Exemplos de análises ambientais - EPA
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Analytical Capabilities
General Chemistry Analyses
The Lab performs a full range of classical water quality analyses including:
Alkalinity
Ammonia
Anions
BOD
Cyanide
Hardness
Nitrate/Nitrite-N
Sulfide
Total Dissolved Solids (TDS)
Total Suspended Solids (TSS)
Total Kjeldahl Nitrogen (TKN)
Total Organic Carbon
Perchlorate
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In addition, the following determinations for soil are performed:
Total organic carbon
Grain Size
Moisture in soil
pH in soil
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Exemplos de análises ambientais – EPA (continuação)
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Metals
Metals in water, soil and animal tissue are determined by a variety of techniques at the Region 9
Laboratory.
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Inductively Coupled Plasma Spectrometry (ICP) - The Region 9 Lab operates
an ICP coupled with an atomic emission spectrometer and an ICP coupled with
a mass spectrometer. After applying one of several digestion techniques to a sample, the digested
sample is introduced into the ICP which is capable of measuring up to 24 inorganic elements
simultaneously. Concentrations are usually in the parts per billion (ppb) to parts per million (ppm)
range.
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Graphite Furnace Atomic Absorbance (GFAA) - After applying one of several digestion
techniques to a sample, the digested sample is introduced into the GFAA system which measures
a single element at a time. Concentrations are usually in the sub ppb range.
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Cold Vapor Atomic Absorbance Mercury Analyzer (CVAA) - Is used for determine mercury
concentration. Currently a quanitation limit down to 30 ppt is possible.
Typical metals analyses available from the Region 9 Laboratory are:
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Antimony, Arsenic, Barium, Beryllium, Boron, Cadmium, Calcium, Chromium, Copper, Cobalt,
Iron, Lead, Magnesium, Manganese, Mercury, Molybdenum, Nickel, Potassium, Selenium, Silver,
Sodium, Strontium, Thallium, Tin, Vandium, Zinc
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Exemplos de análises ambientais – EPA (continuação)
Volatile Organic Chemicals/Pesticides
Gas Chromatography - The Region 9 Laboratory uses several gas chromatographs equipped with
different selective detectors to measure a variety of organic chemical constituents in environmental
samples. These include:
Petroleum hydrocarbons in water and soil with a GC equipped with a flame ionization detector (FID)
Chlorinated Pesticides and Polychlorinated Biphenyls (PCBs) in water, soil/sediment and animal
tissue with a GC equipped with an electron capture detector (ECD).
1,2-Dibromoethane (EDB) and 1,2-Dibromo-3-Chloropropane (DBCP) in water by GC-ECD.
Gas Chromatography/Mass Spectrometry - A gas chromatograph (GC) coupled with a mass
spectrometer (MS) is used to separate, identify and quantitate volatile organic compounds in water and
soil and semivolatile organic compounds in water, soil and animal tissue. The fuel oxygenate, Methyl
Tert-Butyl Ether (MTBE) is a recent addition to the target analyte list of volatile organic compounds,
bringing the total number of compounds on the list to 42. The target analyte list of semi-volatile organic
compounds includes over 60 compounds including phenol, naphthalene, and benzo(a)pyrene.
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Exemplos de análises ambientais – EPA (continuação)
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Pesticide Screening by Immunoassay - Using an immunochemical analytical
technique (ELISA), the Region 9 Lab can analyze samples for individual pesticides.
This method can be applied to either solid or liquid media and offers fast turnaround
time and low cost relative to traditional pesticide methods. ELISA (short for EnzymeLinked ImmunoSorbent Assay) is not suitable for compliance monitoring purposes,
although it can provide determinative data for preliminary sample screening in a
larger study.
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Air Toxics
Using a cryofocusing preconcentrator and a GC/MS, the Region 9 Laboratory
analyzes for 39 volatile organic compounds in air down to the 1 ppb level. The
procedures used are consistent with EPA Methods TO-14 and TO-15.
