Comparison of Ethanol and Other Drugs of Abuse Concentrations in ...

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Journal of Analytical Toxicology, Vol. 34, September 2010

Technical Note

Comparison of Ethanol and Other Drugs of Abuse Concentrations in Whole Blood Stored in Venoject® Glass and Plastic and Venosafe™ Plastic Evacuated Tubes Ritva Karinen1,*, Elisabeth Leere Øiestad1, Wenche Andresen1, Grete Wethe1, Anne Smith-Kielland2, and Asbjørg Christophersen1 1Division

of Forensic Toxicology and Drug Abuse, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, 0403 Oslo, Norway and 2The Department for Quality, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, 0403 Oslo, Norway

Abstract The aim of this study was to evaluate the stability of blood concentrations of a variety of illegal and medicinal drugs that are important for forensic analyses when spiked and stored in Vacutainer® or Venosafe evacuated plastic collection tubes compared to Vacutainer evacuated glass tubes. Tubes were filled with spiked whole blood and analyzed after storage for one week at ambient temperature and at –20°C, respectively. Freeze-andthaw stability was included in the study. No significant difference between storage in glass or plastic tubes was noted for any compound investigated.

duction of the Vacutainer evacuated glass tubes was signalled (personal communication). It was important to find tubes with identical or similar anticoagulant additives and enzymatic inhibitors and without conventional closures, as the tubes have to be opened and closed several times. In addition, it would be convenient with tubes with similar dimensions in order to fit our sampling kits. Before replacing the glass tubes by plastic tubes, the stability of ethanol and other drugs of abuse collected in the different tubes had to be examined.

Methods Introduction Knowledge of the influence on drug stability and possibility of adsorption to or interference from collection tubes is of great importance in analytical toxicology. Differences in stability and adsorption have been demonstrated for several substances, including ethanol, in plasma and serum (1–10). One study that included whole blood discussed the impact of storage conditions and collection tubes on ethanol concentrations (10), but to the best of our knowledge, no studies of the influence of blood collecting devices on the concentration of other drugs in whole blood have been published. The aim of this study was to evaluate plastic tubes as a replacement for glass tubes. We have used 5-mL BD Vacutainer evacuated glass tubes with BD Hemogard™ Closure containing the preservatives sodium fluoride and heparin, for collection of whole blood samples for forensic purpose, such as drivers suspected of driving under the influence of drugs. Plastic tubes could, however, be a better alternative due to fewer problems with breakage. In addition, a possible discontinuation in pro* Author to whom correspondence should be addressed. Email: [email protected].

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Two types of evacuated tubes, 5-mL glass BD Vacutainer (product number ref # 367764, additives sodium fluoride (NaF)/heparin) and 4-mL plastic BD Vacutainer (product number ref # 368921, additives NaF/ potassium oxalate), were purchased from BD Diagnostics (BD, Plymouth, U.K. and Franklin Lakes, NJ, respectively), and 4-mL plastic Venosafe (product number VF-054SFH, additives NaF/sodium heparin) were obtained from Terumo (Terumo Europe N.V., Leuven, Belgium). The human whole blood was supplied by the Blood Bank of Oslo at Ullevaal University Hospital in Oslo, Norway. Reference substances were obtained from commercial suppliers. Aliquots of blood were spiked at two concentration levels with alcohols and a selection of drugs of abuse and other psychoactive medicinal drugs commonly found in forensic cases in Norway (Tables I–V). Blank blood and spiked blood were then filled in the different tubes by using Venoject Multisample needles (Terumo Europe N.V.). One-half of the tubes was stored at ambient temperature for one week. They were rotated for one-half hour on each of the four first days to simulate the conditions during transport of sample tubes to the laboratory. The other half was stored in a freezer at –20°C for approxi-

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Table I. Alcohols: Deviation (%) from Target Value after One-Week Storage Target (mg/ Compound 100 mL)

