Determination of Five Abused Drugs in Nitrite-Adulterated Urine by Immunoassays and Gas Chromatography-Mass Spectrometry

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1 Detemination of Five Abused Dugs in Nitite-Adulteated Uine by Immunoassays and Gas Chomatogaphy-Mass Spectomety S.-C.J. Tsai 1, M.A. EISohly, T. Dubovsky t, B. Twaowska 1, J. Towt I, and S.J. Salamone 1 1Intenational Dug Monitoing Business Unit, Roche Diagnostic Systems, Inc., 18 US Highway, Someville, New Jesey 8876 and EISohly Laboatoies, Inc., 5 Industial Pak Dive, Oxfod, Mississippi 8655 [Abstact I The adulteation of uine specimens with nitite ion hasseen shown to mask the gas chomatogaphy-mass spectomety (GC-MS) confimation testing of maijuana use. This study was designed to futhe investigate the effect of nitite adulteation on the detection of five commonly abused dugs by immunoassay sceening and GC-MS analysis. The dugs tested ae cocaine metabolite (benzoylecgonine), mophine, 11-no-Ag-tetahydocannabinol- 9-caboxylic acid (THCCOOH), amphetamine, and phencyclidine. The immunoassays evaluated included the instument-based Abusceen ONLINE assays, the on-site Abusceen ONTRAK assays, and the one-step ONTRAK TESTCUP-5 assay. Multianalyte standads containing vaious levels of dugs wee used to test the influence of both potassium and sodium nitite. In the ONLINE immunoassays, the pesence of up to 1.M nitite in the multianalyte standads had no significant effect fo benzoylecgonine, mophine, and phencyclidine assays. With a high concentation of nitite, ONLINE became moe sensitive fo amphetamine (detected moe dug than what was expected) and less sensitive fo THCCOOH (detected less dug than what was expected). No effects of nitite wee obseved on the esults of the Abusceen ONTRAK assays. Similaly, no effects wee obseved on the absolute qualitative esults of the TESTCUP-5 when testing the nitite-adulteated standads. Howeve, the poduced intensities of the signals that indicate the negative test esults wee slightly loweed in the THC and phencyclidine assays. The pesence of 1.M of nitite did not show damatic intefeence with the GC-MS analysis of benzoylecgonine, mophine, amphetamine, and phencyclidine. In contast, nitite ion significantly intefeed with the detection of THCCOOH by GC-MS. The pesence of.m of nitite ion esulted in significant loss in the ecovey of THCCOOH and its intenal standad by GC-MS. The poblem of nitite adulteation could be alleviated by sodium bisulfite teatment even when the specimens wee spiked with 1.M of nitite ion. Although bisulflte teatment decomposed all nitite ions in the sample to ecove the emaining THCCOOH by GC-MS, the net ecovey of THCCOOH depended on uinay ph and time and conditions of sample stoage. The pesence of nitite concentations that might aise fom all possible natual souces, including micooganisms, pathological conditions, and medications, did not inteefee with the GC-MS analysis of THCCOOH. Intoduction Seveal suveys and studies to suppot the pemise that dugof-abuse testing effectively detes and detects dug abuse poblems have been published (1). Well-established in its ole in cubing and monitoing ciminal offendes (), dug testing also seves as an indispensable diagnostic aid and effectual teatment tool of dug abuse and addiction. Ove the last decade, employee dug testing has become a common business pactice in the Ameican wokplace (,). A study by the Ameican Management Association showed that the ate of positive dug-test esults among employees has dopped fom 8.1% in 1989 to 1.9% in 199 since the inception of the SAMHSA wokplace dugtesting pogam (5). As uine dug testing gains in populaity in both scheduled and andom tests in society, thee is a gowing numbe of new poducts and methods designed to defeat the test and mask dug use o abuse (6). A battey of commecial adulteants and household chemicals have been used fo the puposeful adulteation of uine (7-11). Most of the in vito adulteants wee used to skew the initial immunoassay dug sceening and hence bing about a false-negative esult, which in tun will avoid the gas chomatogaphic-mass spectometic (GC-MS) confimation test. The mechanisms o impact of these adulteants on seveal instument-based immunoassays have been well documented (7-11). Seveal laboatoies have ecently encounteed inceased incidences of specimens that sceened positive fo 11- no-a9-tetahydocannabinol-9-caboxylic acid (THCCOOH) by immunoassay but failed the GC-MS confimation test (1-15). Futhe investigations evealed that a new adulteant was pesented in these uine specimens (1). EISohly et al. (1) identified this adulteant, "Klea," as potassium nitite (KNO) and showed a pocedue to ovecome its intefeence in the GC-MS analysis of THCCOOH. Although it is not clea how widely Klea has been used fo uine adulteation, the poduct is still actively advetised on the intenet and in tade magazines with claims such as "undetectable uine puifie", "mask all foeign mateials fom the body", "a poven solution", o "the best poduct available if you ae not subject to supevised testing". Moeove, it was also not clea if nitite adulteation could 7 Repoduction (photocopying) of editoial content of this jounal is pohibited without publishe's pemission.

