Determination of methamphetamine in urine in situ using a methamphetamine-sensitive membrane electrode

Analytrca Chunrca Acta, 274 (1993) 59-63

59

Elsevler Science Pubhshers B V , Amsterdam

Determination of methamphetamine in urine in situ using a methamphetamine-sensitive membrane electrode IQyoyulu Watanabe and Kumo Okada Cwunal

Investrgatwn Laboratory, Okayama Prefectural Pokce Headquarters, To&a-cho,

Okayam

700 (Japan)

Takashl Katsu Faculty of Phamceutrcal

Sctences, Okayama Unwersuy, Tsushuna-naka, Okayama 700 (Japan)

(Received 5th September 1992, revised manuscript received 23rd October 1992)

A method for the determmatlon of methamphetamme m urme usmg a methamphetamme-sensltlve membrane electrode was developed No pretreatment of urme samples was required, which enabled methamphetamme excreted m the urme of drug addicts to be assayed sensltlvely and selectively The electrode was constructed by mcorporatmg sodmm tetralus[3,5-b~trdluoromethyl)phenyl&orate as the Ion exchanger and tncresyl phosphate as the membrane solvent m a poly$nnyl chloride) membrane matnx The detection hrmt for methamphetamme m urme was 10 PM The response charactenstlca were affected conslderably by changmg the membrane solvent and tncresyl phosphate was found to be the most smtable for the determmatlon of methamphetamme m urme Keywords Ion selective electrodes, Potentlometry, Membrane electrodes, Methamphetamme, Urme

Methamphetamme 1s known to stimulate central nervous system actlvlty, it has a slgmflcant potential for abuse and tolerance and its dependence-producing property leads to psycholo@cal dlsmtegratlon [l] In Japan, the use of this drug 1s regulated by the Stmmlant Drugs Control Act passed m 1951 Nevertheless, methamphetamme abuse 1s still endemic m Japan Therefore, the detection of methamphetamme m the urme of offenders, which 1s analysed most commonly by gas chromatography-mass spectrometry or mfrared spectrometry after extraction of methamphetamme from the urme with an orgamc solvent, followed by punficatlon by thm-layer chromatography [l], forms a large part of the workCorrespondence to T Katsu, Faculty of Pharmaceutical SCIences, Okayama Umvernty, Tsushlma-naka, Okayama 700 (Japan)

load of the Japanese Crnnmal Investlgatlon Laboratory m each prefecture A great deal of effort has been devoted to developmg and unprovmg techniques used to determme methamphetamme [1,21 The methods reported hltherto include spectrophotometry, spectrofluornnetry, chromatography, mass fragmentometry and rmmunoassay

WI We were interested m using an ion-selective electrode, which IS attractive for routme analyses, as compounds can be determmed easrly with no associated sample &our or turbldlty problems and hence the samples reqmre no pretreatment Considerable attention has been paid to the development and applrcatlon of drug-senatlve electrodes [3,4] The mltlal methamphetamme-sensltlve electrode developed was a coated-wire type and dmonylnaphthalenesulphomc acid was used as the ion exchanger [51 Selectlv@ data have

0003-2670/93/$06 00 8 1993 - Elsevler Science Publrshers B V All rights reserved

60

been evaluated for a few basic ammo compounds, but not for morgamc catlons (such as Na+ and K+) which are important when analysmg blologlcal samples More recently, Hassan and Elnemma [6] succeeded m constructing an amphetammeselective liquid-membrane electrode, based on the use of a neutral carrier, dlbenzo-18-crown-6 or dlbenzo-24-crown-8 The electrode showed a highly sensitive and selective response to amphetamine, which lacks the N-methyl group of methamphetamme Although the response of this electrode to methamphetamme has not been determined, it would be expected to be weak, because the specific mtelactlon between the host crown ether and guest amphetamine was the baSISof the electrode response [6] In this study, a methamphetamme-sensitive electrode was constructed by mcorporatmg sodium tetrakls[3,5-b~s(trdYluoromethyl)henyl]borate (NaTFPB) as the ion exchanger and tncresyl phosphate (TCP) as the membrane solvent mto a poly(vmy1 chloride) (PVC) membrane matrlx NaTF’PB was chosen because of its highly hpophlllc character and high stab&y [7] and TCP, which suffered no serious interference from ammes with high hpophlhatles, was found to be the most suitable for the determination of methamphetamme m urme This electrode enabled methamphetamme excreted m the urine of drug addicts to be determined m situ This appears to be the first attempt to determine a blologlcally active drug excreted m urine directly using an ion-selective electrode

EXPERIMENTAL

Electrode system The methamphetamme-sensitive membrane electrode was based on a PVC membrane [8,9] and its components were 05 mg of NaTFPB (Dojmdo), 60 ~1 of TCP (Tokyo Kasel) and 30 mg of PVC (degree of polymernatlon 1020) (Nacalal Tesque) The materials were dissolved m tetrahydrofuran, poured mto a flat Petn dish (30 mm diameter) and the solvent was allowed to evaporate at room temperature The resulting membrane was cut out and stuck to a PVC tube (4 mm

