Chemicalanalysisin the biorefinery–inorganics 4.5.2010, 8...

transcript

416509.0 The Forest based Biorefinery: Chemical and

Engineering Challenges and Opportunities (5 cr)

3-7.5.2010

Chemical analysis in the biorefinery – inorganics

4.5.2010, 8:30–10:45

Johan Bobacka

Laboratory of Analytical ChemistryBiskopsgatan 8, FI-20500 Åbo-Turku

Finland

e-mail: johan.bobacka@abo.fi

Objective• Instrumental methods that are widely used for analysis of

inorganic components will be presented and discussed

• The main focus will be on basic principles and uniquefeatures of the following methods:

– Atomic absorption spectroscopy (AAS)

– Atomic emission spectroscopy (AES, ICP-OES)

– Inductively couple plasma-mass spectrometry (ICP-MS)

– Ion chromatography (IC)

– Ion-selective electrodes (ISEs)

Reference: D.C. Harris, Quantitative Chemical Analysis, 7th edition, Freeman, USA, 2007.

The Analytical Process

• Formulating the question → Selecting analytical procedures →Sampling → Sample preparation → Analysis → Reporting and interpretation → Drawing conclusions

• Classical methods (gravimetry, titrimetry)– Accurate

• Instrumental methods (electrochemistry, spectroscopy, chromatography, …)– Fast

– Sensitive

Spectroscopy

• Spectrophotometry is any technique that uses light to measurechemical concentrations

• Light waves consist of perpendicular, oscillating electric and magnetic fields (electromagnetic radiation)

• Plane-polarized electromagnetic radiation of wavelength λ:

• Ordinary, unpolarized light has electric field components in all planes

Spectroscopy

• Electromagnetic radiation can be described in terms of bothwaves and particles

• Each wave has a certain wavelength, λ, and frequency, ν

νλ = c = speed of light (2.998×108 m/s in vacuum)

• Each particle (photon) carries a certain energy, E

E = hν (h = Planck’s constant = 6.626×108-34 Js)

Electromagnetic spectrum

High frequencymeans

High energy !

Low frequencymeans

Low energy !

What happens when a molecule absorbs light?

• Absorption of light increases the energy of a molecule

• Emission of light decreases the energy of a molecule

Excited singlet and triplet electronic states

• When a molecule absorbs a photon, the molecule is promoted to a more energetic excited state

• Excited state in which the spins are opposed is called a singlet state. If the spins are parallel we have a triplet state.

• In general vibrational and rotational transitions occur as well

Absorption of light

A substance/molecule absorbs light of the same

energy, which is required to excite the molecule to a

higher energy level

A substance absorbs light of CERTAIN SPECIFIC

WAVELENGTHS. The other wavelengths are not

absorbed !

Spectrophotometric analysis

• The absorbance of light is measured when a specificwavelength of light passes through the sample

• Monochromatic light = light with a specificwavelength

Irradiance, P

• P0 The irradiance of incoming light

• P The irradiance of outgoing light

• Irradiance, P, is the energy per second per unitarea of the light beam [W/m2]

• Irradiance, P, is also called intensity, I

P ≤ P0

Transmittance, T

• Transmittance is the fraction of the original light that passes through the sample

• T has the range 0 to 1

• Percent transmittance is 100×T and rangesbetween 0 and 100 %

= =P I

DIMENSIONLESS

Absorbance, A

0 0log log logP I

A TP I

= = = −

DIMENSIONLESS

I/I0 T A

1 1 (100%) 0

0.1 0.1 (10%) 1

0.01 0.01 (1%) 2

Beer-Lambert law

• Absorbance is directly proportional to concentration

– ε molar absorptivity [M-1cm-1]

– b length of the light path through sample [cm]

– C concentration [mol/l]

DIMENSIONLESSA b Cε= ⋅ ⋅

Molar absorptivity, ε

• Depends on wavelength, λ

b, C constantλ λ( )A f ε=

Example: The UV-vis spectrum of the (ferrozine)3Fe(II) complex as a functionof wavelength, λ (b and C are constant)

Atomic spectroscopy

• In atomic spectroscopy, samples are vaporized and decomposed into atoms in a flame, furnace, or plasma at very high temperature (2000–8000 K).

• Elements in the vaporized sample absorb or emit lightat certain specific wavelengts

• Absorbed or emitted light is used to determine the concentration of the elements in the sample.

An important difference betweenatomic and molecular spectroscopy

• Absorption and emission bands of gaseous atomsare very narrow (~0.001 nm) in comparison to solidand liquid samples (~100 nm).