2 intefee with the detection of othe abused dugs besides maijuana. This study was conducted to investigate the effect of high concentations of nitites on the detection of five commonly abused dugs by immunoassay sceening and GC--MS analysis. In addition to evaluating the instument-based Abusceen ONLINE assays, we also examined the on-site Abusceen ONTRAK assays and the one-step, multianalyte ONTRAK TESTCUP-5 assay (16-19). Although most of the epots on uine adulteation wee on instument-based immunoassays, the study of adulteation on on-site dug tests ae impotant because thee has been an eve-inceasing application of on-site assays in wokplace dug testing (,1). Futhe, ecent immunochomatogaphicbased on-site assays such as ONTRAK TESTCUP do not equie sample manipulation and use the whole uine sample matix fo the testing (18). Thus the study of adulteant issues is especially impotant fo the on-site tests. It has been demonstated that the intefeence in the GC-MS confimation of maijuana use by up to.1m of nitite can be ovecome by a bisulfite-teatment step (1). The effect of bisulite teatment on uine specimens that wee adulteated with high concentation of nitite (1.M) was investigated in this study. Because nitite can be pesent in uine fom conditions such as uinay tact infection o medications (1,), the effect of low nitite concentations on the GC-MS analysis of THC- COOH was also examined. Expeimental Dugs and chemicals Benzoylecgonine-HCl, mophine sulfate, phencyclidine-hc1, amphetamine-hci, sodium nitite, and potassium nitite wee puchased fom Sigma (St. Louis, Mo). THCCOOH was obtained fom Reseach ~angle Institute (Chapel Hill, NC). Instumentation and eagents Abusceen ONLINE eagents and calibatos, Abusceen ONTRAK eagents, and ONTRAK TESTCUP wee obtained fom Roche DiagnosUc Systems, Inc. (Someville, N J). ONLINE assays wee pefomed on a COBAS MIRA analyze in a semi-quantitative mode accoding to the manufactue's instuctions (). Instument calibation is pefomed using the five-level Abusceen ONLINE Cannabinoids calibatos fo THCCOOH assay. A fou-point calibation cuve was geneated fo each of the othe fou assays based on the Abusceen ONLINE Calibation Pack (). ONLINE technology is based on the kinetic inteaction of micopaticles in a solution as measued by changes in light tansmission. The calibation cuves wee used to convet the esponse of the instument (optical densities measued fom the sample) to units of concentation. The qualitative ONTRAK assays and TESTCUP assay wee pefomed accoding to the manufactue's instuctions (). The CHEMSTRIP uine test stips wee puchased fom Boehinge Mannheim Cop. (Indianapolis, IN). Uine contols Contols wee pepaed in pooled, filteed, nomal human uine containing.9% sodium azide. The uine pool was detemined to be dug fee fo the five assays examined in this study by both the Abusceen ONLINE assays and GC-MS analysis. Multi-dug containing contol was made at the assay cutoff levels (benzoylecgonine, ng/ml; mophine, ng/ml; THC- COOH, 5 ng/ml; amphetamine, 1 ng/ml; and phencyclidine, 5 ng/ml), and at twice the assay cutoff levels by addition of dug stock solutions (1 mg/ml) to this uine pool. Dug concentations in these multianalyte standad (Y~S) contols (cutoff and x cutoff) detemined to be within 1% of thei tagets by GC-MS (EISohly Laboatoies, Oxfod, MS). MAS contol-containing dugs at.sx the cutoff was pepaed by dilution of the cutoff contol with the pooled nomal human uine. Dug concentations in all MAS contols wee also detemined to be within 1% of thei taget concentations by ONLINE. Nititecontaining uine specimens wee pepaed by diect spiking of sodium nitite o potassium nitite to each of the Y~,S contols containing,.5x, lx, o x of the dug cutoff levels, espectively. The final concentations of nitites in uine contols wee as follows:.1m,.5m, o 1.M (85 mg/ml KNO~. o 69 mg/ml NaNO~.). Following the dissolution of nitite salts, all