Ambient Temperature A*

B

C

A

B

C

Ethanol

447.7

– –5.9 0.4

– –5.9 1.4

– –6.2 0.8

– –2.8 0.1

– –3.1 0.0

– –3.6 –0.2

15.6 153.8

4.3 2.1

4.8 3.1

5.4 2.4

4.3 1.5

4.8 1.2

6.0 1.2

Methanol

25.5

Freezer (–20°C)

Target (mg/ Compound 100 mL)

Ambient Temperature A

B

C

A

B

C

Isopropanol

26.7 200.1

0.0 1.3

0.7 2.3

0.6 1.8

0.3 –0.4

–0.1 –0.6

–0.2 –0.9

Acetone

28.6 219.0

–0.2 2.0

–0.2 3.3

–1.0 2.1

1.1 0.3

–0.4 –2.1

–2.1 –2.9

Freezer (–20°C)

* A = Vacutainer glass tube; B = Vacutainer plastic tube; and C = Venosafe plastic tube.

Table II. Benzodiazepines and Related Drugs: Deviation (%) from Target Value after One-Week Storage* Target Compound (mg/L)

Ambient Temperature

Freezer (–20°C)

A†

B

C

A

B

C

Compound

Target (mg/L)


B

Freezer (–20°C)

C

A

B

C

–11.3 –11.2

–7.3 –11.8

–8.3 –6.8

–8.9 –9.7 –9.7 –11.0

Clonazepam

0.01 0.4

4.1 –0.5

1.5 –3.0

2.2 –1.5

–5.2 10.2

8.9 2.6

–1.7 2.5

Fenazepam

0.006 –9.1 0.02 –12.5

Nitrazepam

0.02 –9.0 0.07 –12.4

–9.9 –14.3

–12.0 –16.2

–11.7 1.8

4.1 –2.4

–2.2 –1.8

Nordiazepam

0.08 0.3

10.3 –2.7

7.4 –4.5

4.6 –4.2

3.8 –0.9

3.3 –1.8

–0.8 –1.0

Flunitrazepam 0.002 0.3 0.007 –2.2

–4.9 –5.8

–9.0 –4.8

6.7 –10.6

9.2 –9.5 –16.3 –15.8

Diazepam

0.08 0.3

14.9 1.1

14.7 –0.3

10.3 –0.6

15.0 7.7

1.4 11.7

–0.9 9.3

–4.2 –17.6

–3.0 –22.3

–0.9 –5.9

–1.2 –11.8

1.6 –8.1

Zopiclone

0.05 –72.1 0.2 –90.4

–71.5 –91.0

–66.9 –90.5

24.0 –10.0

6.9 2.4 –10.8 –12.5

Zolpidem

0.03 –14.6 0.08 –17.4

–14.1 –17.9

–12.7 –15.7

–10.0 –4.1

Lorazepam

0.02 –5.3 0.06 –20.2

Oxazepam

0.4 1.5

13.0 –7.2

12.5 –3.4

14.4 –5.3

3.8 –6.3

Alprazolam

0.02 0.05

3.3 –2.0

1.0 –2.2

–2.0 –4.5

1.2 5.8

6.2 4.4

21.3 12.8 –11.4 –12.8 –9.3 –4.9

–8.3 –6.4

–0.2 1.8

* Sample preparation: liquid–liquid extraction on ChemElute® columns. † A = Vacutainer glass tube; B = Vacutainer plastic tube; and C = Venosafe plastic tube.