• Usually little overlap between spectra of differentelements in the sample

• Some instruments can measure more than 70 elements simultaneously

Atomic spectroscopy

• Principal tool of analytical chemistry

• High sensitivity

• Complex samples can be analysed

• Low concentrations can be measured– from ppm (µg/g) to ppt (pg/g) levels

• Multielement analysis possible

• Automated methods of analysis

Atomic spectroscopy

• Atomic spectroscopy divided into:

– Atomic absorption spectroscopy (AAS)

– Atomic emission spectroscopy (AES)

– Atomic fluorescence spectroscopy (AFS)

Atomic spectroscopy

Atomic absorption spectroscopy (AAS)

2000–3000 KLight path

Emits light of the λ that is absorbed by the analyte

log logP

= − = −

Atomic emission spectroscopy

Atomic emission spectroscopy (AES)

• Collisions in the very hot plasma promote someatoms to excited electronic states from which theycan emit photons to return to lower energy states. Emission intensity is proportional to concentration.

• No lamp is needed

• Today AES is the dominant form of atomicspectroscopy

Atomization of the sample

• Decomposes the sample into atoms, whichcan be analyzed with different techniques

• Different methods of atomization:– Flame

– Electrically heated furnace

– Plasma

Flame atomization

• Premix burner

– Fuel, oxidant and

sample are mixed beforegoing into the flame

– The sample is transportedto the nebulizer through a thin capillary

Flame atomization

• Nebulizer– Creates an aerosol

from the liquidsample

Flame atomization

• Glass bead– Splits the aerosol to even

smaller particles

• Baffles– Mix the aerosol

– Drops of the same sizepasses to the flame (largerdrops are trapped by the baffles)

– ∼5% of the aerosol reachesthe flame

Flame atomization

• Drop size distribution– The drop size distribution should be even in order to

obtain a stable signal with small relative standarddeviation

Flame atomization

• Combinations of fuel and oxidant– A mixture of acetylene and air is commonly used

Flame atomization

• The flame– Aerosol (sample) entering the preheating region is

heated in the primary reaction cone (blue cone)

– Combustion is completed in the outer cone

Furnaces

• An electrically heatedgraphite furnace– More sensitive than a

flame (the atomizedsample stays longer in the optical path in the furnace)

– Requires less sample(1 – 100 µl)

– Maximum recommendedtemperature: 2550 oC

Electrically heated graphite furnace

• L´vov platform– Gives more uniform

heating of the sample

– Solid samples can be analysed withoutsample preparation

Inductively coupled plasma (ICP)

• The temperature is twice as hot as a combustionflame

• T = 6000–10000 K

• Plasma: partially ionized electrically conductinggas (the fourth aggregation state)

• The high temperature, stability and relatively inertAr environment in the plasma eliminate much of the interference encountered with flames.

• Two induction coils (27 MHz or 41 MHz) around the quarz tube

• High-purity Ar is used as plasma gas

• A spark generated by the Tesla coilresults in ionization of the argon gas

• Free electrons are accelerated by the radio-frequency field and collidewith atoms:

⇒ transfers energy to the Ar gas⇒ keeps the temp. at 6000-10000 K

• Argon coolant gas protects the torchfrom overheating.

The Boltzmann distribution

• The degree of atomization of the sample is determined bythe temperature and shows how much of the sample is in the ground and excited state.

N*: number of atoms in the excited stateN0: number of atoms in the ground stateg*: number of excited statesg0: number of ground statesT: temperature (K)k: Boltzmann’s constant (1.381×10-23 J/K)

−∆= ⋅0

Inductively coupled plasma opticalemission spectroscopy (ICP-OES)

• Also called: inductively coupled plasma atomicemission spectroscopy (ICP-AES)

• ICP-OES allows multielement analysis and giveslower detection limits than flame-AAS.

• Sensitivity is improved further by detecting ions witha mass spectrometer (ICP-MS)

Inductively coupled plasma–massspectrometry (ICP-MS)

• Solid samples can be analysed by using laser ablation (LA-ICP-MS)

Detection limits of atomic spectroscopy(ng/g = ppb ”parts per billion”)

Chromatography

• Chromatography follows the same principle as extraction, but one phase is held in place (stationary phase) and the other phase moves (mobile phase) past it.

