol . in another embodiment of the invention there is provided a method of sensing a phenol - containing molecule in a sample , comprising : ( a ) oxidizing a first compound at the working electrode of an electrochemical sensor to form a second compound which is operatively reactive with the phenol - containing molecule ; ( b ) contacting the phenol - containing molecule with the second compound in the presence of an electrolyte , such that the second compound reacts with the phenol - containing molecule ; and ( c ) determining the electrochemical response of the working electrode to the consumption of the second compound on reaction with the phenol - containing molecule . in the present invention , phenol - containing molecules can be detected indirectly . a number of electrochemical biosensors have been developed for the monitoring of phenols in aqueous systems . laccase , catechol oxidase , and tyrosinase have been used as biosensitive part of sensors in combination with other modifiers like carbon nanotubes ( cnt ), magnetic core - shell ( fe 3 o 4 — sio 2 ) nanoparticles , and polypyrrole . this approach leads to improvement of determination analytical selectivity and sensitivity [ 50 ]. in particular , the present invention involves the use of a compound which operatively undergoes a redox reaction at the working electrode , wherein the reaction has a detectable redox couple and wherein the product of said reaction operatively reacts in situ with the phenol - containing molecule . the electro - chemical response of the working electrode to the consumption of the said compound on reaction with the phenol - containing molecule is then determined . the phenol - containing molecule may be contacted with the compound prior to , contemporaneously with or subsequent to the oxidation of the compound , but is typically admitted subsequent thereto . in another embodiment of the invention , the choice of suitable sensor arrangement and materials is important when considering the moiety to be sensed , temperature range and electrochemical method to be used . amperometric sensors have been found to enable low cost of components , small size , and lower power consumption than other types of sensor , and are ideal for use in portable analysis systems . in the present invention , amperometric sensing methodology is typically employed . the working electrode may be a screen printed electrode , a metallic electrode , a metal nitride , a semiconductor , an edge plane pyrolytic graphite electrode , a basal plane pyrolytic graphite electrode , a gold electrode , a glassy carbon electrode , a boron doped diamond electrode , or a highly ordered pyrolytic graphite electrode . the working electrode may be a microelectrode or a macroelectrode . determination of the electrochemical response of the working electrode may comprise measuring the current flow between the working electrode and a counter electrode to determine the amount of phenol or phenolic compound . it is particularly preferred that the working electrode is operatively maintained at a constant voltage . in one embodiment , the current is measured using linear sweep or cyclic voltammetry . in another embodiment , said current is measured using square wave voltammetry . in an alternative embodiment , the current is measured using a pulsed voltammetry technique , in particular differential pulse voltammetry . sampling procedures to determined cannabinoids in hemp products for by means of gc - ms sample preparation , extraction and gas chromatographic separation conditions were derived from a literature reference [ 51 ]. these are summarized below : cannabidiol ( cbd ), cannabinol ( cbn ), δ9 - tetrahydrocannabinol ( thc ), and δ9 - tetrahydrocannabinol - d3 ( thc - d3 ) were purchased from promochem ( wesel , germany ). n - methyl - n - trimethylsilyltrifluoroacetamide ( mstfa ) was obtained from macherey - nagel ( duren , germany ). a spme device for an autosampler with a replaceable 100 - μm polydimethylsiloxane ( pdms ) fiber was obtained from supelco ( deisenhofen , germany ). the spme fiber was conditioned at 250 ° c . for one hour in the injection port of the gas chromatograph , according to the supplier &# 39 ; s instructions . chemicals were purchased from merck ( darmstadt , germany ). gc - ms analyses were carried out on a hp 6890 series plus gas chromatograph coupled to a 5973n mass - selective detector ( agilent ) and an autosampler . data acquisition and analysis were performed using standard software supplied by the manufacturer ( agilent chemstation ). substances were separated on a fused silica capillary column ( hp - 5ms , 30 m × 0 . 25 mm i . d ., film thickness 0 . 