the uine specimens and contol standads wee stoed at oom tempeatue and all of the assays wee pefomed days afte nitite spiking. Conductivity of uine specimens The conductivity of uine specimens containing nitites was measued using a CDC 61T platinum conductivity cell and a CDM8 conductivity mete (adiomete) at oom tempeatue. Table I. Chaacteistics of the GC-MS Confimation Assays Limit of detection Limit of quantitatlon Uppe limit of lineaity Dug Extaction Method Deivative LOD (ng/ml) LOQ (ng/ml) ULOL (n&/ml) THCCOOH liquid-liquid Methyl 1 ~ Benzoylecgonine liquid-liquid TMS' 15 Amphetamine liquid-liquid HFB Mophine liquid-liquid TMS' 5 SO Phencyclidine liquid-liquid None 1 * TMS: timethyl silyl ++ HFB: heptafluoo butyate 75

3 GC-MS analysis Uine specimens containing an appopiate amount of intenal standad (hexadeuteo-a9-thccooh, EISohly Laboatoies, Inc., Oxfod, MS) wee hydmlyzed and extacted fo GC-MS analysis accoding to the pocedue published by ElSohly et al. (5). Fo specimens used fo the bisulfite study, 5 mg sodium bisulfite was added to the specimen following the addition of intenal standad, and the mixtue was allowed to stand fo 5 ain pio to extaction (1). GC-MS analysis was pefomed using a 1-m x.18-mm DB-1 column (.-1Jm film thickness) pogammed fom ~ (.5 min) to 5~ at ~ and held 8 min. Helium was used as caie gas at 5 cn/s, splitless injecto at 5~ with a.-min delay. The ions wee monitoed at m/z 7, 57, and 1 fo THC- COOH and at m/z 78, 6, and 19 fo the hexadeutem-thccooh. Concentations of unknown specimens wee calculated elative to a calibation cuve pepaed with 6, 15, and 5 ng/ml THCCOOH with both negative and positive contols. Analyses of benzoylecgonine, mophine, amphetamine, and phencyclidine wee pefomed accoding to the standad GC-MS opeation pocedues established in the E1Sohly Laboatoies, Inc. The chaacteistics of the confimation assays ae listed in Table I. IO i" o the detection of five abused dugs using contol standads (MAS) and uine contols containing.1m,.5m, and 1.M nitite ion. The spiking by up to 1.M of nitites did not cause a visually discenible change in the physical appeaance of uine specimens. Neithe potassium nitite no sodium nitite affected the uinay ph. All nitite-spiked uine poduced stong positive eactions in nitite tests using commecially.i..: Salt concentation Figue 1. The elationship between uine conductivity and the salt concentations in uine specimens.--o--, NaCI;--17--, NaNO; and --A--, KNO. (M) Results and Discussion Nitite-adulteated uine specimens The adulteant Klea is geneally sold by deales as two plastic vials. Each vial is filled with a solid eagent weighing about.5 g that can be added diectly to uine. Assuming the volume of uine collected to the specimen containe is in the ange of to 1 ml, the nitite concentation in the specimens (ignoing the vaiation of pecent puity of potassium nitite) would be in the ange of.5 to.6m. Because of this assumption, we fist selected to evaluate Table II. Abusceen ONLINE Values* fo Nitite-Fee and Nitite-Containing Multianalyte Standads.5M nitites 1.M nitites Nitite-fee Assay standad + K Na K + Na + Amphetamine Benzoylecgonine Mophine Phencyclidine 6 5 THCCOOH The aveage values fom duplicate esults (nglml) by ONLINE analysis using the COBAS MIRA automated analyze in a semi-quantitative mode. Multianalyte standad Table III. GC-MS Analysis Assay Concentation (ng/ml) Pecent of contol standads Contol Uine standads Nitite-containing Contol Uine standads Nitite-containing nitite-fee containing 1. M uine teated nitite-fee containing 1.M uine teated standads nitite ion with bisulfite standads nitite ion with bisulfite Amphetamine Benzoylecgonine Mophine 99 9 Phencyclidine 5.6. THCCOOH % 11% 19% 6 1% 88% 9% 95 1% 98% 99%.6 1% 95% 9% 7. 1% % 89% 76

