Forensics - Chap11

analytical chemistry definition

analytical chemistry definition

the science of obtaining, processing, the communication information about the composition and structure of matter

analytical chemistry provides...

answers to equations such as what is the element or molecular composition of sample and how much of each component is present

analytical chemistry focuses on

- separation
- purification
- characterization
- identification
- quantification of the components that make up a sample

classics (wet chemical)

based upon well known chemical reactions of the compounds being studied

classical pos

- retain an important place in forensic investigation
- very accurate
- quickly adaptable
- less expensive
- less sensitive to impurities

classical uses

includes a variety of field tests (very convenient to use away from lab as a quick indication of the nature of a substance)

physical (property and instrumental)

deals with using specially designed and often complex to measure and analyze the physical properties of a sample

physical pos

- most common laboratory analyses in forensic investigations
- requires for less sample
- very reproducible
- can be run very rapidly on many sample

presumptive test

provide a rapid screening process to determine the likelihood of a particular chemical presence in a sample

presumptive test pos

used to determine whether additional, more conclusive testing is warranted

presumptive test negative

can give fal/pos or false readings

presumptive test examples

spot test

spot test

very quick and simple presumptive test to indicate the presence of a particular element or substance

marquis test

changes color based of which substance is present (drug testing)

confirmatory test

a measurement that can indicate the presence of the substance in the sample with a very high degree of certainty

confirmatory test pos

reduces false readings

gravimetric analysis

focuses on mass measurement from chemical reactions to determine quantitatively how much of something is present in a sample

combustion analysis

- type of gravimetric analysis
1. a pure organic compound is completely blasted with an excess of oxygen in to ensure that the original sample is completely consumed
2. converts all the organic chemical to CO2 and water

volumetric (titration) analysis

involves determining the amount of an analyte found in a solution by reacting it completely to with a known amount of another solution

equivalence point

the point of which all of the analyte is exactly consumed in the reaction

titration

a process where a measure volume of a solution with an unknown concentration is added to a known volume of another solution just until the reaction between them is exactly complete

exact point of neutralization

the marking along its length of the burette tube allow the determination of the volume of reactant used to reach the equivalence point

immunoassay

techniques based on immunoassay to determine the concentration of biologically important material
ex. toxins, body fluids)

indicator

compound used that changes color at the endpoint

analyte

the target substances for which for analysis is being done

concentration

the amount of material dissolve in a given amount of solvent

quantitative

determination of how much of a component is present

qualitative

determining the identity of a particular substance (quality of material)

isotopes

atoms that vary in the number of neutrons while keeping the same number of protons

isomers

stranding same set of atoms together in different ways produce new substances

conservation of mass

the total amount of material present before and after a chemical reaction is the same

physical properties

measured w/o changing the compound chemically into something else

chemical properties

changing the molecules into something chemically different through chemical reaction

intrinsic properties

don't rely on how much sample is involved

extrensic properties

depend on same size
- mass
- volume
- heat

molarity equation

M = mol/vol

chromatography

a technique that separates a mixture into its components by passing it over a stationary phase while being carried by a mobile phase

stationary phase

common substance

mobile phase

the carrier containing the mixture components

chromatography steps

1. mixture to be separated is added to the beginning of the stationary phase
2. the mobile phase than carries the components across the stationary phase, causing the separation to occur

gas chromatography (GC)

used gas to push the components apart (separates using strength of interaction)

affinity

the strength of this attraction

retention factor

the distances a component moved down the column it paper strip divided by the distance movies by the pure solvent (solvent front)

retention time (GC)

the amount of time that it takes a compound to emerge from end of the column

mol equation

mol = g/(g/mol)

analytical methods

- quantitative or qualitative
- sample size and sample preparation
- what level of analysis is required
- detection levels and useful analytical concentration ranges
- destructive or nondestructive
- availability of instrumentation
- admissibility