K Watanabe et al /Ad

Chm Acta 274 (1993) 59-63

o d ,3 mm 1 d ) usmg tetrahydrofuran as an adhesive Two other PVC membranes containing 2fluoro-2’-mtrodlphenyl ether (PNDPE) (Dojmdo) and dr(n-octyl) phthalate (DOP) (Tokyo Kasel) membrane solvents were prepared slmllarly Each PVC tube was filled with an mtemal solution of 10 mM methamphetamme hydrochlonde and the sensor membrane was condltloned overnight The electrochemical cell arrangement was Ag, AgCl/ internal solution/ sensor membrane/ sample solutlon/l M NH,NO, (salt bndge)/lO mM KCl/Ag, AgCl The em f between the silver/ silver chloride electrodes was measured with an appropriate field-effect transistor operational amplifier (input resistance > 1Ol2 a) and recorded The volume of sample solutron was 1 ml The selectlvlty coefficients of the electrodes were evaluated by the fixed-interference method [8,9] The detection lumt was defined as the mtersection point of the extrapolated hnear regions of the cahbratlon graph [8,9] Methamphetamme hydrochloride and ephedrine hydrochloride were purchased from Damlppon Selyaku and all the other chemicals were of analytical-reagent grade, unless stated otherwlse Gas chromatography Methamphetanune m urme was extracted with hexane, as described below, for determmatlon by conventional gas chromatography Urme (5 ml) was plpetted mto a test tube (10 ml), followed by add&on of hexane (2 ml), m which a known amount of the required internal standard compound had been dissolved, then one drop of 5 M NaOH was added to this mtiure to lead the methamphetamme mto the hexane layer The tube was capped, shaken and centrifuged at low speed and about 1 ~1 of the hexane layer was inJected directly into a gas chromatograph (Hewlett-Packard Model 5890) equipped with a DB-1 capillary column (J&W Saentlflc) The carrier gas was helium, the sphttmg ratio was ca 40 1, the flow-rate was 15 ml/mm and the mjectlon temperature was set at 300°C The column temperature was increased from 100 to 250°C at lO”C/mm and then held at 250°C for 5 mm The effluent passed mto a flame lomzatlon detector The ldentlflcatlon and quantlflcatlon of metham-

K Watanabe et al /Anal

Chm Acta 274 (1993) 59-63

61

phetanune were based on the retention tnne and peak area relative to those of the appropnate internal standard Two mtemal standards were used, hexadecane for the higher methamphetamme concentration range (> 5 x 10m5 M) and tndecane for the lower range (,< 5 x lo-’ M)

0

-50

s & w

RESULTS AND DISCUSSION

The effect of membrane solvents on the response of the electrode to methamphetamme m urme was studied first usmg NaTFPB as the ion exchanger Cahbratlon graphs were obtained by measuring known amounts of methamphetamme added to a urine sample from a normal donor and plotting the concentrations agamst the corresponding e m f values obtamed Qptcal results obtained with the three membrane solvents used, TCP, FNDPE and DOP, are shown m Fig 1 Of these, a wde range of linear responses and the lowest detection hmlt (10 PM) were obtamed with TCP Calibration graphs for these electrodes were also obtained for methamphetamme m blood serum and m a solution contammg 0 5 M MgCl, In the latter instance, a high concentration of MgCl, was added to adjust the ionic strength of the solution [9] The MgCl, salt was chosen because the response to magnesium 1s negligible, which 1s apparent from the selectWy coefficient of the electrode discussed later The detection lumt and the slope of the cahbratlon graph of each electrode under these three different condltlons are summarned m Table 1 The FNDPE-contammg electrode showed a wde range of responses to methamphetamme m serum

-100

-150

/ log[methamphetammel

(MI

Fu 1 Effect of membranesohrents on the electrode-response to methamphetamme m urme l = TCP, A = DOP, n = FNDPE

wth the lowest detection hmlt (5 PM), m contrast to the urme results, whereas DOP was mferlor to FNDPE and TCP for methamphetamme determmatlon m both serum and urme, although all the electrodes afforded comparable detection limits m 0 5 M MgCl, solution (l-2 FM) These results demonstrate that the choice of membrane solvent 1s unportant to ensure the lowest possible detection llrmt for each type of sample obtamed From the results of this study, the use of TCP 1s

TABLE 1 Electrode parameters Sample

Urine Serum 05MMgC1,’

FNDPE

TCP Slope (mV per decade)

DetectIon hnut (cLM)

Slope (mV per decade)

56 57 56

10 20 2

52 55 56

a Added to adjust the ionic strength of the solution

DOP Detectlou &MI

Slope (mV per decade)