4 available uinalysis eagent stips that wee designed to detect nitite at concentations 1-1,-fold lowe than.5m. The pesence of nitite salt also changed the conductivity of uine specimens. As shown in Figue 1, the high concentation of nitites and othe salts in the uine samples inceased the ionic stength, and the conductivity of samples changed fom 11 ms/cm in the contol uine to 85 ms/cm in uine containing 1.M KNO~. ONLINE assays The effect of nitites on the pefomance of ONLINE immunoassays was examined at thee dug levels and in dugfee uine fo each of the five dug assays. The aveage value of duplicate esults fom testing uine standads that contained five dugs at thei specific cutoff level ae shown in Table II. As compaed with the nitite-fee contols, uine standads containing.5 o 1.M nitite ion showed appoximately 5 o 5% highe = m v t--..$ "= -~ ~ (D 1.$ $ 1 Amphetamine (ng/ml) ;.S = Benzoylecgonine (ng/ml) = ".5 "= --~ 1.5._m Mophine (ng/ml) ~.s.$ 1.$ 5 $ Phencyclidine (ng/ml) =. v.5 z 1.$ - --~ (D 1.5 THCCOOH assay THCCOOH (ng/ml) [] contol multlanalyte standad (MAS) [] MAS spiked with.1m nitite 9 MAS spiked with.5m nitite [] MAS spiked with 1.M nitite Figue. Evaluation of five abused dugs by the Abusceen ONTRAK assays. The esponse of the ONTRAK assay was visually ated fo the degee of latex agglutination based on an abitay unit (a.u.) of. (no agglutination) to. (total agglutination), with O.5-unit incement. Results wee expessed as the aveage agglutination scoe fom thee independent uns fo each of the test conditions. 77

5 amount of amphetamines, espectively, in the ONLINE immunoassay. By contast, uine standad containing 1.M nitite ion showed appoximately % lowe detection of THCCOOH than that of the nitite-fee contols in the ONLINE immunoassay. The dichomatic effects of nitite on the ONLINE amphetamine and THCCOOH assays wee also obseved with standad containing lowe dug concentations. In the pesence of 1.M nitite, the aveage ONLINE value fo amphetamine was inceased fom 5 ng/ml in the contol to 67 ng/ml (1% incease). In contast, the aveage ONLINE value fo THCCOOH was deceased fom 5 ng/ml in contol to 19 ng/ml (% decease). Howeve, fo all five dugs evaluated, the diffeences between the assays' esponse using the contol standads and those containing.1 mol/l of potassium nitite wee within 1%. ONTRAK assays The effect of nitites on the pefomance of ONTRAK immunoassays is shown in Figue. The degee of latex agglutination in the ONTRAK slide was assigned an abitay eading unit (a.u.) based on a to. scale with incements of.5. Results fom each of the ONTRAK slides in this study wee individually compaed to a set of photogaphs displaying eadings coesponding to the appopiate degees of latex agglutination. A eading of showed complete inhibition (no agglutination), and a eading of.5 o 1. indicated only slight ganulations. Readings fom 1.5 to. wee designated to gadually inceasing degees of latex agglutination with. indicating the stongest agglutination. Fo the field use, any agglutination (equivalent to > 1.5 a.u. in this ating system) is consideed a negative esult. The nomal noise between multiple eplicates in this assay is +.5 fo samples showing agglutination. In this study, tiplicate ONTRAK slides wee un fo each of the conditions tested and the aveage agglutination scoe was calculated and shown in Figue. No significant diffeence in the aveage agglutination scoes was obseved between the contol standads and those containing.1,.5, o 1.M of nitite salts. TESTCUP-5 assay The effect of nitites on the pefomance of the TESTCUP-5 assay is shown in Figue. Fo unifomity of on-site esult intepetation, a signal-intensity ating system was developed. Each esult was ated visually accoding to a to. scale in a.5 incement, with. colo unit (c.u.) epesenting the stongest colo. Result eadings using the ating system poduced compaable standad cuves to those obtained fom coloimetic density measuements of the test stip esult bands using a Minolta CR-1 Choma Mete (6). Standad cuves fo each assay have been