Table III. Opiates and Opiods: Deviation (%) from Target Value after One-Week Storage Target Compound (mg/L)

Ambient Temperature

Freezer (–20°C)

A*

B

C

A

B

C

Compound Methadone†

Target (mg/L)


B

C

–0.6 0.3

–5.3 –4.6

Freezer (–20°C) A

B

C

–4.3 –4.8

0.1 3.6

–2.6 4.9

–1.2 4.2

5.3 7.5

4.5 13.2

Morphine†

0.01 0.04

4.1 1.5

4.3 1.0

2.2 1.4

9.7 7.5

9.1 5.6

8.2 7.0

Codeine†

0.02 –7.9 0.05 –10.1

–6.7 –13.0

–6.5 –4.2

3.2 –5.2

2.2 –2.1

1.0 –1.3

Ketobemidone‡ 0.02 –14.7 0.1 –31.2

–22.4 –39.6

–15.3 –32.7

12.3 14.4

–8.7 –25.4

–8.5 –18.3

–10.2 –27.4

11.9 –11.3

10.0 –5.0

21.0 5.2

Tramadol‡

–23.7 –40.5

–17.0 –33.5

–16.3 –23.5

–19.5 –14.3 –7.7 –15.5

Oxycodone†

0.03 –12.9 0.08 –22.6

–15.9 –24.0

–9.4 –16.4

3.6 –2.7

1.9 –3.2

2.0 –1.8

Propoxyphene‡ 0.1 0.5

–11.5 –29.0

–2.2 –22.1

–12.2 –20.2

–9.7 –16.4

Fentanyl†

0.002 –0.8 0.005 2.9

2.2 –2.6

–3.6 –8.7

3.8 1.2

12.8 5.0

–1.7 2.6

Ethylmorphine† 0.1 0.3

0.1 0.3

0.08 –16.6 0.4 –31.9 –8.0 –22.5

–6.0 –9.3

* A = Vacutainer glass tube; B = Vacutainer plastic tube; and C = Venosafe plastic tube. † Sample preparation: liquid–liquid extraction on ChemElute columns. ‡ Sample preparation: protein precipitation.

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mately one week. They were subsequently thawed and frozen three times before analysis to mimic the procedures of possible reanalysis of samples stored in a freezer. The samples were analyzed before dispensing and after storage in tubes at ambient temperature and in freezer. The techniques used were headspace gas chromatography with

flame-ionization detection (FID) for alcohols and acetone (11) and gas chromatography with FID for GHB. Sample preparation for GHB was liquid–liquid extraction with dichloromethane/hexane after conversion to GBL with sulfuric acid, followed by neutralization with potassium hydroxide. For the remaining compounds, ultra-performance liquid chromatog-

Table IV. Psychostimulants: Deviation (%) from Target Value after One-Week Storage* Target Compound (mg/L)

Ambient temperature A†

B

Freezer (–20°C)

C

A

B

C

Compound

Ambient temperature

Target (mg/L)

A

B

Freezer (–20°C)

C

A

B

C

0.07 –10.1 0.2 –14.9

–8.3 –14.5

–9.0 –14.4

–3.3 –13.9

–0.8 –2.5 –14.5 –11.5

Cocaine

0.1 0.3

–53.5 –60.1

–53.6 –60.5

–54.3 –61.3

–10.9 –11.4

–10.9 –10.6 –9.7 –12.0

Metamphetamine 0.09 –26.3

Methylphenidat

0.02 –64.3 0.06 –66.5

–69.7 –69.0

–68.1 –70.3

–13.9 –9.5

–16.8 –24.2 –22.4 –19.7

Amphetamine

MDMA

0.2

–21.2

–22.7 –20.8

–27.9 –20.4

–19.0 –12.6

–19.5 5.0

–9.5 1.7

0.1 0.4

–3.1 –11.5

–6.9 –13.0

–7.2 –17.7

1.6 –19.3

0.4 4.1 –17.0 –16.3

* Sample preparation: liquid–liquid extraction on ChemElute® columns. † A = Vacutainer glass tube; B = Vacutainer plastic tube; and C = Venosafe plastic tube.

