Analyses of water

1
Analyses of water Expt.1 Pesticides in water
2
Classification of pesticides According to 1.
Target organism insecticides, fungicides,
herbicide.. 2. Chemical properties OC, OP,
carbamate.. 3. Mode of actionstomach poison,
contact poison..
3
1940-1970s synthetic OCs (e.g.DDT) widely
used. Persistent, conc. in lipid tissues (along
food chains). Major environmental hazards (DDT
t1/2 1-10 y). OPs shorter half-lives (few d,
malathion). carbamates OPs highly toxic to man
same effect per kg/body weight, unlike OCs.
4
Structures of common pesticides, (A) chlorinated
hydrocarbons, OCs (B) organophosphorus compounds,
OPs (C) carbamates.
5
Mode of action of OPs Acetylcholine (AC)
involved in nerve impulse transmission from one
cell to another. Must be cleared after each
impulse, by enzyme acetylcholinesterase (ACHE),
which hydrolyses it. OPs and carbamates
interfere with synaptic transmission by
inhibiting ACHE, so AC cannot be
hydrolysed. Carbamate poisoning more easily
treated removal of carbamate permits (slow)
enzyme regeneration
6
(No Transcript)
7

• Specification of chlorpyriphos technical
• http//www.parijatagrochemicals.com/Chlorpyriphos.
  htm
• 1999 Risk assessment
• http//www.safer-world.org/d/chem/chlorpyr.htm
• Chemet products
• http//www.chemetchemicals.com/alfagin_chemethion_
  action.htm
• WHO Assessment
• http//www.inchem.org/documents/jmpr/jmpmono/v074p
  r11.htm
• MSDS
• http//www.parijatagrochemicals.com/cmsds.htm

8
Gas chromatography Convert sample to vapour,
which distributes between stationary phase
(nonvolatile liquid supported in column)
carrier gas eluent. Components in complex
mixtures separate because they partition
differently between gas liquid phases. Result
chromatogram, plots detector response time.
(Relative) retention time is used for qualitative
analysis. Peak area for quantitative analysis.
9
(No Transcript)
10
Properties and Characteristics of Typical
Gas-Chromatographic Columns
11

• Open tubular columns
• WCOT - glass capillary tubes coated with thin
  layer of SP.
• SCOT - column efficiency gt for small particles,
  but gas p needed is proportional to 1/d2.
• Both superceded by FSOT - high purity silica (low
  in metal oxides). Flexible, with thin walls
  coated by polyimide on outside and SP on inside.

12
(No Transcript)
13
(No Transcript)
14

• Requirements for stationary phase
• 1. non-volatile 2. thermally-stable 3.
  chemically inert 4. selective-gives quick
  separation of analyte.
• Polarity of stationary phase should match that of
  analytes.
• Then elution order largely determined by B Pts.

15
collector electrode 200V current ? no. reduced
carbon atoms/unit time
Insensitive to H2O rugged, sensitive
16
npd 10-13 g/s of N or P
Ideal gc detector stable (to
400C), reproducible, fast, sensitive, linear
response, nondestructive, similarity in
response/selectivity in response.
TED
Electrolytic conductivity
Linear dynamic ranges of gas chromatographic
detectors TED, thermionic emission PID,
photoionization FID, flame ionization ECD,
electron capture TCD, thermal conductivity and
FPD, flame photometric.
PID
FID
ECD (dc)
ECD (pulsed)
TCD
FPD
0.001
1
1000
Linear range, ng
17
Rubidium silicate bead (-180 V) at 1.25 cm above
flame tip, electrically heated to 600-800 oC.
Inside bead vaporn - ionizn - recapture by bead
of Rb and e- flow to collector. Enhanced by N,P
compds which form FR in flame. (CN ? CN- P ?
PO2- Rb ? Rb. Low-T flame, suppresses normal
fid response of C cpds.
N, P sensitive detector
18
Flame photometric detector, fpd

• Selective for S, P.
• Eluent passes into low-T H2/air flame which
  converts P partly to HPO, which has emission
  bands 510-526 nm. Also S ? S2, emits at 394 nm.
  Suitable filters isolate these bands, and their
  intensities are measured photometrically.

19
Website Link for gas chromatographyhttp//fat
e.clu-in.org/gc.asp?techtypeid44
20
GC-MSD ms produces, separates and detects ions
in gas phase
interface
21
Processes in msd 1. M ? Mn ne- by
electron-impact source. 2. separate ions
according to mass/charge ratio, by fixing Vdc/Vrf

in quadrupole
mass analyzer, then ?
each one m/e reaches the detector at a time
22
Electron multiplier detector
23
ms detector enables identification of molecular
species from mass spectrum. TIC mode complete
mass spectrum is scanned for each peak. SIM mode
complete mass spectra not taken during analysis,
but ms detector is tuned to only certain
pre-selected masses. More sensitive than TIC mode.
24
TIC and ms of cocaine in urine