Analytical Forensic Toxicology Exam 2

GC, Sample Prep

gc

internal standard addition

always after dilution to ensure same amount in each sample

how to choose a method

AMR chosen and capability of instrument

AMR

analytical measured range

AMR

range you can quantitate and report a value based on method validation

internal standard purpose

verification, identification, quantitation

istd verification

extraction succesful

itsd comparison

identify compound through retention time comparison 

istd quantitation

calibration curve

verify before report

calibration % dev, controls in range, negative blanks, no carryover, ion ratios, itsd recover, retention time, rrt, chromatography

istd for non specific detector

similar structure, not found in sample, no shared common ion, same extraction, acceptable chromatogram 

istd for mass spec

isotopically labeled version if analyte or matched

matched isotope 

adding deuterium

istd accounts for 

any loss in sample

standard addition

generate quant results within sample instead of performing external

standard addition common use

difficult matrix like liver tissues

low pka=

stronger acid=donates proton more

pH variable dependent on 

matrix and/or extraction solvent

__ ideal

2 pH units away from pKa

amphoteric compounds

has both acidic and basic groups, act as either

zwitterion

has both a pos and neg charge at the same time

direct analysis sample prep types

enzyme immunoassay, headspace

dilute and shoot pros

simple, cheap, easy

dilute and shoot cons

potential loss of recovery by diluting analyte

protein precipitation

dilution and take out matrix components by denaturing proteins

types of extraction 

LLE, SPE, SLE, PLD

LLE

liquid liquid extraction

SPE

solid phase extraction

SLE

supported liquid extraction

PLD

phospholipid depletion

derivatization limitation

can make the molecule too large to volatize 

derivatization requirements

heat, time, catalyst, removal of reactant 

derivatization goal

chemically react with problematic molecule in native form and convert to gc acceptable form 

derivatization outcomes

improve chromatogram, differentiate optical isomers, create charge for LCMS

gc main contaminants

oxygen, moisture, hydrocarbon 

Mass spec instrument components

sample introduction, transfer region, high vacuum, pumps, ionization source, analyzer, detector, data processor

GCMS diagram

electron ionization

disrupt electron cloud to cause loss of an electron and create a radical catio

base peak

ion with the greatest relative abundance

molecular ion

parent compound minus one electron

acylation functional group

silylation functional groups