Table V. Miscellaneous Drugs: Deviation (%) from Target Value after One-Week Storage Target Compound (mg/L) THC† GHB Ketamine‡

A*

B

C

–15.1 12.1

–9.6 15.5

–4.5 17.9

–6.0 27.7

–5.7 31.8

Venlafaxine‡

0.09 –11.9 0.5 –28.3

6.6 3.5

8.5 4.0

9.0 4.4

1.8 2.5

4.1 3.2

5.5 3.3

Citalopram‡

0.07 –8.3 0.3 –24.8

0.07 –12.8 0.4 –28.2

–16.3 –36.4

–11.3 –28.7

–16.6 –24.5

–16.0 –15.8 –29.7 –23.8

Pregabalin‡

1.1 5.3

–6.2 0.9

–4.4 4.7

–14.1 –7.4

15.5 23.9

Gabapentin‡

2.6 13.1

0.03 –20.9 0.1 –24.2

–32.3 –36.3

–30.2 –32.6

–9.7 –7.3

12 68

22.3 45.2

26.7 46.9

–19.3 –15.7 –11.8 –8.2

Compound

Ambient Temperature

Target (mg/L)

A

0.002 –17.8 0.008 11.3

B

Freezer (–20°C)

C

Levome0.08 promazine‡ 0.4 Mirtazapine‡

Ambient Temperature

Atomoxetine‡

A

B

Freezer (–20°C)

C

A

B

C

–19.5 –36.3

–11.6 –27.6

–15.8 –21.7

–18.1 –34.8

–12.2 –28.4

–1.3 –7.8

–8.3 –18.6

–4.6 –4.7

13.3 5.6

14.6 4.2

3.1 2.3

6.0 0.7

7.3 0.9

7.4 1.2

6.4 1.8

6.8 2.7

6.2 5.9

–5.7 –16.5

0.06 –11.9 0.2 –0.3

–13.4 –1.6

–11.2 –3.2

2.5 19.7

–19.6 –17.9 –27.6 –23.0

–5.7 –5.8 –16.9 –19.9 2.3 16.4

–0.1 16.8

* A = Vacutainer glass tube; B = Vacutainer plastic tube; and C = Venosafe plastic tube. † Sample preparation: liquid–liquid extraction on ChemElute columns. ‡ Sample preparation: protein precipitation.

Table VI. Alcohols: Deviation (%) Between Two Tubes after Storage at Ambient Temperature Concentration (mg/100 mL)

Vacutainer Glass – Vacutainer Glass

Vacutainer Plastic – Vacutainer Plastic

Venosafe Plastic – Venosafe Plastic

Vacutainer Glass – Vacutainer Plastic

Vacutainer Glass – Venosafe Plastic

Ethanol

25.5 447.7

0.4 –0.7

0.5 0.2

–0.2 –1.0

–0.1 –1.4

0.7 –0.3

Methanol

15.6 153.8

1.9 –1.2

1.4 0.4

–1.8 –1.4

–0.2 –1.8

0.8 –0.2

Isopropanol

26.7 200.1

0.9 –0.3

0.4 0.0

–0.6 –0.1

–0.4 –1.2

0.3 –0.6

Acetone

28.6 219.0

1.3 –0.9

0.1 0.4

–0.6 0.1

0.6 –1.9

1.8 –0.6

Compound

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raphy–tandem mass spectrometry (UPLC–MS–MS) (12), high-performance liquid chromatography–mass spectrometry (LC–MS) or tandem mass spectrometry (LC–MS–MS) were used. Samples analyzed by UPLC–MS–MS (Tables II–V) were prepared by supported liquid–liquid extraction on ChemElute® columns with ethylacetate/heptane. Sample preparation for compounds analyzed by LC–MS or LC–MS– MS was protein precipitation (acetonitrile or acetonitrile/ methanol, Tables II–V). The blank samples were also

screened by an immunological method (EMIT®) for a standard selection of drugs of abuse (amphetamines, cannabis, cocaine, and opioids). Two sample tubes were used for each drug class, and three aliquots from each sample tube were analyzed. The same calibration standards were used in all analyses to avoid random errors by differences in preparation of the standards. Each of the analysis series of the stored blood samples consisted of 54 spiked samples in addition to blank samples, stan-

