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Forensic Drug Testing Part 2: GC/MS Confirmation. Roger L. Bertholf, Ph.D. Associate Professor of Pathology Chief of Clinical Chemistry & Toxicology. Low cost Fast Semi-quantitative High sensitivity Low specificity. High cost Slow Quantitative High sensitivity High specificity.

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forensic drug testing part 2 gc ms confirmation

Forensic Drug TestingPart 2: GC/MS Confirmation

Roger L. Bertholf, Ph.D.

Associate Professor of Pathology

Chief of Clinical Chemistry & Toxicology

screening vs confirmation
Low cost

Fast

Semi-quantitative

High sensitivity

Low specificity

High cost

Slow

Quantitative

High sensitivity

High specificity

Screening vs. Confirmation
a confirmatory method should
A confirmatory method should . . .
  • Utilize the most accurate (specific) testing method available
  • Have sensitivity equal to or better than the screening method
  • Be economically feasible
  • Be simple enough to standardize across many laboratories
  • Produce results that are legally defensible
chromatography
Chromatography
  • Separation of components based on their. . .
    • Solubility in mobile and stationary phases
  • Terminology:
    • Gas/liquid
    • Liquid/liquid
    • Ion exchange
    • Partition
chromatographic separations
Chromatographic separations

Mobile Phase

Stationary Phase

chromatographic separations6
Chromatographic separations

A

B

Soluble in stationary phase

Long retention time

Soluble in mobile phase

Short retention time

chromatographic separations7

A

B

Chromatographic separations

The resolution of a chromatographic

separation is defined as:

t/mean peak width

Detector signal

Time

chromatographic resolution9
Chromatographic resolution
  • The resolution, Rs, is a unitless quantity since it is the ratio of two measures of retention (time, volume, or distance).
  • In general, in order to satisfactorily separate equal amounts of compounds A and B, the Rs must be greater than 0.8—baseline separation requires an Rs greater than 1.25.
the van deemter equation
The van Deemter equation
  • = Flow rate

A = Eddy diffusion component

B = Longitudinal diffusion component

C = Mass transfer term

the van deemter equation15
The van Deemter equation
  • = Flow rate

A = Eddy diffusion component

B = Longitudinal diffusion component

C = Mass transfer term

gc injection techniques
GC injection techniques
  • Split injections
  • Splitless (Gröb) injections
  • On-column injections
split injections
Split injections

Septum

Purge/carrier gas inlet

Injector

body

Split valve

Purge gas exit (90 – 99%)

To GC column (1 – 10%)

splitless injections
Splitless injections

Septum

Purge/carrier gas inlet

Injector

body

Split valve (shut)

Purge gas exit

To GC column (>95%)

other inlet systems
Other inlet systems
  • Solid probe
  • Liquid chromatograph
  • Mass spectrometer?
electron impact ionization

Focusing

lens

From GC

+

+

To MS

+

Ion volume

(or source)

(-)

Electron impact ionization

Power supply

Filament

e-

e-

Collector

(+)

other ionization methods
Other ionization methods
  • Chemical ionization
  • Thermospray
  • Electrospray
  • Fast atom bombardment (FAB)
  • Matrix-assisted Laser Desorption (MALDI)
other types of mass filters
Other types of mass filters
  • Ion trap
  • Ion cyclotron
  • Time of flight
electron multiplier

From mass filter

e-

104 e-

+

Ammeter

Electron multiplier

Negative dynode

Positive dynode

cocaine
Cocaine

C17H21NO4

MW=303.35

slide31

82 (base peak)

182 [M-121]+

303 (M+)

121

[M-31]+ 272

slide33

82 (base peak)

182 [M-121]+

303 (M+)

121

[M-31]+ 272

slide35

44

91

slide37

44

91

slide39

58

91

thc cooh detection

THC-COOH glucuronide (15%)

Hydrolysis

THC-COOH

BSTFA

TMS-THC-COOH

THC-COOH detection
slide59

Thank You!

Questions?