25 μm ). temperature program : 160 ° c . hold for 1 min , 15 ° min − 1 to 190 ° c ., hold for 1 min , 5 ° min − 1 to 250 ° c ., hold for 1 min , 20 ° min − 1 to 300 ° c ., hold for 2 min . the injection port , ion source , quadrupole , and interface temperatures were 250 ° c ., 230 ° c ., 150 ° c . and 280 ° c ., respectively . splitless injection mode was used and helium , with a flow rate of 1 . 0 ml min − 1 , was used as carrier gas . a diverse range of commercially available hemp food products were purchased from esoteric and nature stores and via the internet . all solid samples were blended and homogenized in a standard mixer . liquid samples were homogenized by shaking . hemp tea infusions were prepared by pouring 100 ml boiling water on 1 . 5 g tea . after 15 min , the infusion was filtered . for hs - spme extraction , approximately 50 mg ( tea ), 400 mg ( chocolate , snack bar , thin slices ), 100 mg ( seed , flour , fruit bar , nibbles ), 1000 mg ( pastilles ), 100 μl ( oil ), 500 μl ( lemonade , beer ), or 1000 μl ( tea infusion , shampoo ) sample were placed directly in a 10 - ml headspace vial in the presence of 1 ml naoh ( 1 mol l − 1 ), 0 . 5 g of sodium carbonate , and 100 μl aqueous internal standard solution ( 200 ng ml − 1 thc - d3 ). for on - coating derivatization , a separate vial containing 25 μl derivatization reagents ( mstfa for silylation ) was prepared for each sample . the vials were sealed using a silicone / ptfa septum and a magnetic cap . the sample vial was shaken for 5 min at 90 ° c . in the agitator of the autosampler ( 650 rpm , agitator on time 0 : 05 min , agitator off time 0 : 02 min ). for absorption , the needle of the spme device containing the extraction fiber was inserted through the septum of the vial and the fiber was exposed to the headspace in the vial for 25 min . then for derivatization the fiber was exposed for 8 min at 90 ° c . in a second vial containing 25 μl mstfa . finally , the spme fiber with the absorbed and derivatized compounds was introduced into the injection port of the gc - ms for 5 min to accomplish complete desorption of the analytes . for liquid - liquid extraction , 100 μl of the internal standard solution and 5 ml 9 : 1 ( v / v ) n - hexane - ethyl acetate were added to the same amount of sample ; the mixture was homogenized for 15 min under ultrasonication and centrifuged for 5 min . the organic layer was separated and the lower layer was extracted another two times with 5 ml n - hexane - ethyl acetate . alternatively , the oil samples were extracted three times with methanol . the combined organic extract was evaporated under nitrogen . the dried samples were derivatized with a mixture of 50 μl mstfa , 20 μl pyridine , and 130 μl isooctane under incubation at 90 ° c . for 15 min . after transfer to gc injection vials 1 μl was injected for gc - ms analysis . to examine the effect of the matrix on the spme extraction process , multiple portions from 25 to 200 mg of hemp tea , hemp chocolate , and hemp oil were analyzed . for validation of the method , spiked samples were prepared , using olive oil , milk chocolate , and green tea as blank matrices . precision and accuracy was determined by repeated analysis of the spiked samples . the linearity of the calibration plots was evaluated between 0 . 1 and 4 mg kg − 1 ( related to 100 mg weighed portion ). for determination of the limits of detection ( lod ) and quantitation ( loq ), separate calibration curves in the range of the lod ( 0 . 005 - 0 . 5 mg kg − 1 ) were established . for purposes of comparison all samples were analyzed using hs - spme and lle , and comparison of representative chromatograms from gc - ms analysis of identical hemp tea samples using lle and hs - spme reveals the superiority of hs - spme . in the lle chromatogram several large matrix peaks elute in the retention - time range of the analytes , whereas when hs - spme was used distinct peaks were acquired for all compounds with slight or little matrix interference . this is in good agreement between levels of cannabinoids determined in food samples by hs - spme and lle [ 52 ]. the linearity of the correlation between hs - spme and lle was significant , with correlation coefficients of 0 . 992 ( thc ), 0 . 974 ( cbd ), and 0 . 