Table VII. Alcohols: Deviation (%) Between Two Tubes after Storage in Freezer (–20°C) Concentration (mg/100 mL)






Ethanol

25.5 447.7

0.1 0.5

–0.2 –0.4

0.0 0.5

0.4 0.5

0.9 0.2

Methanol

15.6 153.8

–0.4 0.8

–0.8 –0.7

–1.1 0.9

–0.3 1.0

–1.2 0.2

Isopropanol

26.7 200.1

0.3 0.6

–0.2 –0.2

0.5 0.1

0.6 0.6

0.4 0.7

Acetone

28.6 219.0

0.9 2.2

–1.8 –1.0

0.6 0.1

2.7 3.9

3.2 4.2

Compound

Table VIII. Benzodiazepines and Related Drugs: Deviation (%) Between Two Tubes after Storage at Ambient Temperature Compound

Concentration (mg/L)






Clonazepam

0.01 0.4

6.4 2.1

6.5 7.0

9.5 6.6

2.4 0.0

0.2 –1.3

Nitrazepam

0.02 0.07

7.1 8.1

7.9 11.4

9.3 9.3

0.6 0.4

2.3 3.7

Flunitrazepam

0.002 0.007

10.6 –1.4

5.1 9.3

5.0 0.6

7.9 –1.7

11.8 1.8

Lorazepam

0.02 0.06

–3.5 –0.6

2.9 5.8

0.7 5.6

–4.4 –6.7

–4.6 –0.5

Oxazepam

0.4 1.5

–2.7 0.0

–0.4 4.0

–1.8 0.1

–0.6 –6.2

–1.7 –2.1

Alprazolam

0.02 0.05

1.2 2.3

6.7 4.9

8.1 10.1

–0.6 –1.2

1.6 –1.6

Fenazepam

0.006 0.02

0.8 1.2

7.4 5.0

3.8 –1.8

–0.9 –3.4

–3.5 0.7

Nordiazepam

0.08 0.3

–0.4 2.1

1.7 4.8

1.0 4.1

1.6 0.5

4.5 0.5

Diazepam

0.08 0.3

4.7 –0.1

0.7 2.6

6.4 6.9

2.2 –0.1

3.2 –1.9

Zopiclone

0.05 0.2

–6.5 –14.6

–20.3 –56.1

–36.1 –38.6

4.4 –0.7

–3.4 –6.0

Zolpidem

0.03 0.08

4.1 –3.1

–3.1 1.1

–0.8 1.9

3.0 –1.5

0.2 –4.6

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Table IX. Benzodiazepines and Related Drugs: Deviation (%) Between Two Tubes after Storage in Freezer (–20°C) Compound