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Other Analyses
Bulk Asbestos by Polarized Light Microscopy (PLM)
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Alkalinity
• Measure of acid-neutralizing capacity (ANC)
• Analysis by titration with mineral acid (HCl or H2SO4) –
determination using pH indicators or potentiometers
• Chemical species involved (CO3)-2, (HCO3)- & OH• Oily matter, ppcts. may interfere but cannot be removed since
they contribute to ANC
• For low alkalinity samples (<20), the equivalence point must be
determined by extrapolation
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Hardness
• Defined as the sum of [Ca] e [Mg] and expressed as CaCO3
• Total hardness = Temporary hardness (alkalinity) + Permanent
hardness
• Determination by complexometric titration with EDTA
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Conductivity
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Measures the ability of an aqueous solution to carry an electrical current
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Reflects the degree of mineralization of a water: the higher the amount of
dissolved salts the higher the conductivity
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Measured by conductivimeters and expressed in micro-Siemens/cm
C=
K
R
where: C= conductivity in mS/cm or μS/cm, K= cell constant and R=electric resistance
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Solids
• Total Solids (TS): residue left after heating the sample at a defined
temperature (103ºC, 175ºC/185ºC or 525ºC)
• The difference between the total solids determined at 175ºC/185ºC
and the same parameter determined at 575ºC corresponds to the
organic matter content of the sample.
• Total Suspended Solids (TSS): portion of the solids retained by a
filter.
• Total Dissolved Solids (TDS): portion of the solids that passes
through a filter.
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DISSOLVED OXYGEN (DO)
• Electrometric (Electrode)
– More common
– Rate of diffusion of molecular O2 across membrane
• Winkler Method
– Add Mn+2 + strong base, DO oxidizes Mn+2 to higher ordered
Mn(OH)x+2. Add I-/H+; Mn goes back to Mn+2 and equivalent I- is
liberated. Titrate with (S2O3)-2 w/starch indicator. (S2O3)-2 must be
standardized at least quarterly.
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ANIONS BY ION CHROMATOGRAPHY
• HPLC w/conductivity detection (300.0, 4110)
• Multi-element capability @ μg/l sensitivity
• Anions: F-, Cl-, Br-, (NO2)-, (NO3)-, (SO4)-2, (PO4)-3 and
others
• F- often difficult to quantify; can be done
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ION
CHROMATOGRAPHY
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HALOGEN IONS (F-, Cl-, Br-, I-)
• Analytical Options
– Colorimetric
– Titrimetric
– IC
– Ion-Selective Electrodes (ISE)
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ION SELECTIVE ELECTRODES
• Measure the activity of free ions in solution
• Interferences known & controllable
• Must control T & ionic strength
• Can measure halides, S-2, NH3 and (CN)-
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CYANIDE (CN-)
• All CN groups that can be determined as CN• Total Cyanide measures all free & bound CN• Measurement Options
– Titration
– Colorimetry
– ISE
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NITROGEN SPECIES
• Forms of N to be measured:
– (NO3)– (NO2)– NH3
– Organic N
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AMMONIA (NH3 )
• Measurement Options
– Titration
– ISE
– Phenate w/ or w/o automation
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AMMONIA (NH3 )
• Titration
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Only used after distillation
H3BO3 added to decrease hydrolysis of organo-N species
Titrate w/std. H2SO4; end-pt. either w/indicator or electrometrically
Useful below 5 mg/L
• ISE
– Gas-permeable membrane to measure NH3(aq) & (NH4)+ converted to NH3(aq)
by pH adjust. to 10-11
• Phenate
– Indophenol (VERY blue) is made from reaction between NH3, (ClO3)- &
phenol catalyzed by nitroprusside
– Measure spectrophotometrically @ 640 nm
– Interfering Ca & Mg can be complexed
– Can be easily automated
– RSD’s much better than titrimetry or ISE
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(NO2)- and (NO3)-
• Both can be done by IC
• (NO2)- can also be done by spectrophotometry
• (NO3)– UV-Spec.
– ISE
– Cd Reduction
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ORGANIC (KJELDAHL) N
• Measures N as NH3
• Kjeldahl N is the same as organic N.
• Digest sample, convert to NH3, and measure as per NH3 options.
• Does not measure e.g., azide, azo, nitro, nitroso, nitrite or nitrate N
species
• Macro: low [NH3], requires larger sample volume (500 ml.)