985 ( cbn ). the slope and intercept of the regression lines show there is no constant or proportional difference between the two procedures . the limits of detection achieved by hs - spme were comparable with those of already published methods applying conventional techniques ; some were even better [ 52 ]. lachenmeier et . al . reported that when thirty authentic samples were analyzed by means of hsspme with gc - ms , no matrix interferences were observed . headspace extraction in combination with spme separates the semi - volatile cannabinoids from non - volatile compounds . peak purity and selectivity are ensured . interfering peaks , often observed in gc - ms analyses for thc after conventional extraction and silylation , are excluded , because of lower matrix contamination [ 52 ]. recoveries of the analytes , as determined by both hs - spme and lle , depend on their distribution coefficients in the equilibrium of the extraction process for both procedures [ 52 ]. lle involves homogenization of the two liquid phases to accelerate adjustment of the equilibrium concentrations . however , it is not possible to homogenize the phases in hs - spme ( since it is a two phase system ), therefore the transfer of the molecules from the liquid to the gas phase is rate determining . matrix properties such as viscosity or lipophilicity therefore affect the headspace procedure to a large extent , so the speed of diffusion of the analytes in the matrix is crucial . extraction recoveries for simpler matrices ( e . g . tea ) were found to be proportional to the amount of sample . complex lipid - and protein - containing matrices , for example chocolate , caused significant matrix retention and lower recoveries [ 52 ]. suppression of hs - spme extraction recovery by lipid material has previously been reported , and the only way this could be mitigated was through the use of alkaline hydrolysis to saponify the lipids . they found that this resulted in low extraction yields , but it was possible to determine the cannabinoids reproducibly and automatically by using a versatile and programmable autosampler . although the matrix varies considerably for the foods studied , the sensitivity of the procedure was sufficient to determine whether the thc content of the foods was within the guidance values . sample preparation , extraction and gas chromatographic separation conditions were derived from a literature reference [ 41 ]. these are summarized below : all chemicals were of analytical grade and used as received without any further purification . these were 49 - tetrahydrocannabinol ( hplc grade , & gt ; 90 %, ethanol solution ), 2 , 6 - dichloro - p - aminophenol , phenol , and 4 - phenylphenol , (& gt ; 98 %, sigma - aldrich ). solutions were prepared with deionized water of resistivity not less than 18 . 2 m ohm cm − 1 ( millipore water systems ). voltammetric measurements were carried out using a ch - 650a potentiostat ( ch instruments , austin , tex .) with a three electrode configuration . glassy carbon electrodes ( ch instruments , austin , tex .) or carbon paste electrodes were used as working electrodes . carbon paste was prepared from a mixture of 0 . 35 gram graphite and 0 . 1 gram nujol oil , mixed by grinding in a mortar / pestle for 10 - 15 minutes . the carbon paste mixture was packed into a teflon cylinder electrode case and contacted with a copper wire ( ch instruments , austin , tex .). the counter electrode was a bright platinum wire , with a saturated calomel or ag / ag + reference electrode completing the circuit . the glassy carbon electrodes were polished on silica lapping compounds ( bdh ) of decreasing sizes ( 0 . 1 to 0 . 05 um ) on soft lapping pads , then rinsed with di water immediately prior to use . all experiments were typically conducted at 20 ± 2 ° c . before commencing experiments , nitrogen was used for deaeration of solutions . stock solutions of the substituted phenols were prepared by dissolving the required substituted phenol in methanol . initial voltammetric characterization of 4 - amino - 2 , 6 - dichlorophenol ( pap ). first , the voltammetric response of an glassy carbon electrode in ph 10 borate buffer solution ( 50 mm ) containing 1 mm 4 - amino - 2 , 6 - dichlorophenol ( pap ) was demonstrated . the corresponding voltammetry is shown in fig4 a . the oxidation peak is observed at + 0 . 074 v ( vs . ag / ag + ) with a corresponding reduction peak at + 0 . 010v ( vs . ag / ag + ) which is due to the redox system of p - aminophenol - quinoneimine ( pap - qi ), fig3 . the response of pap to increasing additions of phenol was measured using square - wave voltammetry ( sw - voltammetry ) at a carbon electrode to try to increase the sensitivity of the protocol . sw - voltammetry was used because this technique has an increased sensitivity over linear sweep ( or cyclic voltammetry ), due to the fact that the former is a measure of the net current , which is the difference between the forward and reverse current pulses and also using sw - voltammetry , only one peak is observed , allowing one to easily monitor the reduction of the voltammetry peak on additions of the phenol compound . initially , the sw parameters were optimized . using a ph 10 buffer solution containing 1 mm pap , the frequency and step potential were each in turn changed to find the optimum peak height ; this was consequently found