Clonazepam

0.01 0.4

4.8 –0.2

0.3 14.3

16.1 11.2

–2.8 –0.3

–0.8 1.4

Nitrazepam

0.02 0.07

7.6 1.0

2.0 10.8

3.9 1.9

–0.2 –0.8

4.9 3.1

Flunitrazepam

0.002 0.007

–8.7 –0.7

5.2 19.2

10.4 20.7

–17.0 –3.9

–8.7 –5.4

Lorazepam

0.02 0.06

–0.3 1.3

1.1 4.8

1.2 2.1

–0.4 4.6

–3.4 2.0

Oxazepam

0.4 1.5

4.9 1.8

1.4 9.6

4.9 11.8

–1.2 1.0

1.3 1.6

Alprazolam

0.02 0.05

1.2 –1.6

2.8 10.7

11.8 8.1

–5.8 –5.1

–4.1 –1.1

Fenazepam

0.006 0.02

0.6 –5.0

1.1 3.3

0.4 4.7

0.4 –1.0

1.7 –0.3

Nordiazepam

0.08 0.3

1.5 –5.5

0.9 3.2

0.3 2.6

–3.0 –3.4

–1.8 –4.0

Diazepam

0.08 0.3

–1.5 2.3

–0.9 0.3

5.7 8.0

–1.7 –2.8

–4.2 –4.5

Zopiclone

0.05 0.2

–8.4 –3.4

–6.1 19.6

23.4 27.5

1.0 –11.1

–4.6 –14.4

Zolpidem

0.03 0.08

5.7 2.8

0.6 –7.8

–9.9 1.4

1.9 5.9

5.7 3.0

Table X. Opiates and Opioids: Deviation (%) Between Two Tubes after Storage at Ambient Temperature Compound







Morphine

0.01 0.04

3.4 1.2

0.8 1.2

1.3 4.2

1.1 0.5

2.8 –1.4

Codeine

0.02 0.05

0.8 0.8

2.4 8.0

0.8 –10.3

–2.1 –0.4

–1.6 –0.9

Ethylmorphine

0.1 0.3

8.7 3.0

9.8 –19.4

10.5 2.1

–0.8 1.6

0.7 3.2

Oxycodone

0.03 0.08

–8.3 1.1

–1.7 8.8

2.6 –10.6

0.3 –2.1

–9.7 –1.9

Fentanyl

0.002 0.005

–0.4 0.5

2.7 10.2

11.5 11.5

–4.7 0.6

–3.4 6.2

Methadone

0.1 0.3

–0.5 8.0

–2.2 2.0

3.4 2.7

5.6 7.8

1.8 7.6

Ketobemidone

0.02 0.1

–4.7 9.9

–3.6 –2.7

12.7 –2.1

8.5 17.6

–8.4 7.9

Tramadol

0.08 0.4

–11.2 11.8

–7.8 0.1

9.6 3.4

7.1 17.7

–10.4 6.5

Propoxyphene

0.1 0.5

–13.5 3.3

–22.3 –3.8

–4.2 –4.3

7.6 11.6

–11.1 3.2

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dards, and controls. These samples were analyzed in two batches in order to detect possible variation within series.

Results and Discussion The results for the various drugs, presented as mean deviation (%) after storage either at ambient temperature or in freezer and compared to time zero (target value), are given in Tables I–V. The deviation (%) between the two tubes of the same type together with the deviation (%) between Vacutainer glass tube and the plastic tubes are given in Tables VI–

XV. The calculated deviations are based on the average of three replicates for each tube. The statistical analysis has been performed by simple comparison of the deviation from the target value. Only two sample tubes were used for each level in order to minimize the amount of human blood for the experiment. The mean deviation of the blood ethanol concentration tested after storage at ambient temperature or in freezer (Table I) showed a difference between all the three blood collection tubes of only 1%. Differences were within ±1.0% between the same types of tubes and ±1.4% between Vacutainer glass tubes and plastic tubes (Tables VI–VII). Similar results were found in a previous study (10) where no systematic differences for

Table XI. Opiates and Opioids: Deviation (%) Between Two Tubes after Storage in Freezer (–20°C) Compound