Micro: higher [NH3]
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PHOSPHOROUS SPECIES
• P analyses consist of 2 steps
– Digestion converts phosphorous to orthophosphate
– Colorimetric determination
• Reactive P (Orthophosphate): respond to colorimetry w/o
hydrolysis or oxidation
• Organic P: Fraction convertible to orthophosphate by destruction
of organic matter
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SULFITE (SO3)-2
• Occurs in boilers, feedwaters and treatment plant effluents
• Method Options
– Iodometric: KI titration with starch indicator
– Colorimetric: (easier) Reaction with 1,10-phenanthroline and vis.
detection at 510 nm.
SULFATE (SO4)-2
– IC (BEST CHOICE)
– Turbidimetry: BaSO4 ppct. light scattering is measured (MOST
COMMON)
– Gravimetry: (Ppct. as BaSO4)
– Titrimetry: xs. Ba is complexed w/methylthymol blue to yield blue color
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SULFIDE (S-2)
• “Total S-2” includes both H2S & HS- as well as acid-soluble metallic
sulfides; [S-2] very low
• There are several qualitative tests
• Quantitative Methods: I- oxidizes S-2 / H+
– Titration: OK if [S-2] > 1 ppm
– Iodimetric
– ISE
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Biochemical Oxygen Demand
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Measures molecular O2 used during the biochemical degradation of organic
matter (C) in water
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Usually applied to determine waste loadings to treatment plants & efficiency of
control measures
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5 day test: BOD5
20 day test: BOD20
60-90 day test: UBOD
Fill sample to overflow & seal airtight
Incubate for fixed time
Measure DO initially & @ end
BOD = Final[DO] - Initial[DO]
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TOTAL ORGANIC CARBON (TOC)
• Better expression of organic content than BOD
• TOC is independent of the ox. state of the organic matter
and does not measure H or N
• Organic molecules ⇒ C ⇒ CO2
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Metals
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Analytical Tecniques:
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Inductively Coupled Plasma Spectrometry (ICP) –
ICP coupled with an atomic emission spectrometer: ICP-AES
ICP coupled with a mass spectrometer: ICP-MS
ICP is capable of measuring up to 24 inorganic elements simultaneously.
Concentrations are usually in the parts per billion (ppb) to parts per million
(ppm) range.
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Graphite Furnace Atomic Absorbance (GFAA) - After applying one of
several digestion techniques to a sample, the digested sample is introduced
into the GFAA system which measures a single element at a time.
Concentrations are usually in the sub ppb range.
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Cold Vapor Atomic Absorbance Mercury Analyzer (CVAA) - Is used for
determine mercury concentration. Currently a quanitation limit down to 30
ppt is possible.
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ICP - Inductively Coupled Plasma
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ICP, abbreviation for Inductively Coupled Plasma, is one method of optical
emission spectrometry.
When plasma energy is given to an analysis sample from outside, the
component elements (atoms) are excited. When the excited atoms return to low
energy position, emission rays (spectrum rays) are released and the emission
rays that correspond to the photon wavelength are measured.
The element type is determined based on the position of the photon rays, and
the content of each element is determined based on the rays' intensity.
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To generate plasma, first, argon gas is supplied to torch coil, and high frequency
electric current is applied to the work coil at the tip of the torch tube. Using the
electromagnetic field created in the torch tube by the high frequency current,
argon gas is ionized and plasma is generated.
This plasma has high electron density and temperature (10000K) and this
energy is used in the excitation-emission of the sample. Solution samples are
introduced into the plasma in an atomized state through the narrow tube in the
center of the torch tube.
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Typical metal analysis in environmental samples
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Calcium
Chromium
Copper
Cobalt
Iron
Lead
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Potassium
Selenium
Silver
Sodium
Strontium
Thallium
Tin
Vandium
Zinc
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Etapas da análise cromatográfica
1. Extracção dos analitos a partir da matriz na qual se encontram
2. Purificação e concentração dos compostos a quantificar
3. Introdução da amostra no sistema cromatográfico
4. Separação cromatográfica
5. Detecção: Os detectores cromatográficos produzem sinais
eléctricos que são enviados para registadores ou integradores
Cada detector produz uma resposta (sinal eléctrico) cuja
intensidade é proporcional à concentração do analito.
Esta resposta do detector depende também da natureza do analito o
que torna obrigatória a utilização de padrões dos compostos a
quantificar.