to occur when the frequency was 8 hz , the step potential 4 mv and the amplitude 25 mv . using these parameters the sw voltammetric response from an glassy carbon electrode was obtained in a ph 10 buffer solution containing 1 mm pap . the voltammogram was cycled until the peak had stabilized , which is typically after two cycles , after which phenol additions were made to the solution . as depicted in fig5 , the well - defined sw voltammetric response was found to decrease with added phenol concentrations . analysis of the peak current vs . added phenol concentration was found to be highly linear from 0 to 400 μm . from this , a limit of detection ( 3σ ) was found to be ˜ 10 μm . note that in employing sw voltammetry , which involves holding the potential at + 0 . 4 v for 4 s , the direct oxidation of the phenol ( or phenol derivatives ) is completely avoided , such that any possible electrode passivation is circumvented . this explains the slightly less favorable regression data seen using cyclic voltammetry ( in comparison to sw - voltammetry ), where the potential is swept into the region where phenol oxidation occurs . thus , given the simplicity and reduced possibility of electrode fouling from using the sw - voltammetry technique , this protocol was used throughout the following work . a control experiment was performed where identical volume sized additions were made of either water or ethanol to a ph 10 borate buffer solution containing 1 mm pap without any phenol present . no significant reduction in the pap voltammetric peak was observed for both the water and ethanol additions . this indicates that neither dilution effects nor reaction with ethanol were responsible for the decrease in the voltammetric response of the pap as observed in fig5 ; thus , the latter is purely from the gibbs reaction of phenol with qi . above , we have shown a useful electrochemical methodology for the indirect determination of substituted phenol compounds . we now turn to exploring if this protocol is able to detect thc at carbon paste electrodes . the chemical structure of the latter is shown in fig1 , where it can be seen that it is effectively a phenol derivative which should undergo attack from the electrochemically produced dichloro - benzoquinone monoamine . the electrochemical response at a glassy carbon electrode for the electrochemical oxidation of 1 mm pap in a ph 10 borate buffer solution was established as shown in fig4 . additions of phenol were made over the range of 100 - 600 μm to the solution , with the observed response depicted in fig6 . as observed for phenol additions described above , the reduction peak has decreased with increasing phenol additions , indicating that the protocol works as an indirect methodology for the detection of thc , the active part of cannabis . we now turn to quantify this result with sw - voltammetry . using a 1 - mm pap solution in a ph 10 borate buffer solution , additional sw - voltammetric responses were obtained using carbon paste electrodes . the response of additions of phenol was explored . as depicted in fig7 , the voltammetric peak was found to decrease with increasing additions of phenol . analysis of the peak height vs . added phenol concentrations revealed linear parts of the calibration curve . from this a limit of detection ( 3σ ) was found to be 25 μm . while this limit of detection is not as low as previous analytical techniques ( such as hplc or gas chromatography as described in the introduction ), these cannot be easily adapted to hand - held ( portable ) devices . as indicated by the references cited , the detection of a variety of cannabinoid molecules should proceed in essentially the same manner . the phenolic part of the cannabinoid will undergo the same attack from the electrochemically produced dichloro - benzoquinone monoamine , and the concentration of the cannabinoid present can be inferred by the consumption of the electrochemically generated reagent . the strategy used for electrochemical detection can be selected from any of the widely known techniques , it was illustrated here with square wave voltammetry due to the convenience and availability of the instrumentation . similar results should be obtained with a wide variety of electroanalytical techniques , including cyclic voltammetry , linear sweep voltammetry , normal pulse voltammetry , differential pulse voltammetry , chronoamperometry , chronocoulometry , sinusoidal voltammetry , ac impedance and other related methods . the foregoing methods , devices and description are intended to be illustrative . in view of the teachings provided herein , other approaches will be evident to those of skill in the relevant art , and such approaches are intended to fall within the scope of the present invention .