Morphine

0.01 0.04

–1.9 2.2

1.8 –3.3

2.2 –1.3

–1.4 4.4

–0.7 2.2

Codeine

0.02 0.05

–6.5 –11.4

–3.0 –4.7

–11.2 –0.3

–0.7 –6.8

4.3 –9.9

Ethylmorphine

0.1 0.3

–3.2 –2.2

–9.4 –9.0

–17.9 –21.6

4.6 –3.6

–0.9 –8.2

Oxycodone

0.03 0.08

0.9 –3.6

–7.3 –6.0

–4.3 1.1

5.6 1.7

4.0 –3.3

Fentanyl

0.002 0.005

–16.5 –8.7

1.8 0.8

7.4 –4.8

–18.7 –8.7

–6.5 –3.4

Methadone

0.1 0.3

5.0 2.4

5.3 –5.8

–3.9 –7.1

2.6 2.8

5.6 4.1

Ketobemidone

0.02 0.1

–13.6 –10.8

–11.8 18.9

–9.8 –7.2

8.1 17.6

–8.5 –7.7

Tramadol

0.08 0.4

2.9 5.6

–10.9 –23.7

–12.1 –8.9

10.2 20.1

4.9 13.4

Propoxyphene

0.1 0.5

–16.9 –15.2

–14.8 12.3

–15.5 –5.9

–3.9 –2.1

–7.8 –9.6

Table XII. Psychostimulants: Deviation (%) Between Two Tubes after Storage at Ambient Temperature Compound







Amphetamine

0.07 0.2

4.1 2.8

2.1 3.9

–1.5 2.8

–1.0 –1.0

1.6 –0.5

Metamphetamine

0.09 0.2

12.0 4.6

–2.1 4.2

–7.3 0.6

2.5 –0.3

11.3 1.0

MDMA

0.1 0.4

0.9 8.0

3.2 9.3

0.0 –5.7

2.8 1.0

4.7 13.2

Cocaine

0.1 0.3

6.4 0.0

–2.6 6.7

4.2 1.4

4.7 –2.6

2.8 2.4

Methylphenidate

0.02 0.06

13.5 14.5

4.7 8.7

–12.7 8.3

19.0 10.2

21.6 14.3

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ethanol concentrations were found for whole blood collected with two different collection tubes. The differences in the mean deviations for the other alcohols were within ± 2.0% and for acetone within ± 3.0% in all the three blood collection tubes tested after storage at ambient temperature or in freezer (Table I). The differences between the same types of tubes for methanol, isopropanol, and acetone concentrations varied from –1.8 to 2.2%, and the differences between plastic tubes compared to Vacutainer glass tube were between –1.9 and 4.2% (Tables VI–VII).

The mean differences in deviations (%) of the blood concentrations for the other drugs were within 18% in all the three types of tubes tested after storage at ambient temperature or in freezer (Tables II–V). The deviations between the same type of blood collection tubes after storage at ambient temperature (Tables VI, VIII, X, XII, and XIV) were within ± 30% for all compounds tested, except for zopiclone, which is known to be an unstable compound (13). The deviations between Vacutainer glass tubes versus plastic tubes were within ± 22% for all drugs.

Table XIII. Psychostimulants: Deviation (%) Between Two Tubes after Storage in Freezer (–20°C) Compound







Amphetamine

0.07 0.2

–2.7 –0.2

2.6 5.0

10.5 1.5

–5.4 –2.0

–7.8 –3.6

Metamphetamine

0.09 0.2

9.9 12.7

2.0 –13.9

–9.6 –5.2

4.6 –5.2

–1.3 –6.2

MDMA

0.1 0.4

7.0 3.5

0.3 –3.0

–9.9 –6.6

4.5 0.5

5.9 1.4

Cocaine

0.1 0.3

–0.3 –3.4

–0.8 –3.2

–4.1 –2.8

0.3 –2.0

1.5 0.4

Methylphenidate

0.02 0.06

–1.3 1.8

–7.2 12.3

3.2 –3.6

6.2 9.5

9.9 13.6

Table XIV. Miscellaneous Drugs: Deviation (%) Between Two Tubes after Storage at Ambient Temperature Compound THC GHB