geneated and photogaphed to seve as efeences fo the designated ating system. The TESTCUP assays have been calibated so that atings of (no colo) o.5 (vey faint colo) indicate positive esults, and atings of 1. (a light blue band) and above denote negative esults. As shown in Figue, the oveall accuacy of the TESTCUP-5 assay to distinguish a positive fom a negative esult was not affected by the pesence of nitite ion. Howeve, the signal intensity of the negative esult fo THC and phencyclidine assays was slightly suppessed by the pesence of high levels of nitites. GC--MS analysis Table Ill summaizes the GC-MS analysis of the contol standads, the uine MAS spiked with 1.M nitite, and nitite-spiked uine specimens that wee teated with sodium bisulfite as descibed in the Mateials and Methods section. Fo the five assays analyzed, the most significant intefeence was only obseved with the THCCOOH analysis. Thee was no detectable THCCOOH o its intenal standad in the nitite-containing uine. Howeve, the bisulfite-teatment step alleviated this poblem and esulted in 89% ecovey of THCCOOH. The spiking of nitite ion inceased the ecovey of amphetamine. It is inteesting because the pesence of nitite significantly inceased the immuno-eactive esponse fo amphetamine (Table II). Futhe studies ae waanted to povide possible explanations fo this obsevation. Sample stoage In this study, the nitites wee left in contact with the dags o dug metabolites fo days befoe the assays wee pefomed to simulate the time lag between specimen collection and laboatoy analysis. It should be noted that the duation between initial sample collection and the GC-MS confimation test may be longe than a few days, and theefoe, the stability of THCCOOH following stoage of uine in the pesence of nitite may influence the dug-test esults. In addition, the possible degadation of THCCOOH metabolite by the nitite adulteant ove time can be poblematic fo the analysis of bottle B in egulated testings. In a peliminay study, uine standads (ph 7) that had been spiked with 1.M nitite and efigeated fo weeks showed substantial ecovey of THCCOOH following bisulfite teatment (7. ng/ml afte days of stoage vesus. ng/ml afte weeks of stoage). Howeve, subsequent study demonstated that the degadation of THCCOOH in the pesence of Klea was ph dependent. Afte a -week exposue to.15m nitite in efigeated stoage, the THCCOOH was not ecoveable (% ecovey) even with bisulfite teatment if the uine standad was adjusted to ph 5 o ph 6. By contast, >9% of THCCOOH could be ecoveed following bisulfite teatment if the uine standad was adjusted to ph 8. The time and concentation limits alleviated by the bisulfite could be diffeent fom sample to sample because of the vaiation between samples in ph, ionic stength, and stoage conditions. Howeve, at the time of analysis in this study, a sufficient quantity of the bisulfite was used to decompose all nitite ions in the Table IV. GC-MS Analysis of THCCOOH Concentation of nitite ion in uine.9 mm (5 pg KNO/mL).588 mm (5 IJg KNO/mL).91 mm (1 pg KNO/mE) 5.88 mm (5 pg KNO/mL) mm (1 mg KNO/mL) Pecent of contol THCCOOH value' 96.9% 95.% 98.9% 96.% 97.8% * Pecent of contol = 1% x (ng/ml THCCOOH in nitite-containing uine)/(ng/ml THCCOOH in contol standad) 78

6 sample to ecove any undegaded THCCOOH. Nevetheless, the net ecovey of THCCOOH would vay fom sample to sample depending on uine popety and stoage time and conditions. Futhe studies ae cuently being conducted to investigate the stability of THCCOOH in the pesence of nitite in vaious uine matices and in diffeent tempeatue conditions. Moeove, patient specimens (athe than spiked specimens) contain pedominantly the acid glucuonide in combination with the THCCH. The effect of nitites on the acid glu- cuonide unde diffeent conditions will also be the subject of a futue epot. Nitite fom natual souces Although nitite is not a constituent of nomal uine, nitites can be pesent in uines fom individuals suffeing fom uinay tact infections with nitate-educing micooganisms o in specimens fom patients on medications that may metabolize to nitite (1,). It has been epoted that thee is a substantial ~-..5 D. 1.