Detection hmit (FM)

200 5 1

56 57 56

60 30 2

hm1t

K Watanabe et al /Ad

62 TABLE 2

appears to be the reason why FNDPE afforded the lowest detection hnut for methamphetamme m blood serum, m whch a high concentratlon of Na+ alone 1s notlceable TCP was used thereafter, as the prnnary aim of thus study was to determine the concentration of methamphetamme m the urine of drug addicts The response tnne of this electrode was less than 10 s when the concentration of methamphetamme was changed from 10 to 100 PM The pH dependence of the electrode with three different methamphetamme concentration levels IS shown m Fig 2 The pH of the solutron was changed by adding an appropriate amount of dilute hydrochlorlc acid or sodium hydroxide solution The ionic strength of the solution was adjusted by adding 0 5 M CaCl,, instead of 0 5 M MgCl,, because Mg(OH), 1s deposited at high pH values (pH > 9) [9] The electrode response was mdependent of pH over the pH range 3-8 The slgmflcant increase m the potential observed below pH 3 with the lowest concentration of methamphetamme used (1 x 10d5 M) was due to

This

Selectivity coefficients, log Kpp’ a Membrane solvent

Interfermg Ion(J)

Concentratlon (M)

Log K Pot

TCP

Mg2+ Ca2+ Na+ K+ H+ CH,NH; (CH&,N+

05 05 05 05 05 05 0 05 0005 00005

-55 -52 -43 -44 -31 -33 -21 -14 -19

05 05 05 05 05 05 00005 000005 00005

-51 -51 -51 -42 -49 -37 -09 07 -11

(C,H,),N+ Ephednne FNDPE

Chm Acta 274 (1993) 59-63

Mg*+ Ca*+ Na+ ;: CH,NH: (CH3&N+ (C2HS&N+ Ephednne

a z= Methamphetamme

and

J =

I,

mterfermg Ion

recommended for the determmatlon of methamphetamme m urine, whereas FNDPE IS the most suitable for its determmatlon m blood serum In order to establish the response charactenstics of TCP and FNDPE m more detail, the selectlvlty coefficients of both electrodes were also measured using the fixed-interference method The results, together with the concentrations of interfering ions used, are summarized m Table 2 The electrode made with TCP suffered no senous interference from quaternary ammes with high hpophlhcltles and also showed a sigmficantly high selectmty for ephedrine, which 1s structurally smular to methamphetamme Such a capacity of TCP to dlscrlmmate methamphetamme from various ammes 1s important, because electrode-sensltme ammes and their metabohtes, other than methamphetamme, may be excreted m urine snnultaneously A previous study [81has also demonstrated that a TCP-contammg membrane tends to respond to specific ammes, mdependently of the sequence of hpophlhcltles of amrnes Although TCP was superior to FNDPE for the recogmtlon of methamphetamme, it showed a higher response to Na+ than FNDPE

1 ii3M methamphetamme

t 2

I

I

4

I

1

t

6

I

8

I

I

10

PH Fig 2 Effect of pH on the response of the TCP-contammg electrode to methampbetamme

K Watanabe et al /Anal

63

Chzm Acia 274 (1993) 59-63

taneously by gas chromatography (Fig 3) The methamphetamme concentrations determmed by gas chromatography are shown on the abscissa and the correspondmg electrrcal potentials determined with the electrode are shown on the ordlnate The plots were virtually superimposable on the cahbratlon graph obtained with the TCP-contaming electrode, which 1s also shown This close correlation demonstrated clearly that methamphetamme m urine can be determined usmg this electrode No pretreatment of the urine samples 1s reqmred and, therefore, the determmatlon can be carried out m situ, offering a simple practical assay of methamphetamme excreted m urine This advantage should make a valuable contnbutlon not only m forensic chemistry but m various other fields requiring methamphetamme determmatlon

iog[methamphetammel

(M)

Fig 3 Plots of the methamphetamme concentration determmed by gas chromatography vs the electrical potential measured usmg the methamphetamme-sensltlve electrode Results for unne sample from 18 methamphetamme addxts (0) and the cahbratlon graph (0) of the electrode are shown

interference from H+ and the potential decrease above pH 8 was attributable to an increase m the concentration of unprotonated ammes, as the pK, of methamphetamme has been reported to be about 9 5 [lo] The pH independence m the range 4-9 was suitable for the deterrnmatlon of methamphetamme m urme, the normal pH range of which 1s 4 7-7 8 1111 Next, the electrode was used to determme the methamphetamme concentration m the urme of drug addicts It 1s known that a relatively large amount of methamphetamme 1s excreted m urine without bemg metabohzed [l] Urine samples from eighteen users arrested m Okayama prefecture were analysed usmg the TCP-contammg methamphetamme-sensitive electrode and slmul-

This work was supported by a Grant-m-Ad from the Shlmadzu Science Foundation

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