Concentration (mg/L) 0.002 0.008 12 68






–15.0 –8.1

–1.4 –5.4

–9.8 –11.2

–10.2 –2.0

–12.6 –2.1

–0.3 1.7

0.6 0.7

0.2 0.4

–2.3 0.0

–2.5 –0.2

Ketamine

0.07 0.4

–12.0 11.2

–10.9 1.7

7.6 0.9

3.5 15.7

–12.1 5.8

Levomepromazine

0.08 0.4

17.0 6.5

21.6 16.9

4.0 10.9

–4.5 –9.7

14.5 6.0

Mirtazapine

0.03 0.1

–2.9 12.4

–4.5 0.7

16.3 7.7

15.0 20.9

0.8 13.3

Venlafaxine

0.09 0.5

–16.9 9.1

–10.7 –2.7

11.0 2.7

5.9 16.3

–15.1 2.3

Citalopram

0.07 0.3

–5.7 9.9

–1.8 4.0

11.6 8.4

9.0 15.9

–4.6 5.4

Pregabalin

1.1 5.3

23.8 11.2

14.3 3.6

–0.4 –12.4

4.0 5.1

20.0 13.9

Gabapentin

2.6 13.1

5.5 –0.3

3.6 –3.3

–6.9 –6.2

0.6 0.6

6.2 –1.0

–4.1 –4.0

–1.7 –0.1

–1.1 1.9

0.5 –0.5

–2.4 0.0

Atomoxetine

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0.06 0.2


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Table XV. Miscellaneous Drugs: Deviation (%) Between Two Tubes after Storage in Freezer (–20°C) Compound


THC GHB

0.002 0.008 12 68



6.7 1.3

2.5 –7.9

1.5 –0.2




–18.9 –12.9

3.7 –3.5

12.8 –4.4

–3.1 0.9

–1.3 0.4

0.1 –1.3

–2.2 –1.1

Ketamine

0.07 0.4

–9.4 1.6

–10.8 –15.9

–10.4 –10.9

–0.1 14.5

–0.5 12.6

Levomepromazine

0.08 0.4

–8.8 –17.1

–5.8 –14.5

–4.3 –16.4

–7.4 –18.7

–3.8 –20.8

Mirtazapine

0.03 0.1

–12.9 –4.7

0.6 –16.2

6.9 –16.6

4.6 9.9

–2.9 13.8

Venlafaxine

0.09 0.5

–10.8 –6.2

–6.6 –20.0

–12.1 –11.9

2.6 13.4

3.0 12.2

Citalopram

0.07 0.3

–7.6 –9.1

–10.0 –21.6

–10.4 –12.1

8.1 16.7

4.6 7.2

Pregabalin

1.1 5.3

14.3 2.5

3.5 8.3

1.1 0.0

4.3 –3.2

5.4 0.8

Gabapentin

2.6 13.1

10.4 9.5

6.3 5.8

4.5 –1.2

2.1 2.4

3.1 9.2

–3.8 3.2

1.2 3.8

2.4 5.0

–2.4 2.5

–0.5 1.5

Atomoxetine

0.06 0.2

After storage in freezer (Tables VII, IX, XI, XIII, and XV) the deviations between sample tubes of the same type were also within ± 30% for all the compounds tested. The deviations between glass and plastic tubes were within ±21% for all compounds.

Unni Johansen, Ida Nord, Linda Ambjørnrud, Dhaya Srikumar, Ingvild Vandås, Sidsel Holm, Saba Tekie, Kirsten M. Olsen, and Bente R. Larsen for performing the analyses and Jørg Mørland for valuable comments and for critical reading of the manuscript.

Conclusions

References

There were no significant differences in the drug concentrations of blood samples stored in glass tubes and in plastic tubes. The blank samples did not show any interfering peaks or false-positive results with the analytical or immunological methods used for any of the compounds after storage at the same conditions as the spiked samples. A deviation in concentration between replicates of up to 30% is considered acceptable for our forensic samples, except for ethanol analysis. The measured deviations in glass and plastic tubes were within this range, and the use of plastic tubes either in addition to or as replacement for the previously used glass tubes therefore appears to be acceptable.

Acknowledgments We want to thank Inger Hasvold, Gerd-Wenche Brochman,

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Manuscript received February 11, 2010; revision received March 29, 2010.