$ Amphetamine assay ( Cocaine assay e $ Amphetamine (ng/ml) O) 1.5 1$ $ Benzoylecgonine (ng/ml) 6 ~".S c~ t- 1.5._~.5 Mophine assay 15 5 Mophine (ng/ml) ~.$ v c~ t- 1.5 ~- 1 O'J.5 -~ 6 PCP assay 1.$ 5 7.S Phencyclidine (ng/ml) SO ~..S C~ 1.$ THCCOOH assay._~.5 5 $ 7$ I THCCOOH (ng/ml). Evaluation of 5 abused dugs by the ONTRAK TESTCUP-5 assay. The esponse of the TESTCUP-5 assay was visually ated fo the degee of colo fomation (colo units: c.u.) fom. (no colo) to. (stongest colo) with.s-unit incement. Results wee expessed as the Aveage Signal Colo Rating (c.u.) fom two independent uns fo each of the test conditions. -- X --, MAS uine contol; -- O --, MAS spiked with.1m nitite; -- A --, MAS spiked with.5m ni~'ite; -- []--, MAS spiked with 1.M nitite. The dotted line indicates the uppe limit of a positive esult intepetation. 79

7 diffeence between nitite concentations fom natual souces and adulteation; howeve, it is impotant to ensue that the nitite levels in non-adulteated samples ae not sufficient to poduce false-negative esults fo the THCCOOH confimation testing. Additional expeiments wee pefomed using a uine standad that contained THCCOOH at its cutoff level to detemine the effect of low concentations of nitite on the GC-MS analysis of THCCOOH. Although the pesence of mm o moe of nitite ion consideably educed the ecovey of THCCOOH and its intenal standad, a negligible diffeence in the THC- COOH ecovey was obseved when the THCCOOH single-analyte standad was spiked with a seies of nitite concentation anging fom. to 1aM (Table IV). The compehensive study by Uy et al. (1) indicated that the highest nitite concentation in uine fom natual souces in thei study was 19 pg/ml (.8aM nitite ion). They futhe estimated that the maximum nitite concentation in uine fom all souces othe than puposeful addition was mg/ml (6.5 mm nitite ion). Theefoe, uine nitite deived fom natual souces should not poduce false-negative esults fo THCCOOH confimation testing. Refeences 1. M. DeLancey and E.S. Kinkennon. Does Dug Testing Wok?The Institute fo a Dug-Fee Wokplace, Washington D.C., T. Mieczkowski and K. Lesch. Dug testing in ciminal justice. J. Natl. Inst. Justice :9-15 (1997).. G. Hemphill. Dugs of abuse testing. Adv. Med. Lab. Pofessionals Oct: 1-1 (1995).. J.M. Walsh. Dug testing, a standad business pactice. Empl. Assist. 1:6-9 (1995). 5. Ameican Management Association. Wokplace Dug Testing and Dug Abuse Policies. New Yok, NY, D.B. Fase. Labs scamble to keep pace with schemes fo defeating tests. Foensic Uine Dug Test. Aug: 1-6 (1997). 7. L.A. Boussad. Sample adulteation and othe challenges. Foensic Uine Dug Test. Dec: 1-6 (199). 8. S.D. Peason, K.O. Ash, and F.M. Uy. Mechanism of false-negative uine cannabinoid inmunoassay sceens by Visine eye dops. Clin. Chem. 5:66-68 (1989). 9. A. Wane. Intefeence of common household chemicals in immunoassay methods fo dugs of abuse. Clin. Chem. 5: (1989). 1. E. O~Conno, D. Ostheime, and A.H.B. Wu. Limitations of foensic uine dug testing in methodology and by adulteation. AACC TDM/Tox. 1:77-88 (199). 11. S. Geoge and R.A. Baithwaite. The effect of glutaaldehyde adulteation of uine specimens on Syva EMIT II dug-of-abuse assays. ]. Anal. Toxicol. : (1996). 1. M.A. EISohly, S. Fen& W.J. Kopycki, T.R Muphy, A.B. Jones, and D. Cat. A pocedue to ovecome intefeences caused by the adulteant "Klea" in the GC-MS analysis of 11-no-gg-THC-9 - COOH. J. Anal ToxicoL 1:- (1997). 1. F.M. Uy, G. Komaomy-Hille, B. Staley, D.K. Cockett, M. Kushni, G. Nelson, and R.E. Stuemple. Nitite adulteation of wokplace uine dug testing specimens I. 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