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Picos cromatográficos
Linha de base: resposta do detector quando nenhum analito está a ser
detectado
Deverá ser estável ao longo da corrida cromatográfica e corresponder a
um sinal eléctrico baixo e sem flutuações (razão sinal/ruído grande)
Para que se possam quantificar os picos cromatográficos deverão estar
razoávelmente resolvidos: deve ser possível localizar o início e o fim de
cada pico bem como o seu máximo.
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Determinar a concentração
• Normalização interna
• Utilização de factores de resposta
• Calibração externa
• Calibração com padrão interno
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Normalização interna
•Calcular a área total de todos os picos da amostra (excepto o de
solvente) e assumir que:
•Cada componente produz um pico
•A resposta do detector não depende da natureza da substância
•Nestas condições admite-se que a concentração de um
componente 1, C1 é dada por:
C1 (%) = (Area 1 / Area total ) x 100
•É apenas um valor indicativo pois não tem em consideração a
influência da natureza dos vários compostos detectados na
resposta do detector
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Calibração Externa
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A calibração deve ser efectuada com uma mistura de padrões que inclui
todos os analitos a ser quantificados numa gama de concentrações
idêntica à das amostras reais
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As condições de análise devem ser reproductíveis: estado do
equipamento, condições de introdução da amostra, volume de amostra,
etc.
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Nestas condições:
– Avalia-se a gama na qual a relação entre a resposta do detector e a
concentração do componente é linear.
– Determina-se a resposta da mistura de padrões a quantificar em pelo menos
5 níveis de concentração uniformemente distribuídos pela gama de
linearidade
– Calcula-se a equação de correlacção entre área e concentração
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Método do padrão interno
•Um composto que não faz parte da amostra (padrão interno) é adicionado,
numa concentração conhecida, antes de se efectuar à análise.
•Procede-se como no caso da calibração externa mas:
• Utiliza-se a razão A1 / Api em vez de A1
onde A1 é a area do pico correspondente ao componente 1 e Api é a area do
pico correspondente ao padrão interno
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Utiliza-se a razão C1 / Cpi em vez de C1
onde C1 é a concentração do componente 1 e Api é a concentração do
padrão interno
Desta forma eliminam-se fontes de erro associadas ao processo de injecção: variação
do volume de injecção, actividade no injector ou no topo da coluna, etc
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Unidade de Biotecnologia Ambiental, FCT/UNL
Características de um bom padrão interno
• Não pode existir na matriz a partir da qual se extraem as amostras
reais
• Padrões deuterados
• Deve ser estável nas condições da análise
• Não pode co-eluir com outros componentes da amostra (analitos ou
impurezas).
• Não pode afectar o padrão de eluição dos outros componentes da
amostra
• Tem que ser adicionado numa concentração constante a todas as
amostras e todos os padrões de calibração
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Representação esquemática de um cromatógrafo gasoso
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Specific detectors
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HPLC system with multidetection
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Unidade de Biotecnologia Ambiental, FCT/UNL
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Air Toxics
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Type of Compounds Determined
Sample Collection Device
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Volatile organic compounds
Volatile organic compounds
Volatile organic compounds
Pesticides/PCBs
Aldehydes/Ketones
Phosgene
Anilines
Phenols
Dioxins
Tenax® solid sorbent
Molecular sieve sorbent
Cryotrap
Polyurethane foam
Impinger
Impinger
Adsorbent
Impinger
Polyurethane foam
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Pesticides/PCBs
Aldehydes/ketones
Non-methane org. comp. (NMOC)
Polycyclic aromatic hydrocarbons
Volatile organic comp. (nonpolar)
Volatile org. comp. (polar/nonpolar)
Volatile organic compounds
Volatile organic compounds
Polyurethane foam
Adsorbent
Canister or on-line
Polyurethane foam
Specially-treated canister
Specially-treated canister
Open path monitoring
Single/multi-bed adsorbent
Analytical Methodology
GC/MS
GC/MS
GC/FID
GC/MD
HPLC
HPLC
GC/MS
HPLC
HRGC/HRMS
GC/MD
HPLC
FID
GC/MS
GC/MS and GC/MD
GC/MS
FTIR
GC/MS, FID, etc.
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