• If solute A has agreater affinity than solute B to the stationary phase, then A moves more slowly:

Two types of columns:- Packed

- Open tubular

Adsorption chromatography- separates molecules by adsorption on a solid phase

• Stationary phase

– Solid

• Mobile phase

– Liquid or gas

Partition chromatography- separates molecules by partitioning into a liquid phase

– Liquid bonded to a solid surface(SiO2)

• Mobile phase

– Gas

Ion-exchange chromatography- separates ions by electrostatic interactions

– Anions such as –SO3-

or cations, such as –N(CH3)3

+ are covalently attachedto a solid phase(resin)

• Mobile phase

– Liquid

Molecular exclusion chromatography-separates molecules by size

• Also called: gel filtration or gel permeation chromatography

– Porous gel

• Mobile phase

– Liquid or gas

Affinity chromatography- separates molecules by selective molecular interactions

– Selective moleculesare covalentlyattached(immobilized) to the stationary phase

• Mobile phase

– Liquid

The chromatogram

• Retention time: tr

• Adjusted retention time: tr´ = tr – tm

– where tm is the minimum retention time (unretained mobile phase)

• Relative retention (for components 1 and 2): α = tr´2 / tr´1

– where tr´2 > tr´1 (α >1)

The chromatogram• For each peak in the chromatogram the capacity factor, k´,

is defined as:k´ = (tr – tm)/tm = tr´ / tm

– The longer a component is retained by the column, the greater is the capacity factor

• The capacitay factor is related to the partition coefficient, K, (known from solvent extraction), where Vs is the volumeof the stationary phase and Vm is the volume of the mobile phase:

k´ = K×(Vs/Vm)

• Relative retention (for components 1 and 2) can also be expressed as:

α = tr´2 / tr´1 = k´2 / k´1 = K 2 / K 1

Efficiency of separation

• Two factors contribute to how well twocomponents are separated by chromatography:– Difference in elution times between peaks: ∆tr

– The average width of the two peaks: wav

Efficiency of separation

• Resolution = ∆tr / wav

Column efficiency

• Plate height: H = σ2 / x– where σ is the standard deviation of the Gaussian band

and x is the distance travelled

• Plate height, H, is the constant of proportionalitybetween the variance, σ2, of the band and the distance it has travelled, x.

• The smaller the plate height, the narrower the bandwidth.

High-Performance Liquid Chromatography(HPLC)

• HPLC uses high pressure to force solvent through closedcolumns containing very fine particles that give high-resolution separations.

• The column– Length: 5–30 cm

– Inner diameter: 1–5 mm

• The guard column– Replaceable

– Collects irreversiblyadsorbed impurities

• The stationary phase

• The stationary phase– Commonly microporous particles of silica

• The stationary phase– Commonly: R = octadecyl (C18)

– ODS = octadecylsilane

• In adsorption chromatography, solvent moleculescompete with solute molecules for sites on the stationary phase

• The eluent strength, εo, is a measure of the solventadsorption energy– εo for pentane is defined as 0 for adsorption on bare

silica

• Normal-phase chromatography– Polar stationary phase

– More polar solvent has higher eluent strength

• Reversed-phase chromatography– Nonpolar stationary phase

– Less polar solvent has higher eluent strength

• Isocratic elution– Elution is performed with a single solvent (or constant

solvent mixture)

• Gradient elution– Increasing amounts of solvent B are added to solvent A

to create a continuous gradient

– Used to obtain sufficiently rapid elution of allcomponents

Injection and detection in HPLC

• Injection valve

Injection and detection in HPLC

• Detector– Sensitive to low concentrations of every analyte

– Provides linear response

– Does not broaden the eluted peaks

– Insensitive to changes in temperature and solvent composition

Ion Chromatography (IC)

• Ion chromatography (IC) is a high-performanceversion of ion-exchange chromatography that is used for separation and determination of ions

• Ion chromatography (IC) has many commonfeatures with HPLC

Ion Chromatography (IC)

• Suppressed-ion anion chromatography– A mixture of anions is separated by ion-exchange and

detected by electrical conductivity

• Suppressed-ion cation chromatography– A mixture of cations is separated by ion-exchange and

detected by electrical conductivity

• Suppression = removal of unwanted electrolyteprior to conductivity measurement

Suppressed-ion anion chromatography

K+ + OH- H2O+H+

Suppressor:

Suppressed-ion cation chromatography

H+ + Cl- H2O+OH-

Suppressor:

Ion chromatography of pond water

valuesin µg/ml(ppm)

Ion-selective electrodes (ISEs)Potentiometric ion sensors

• ISEs for 60 analytes (Na+, K+, Cl-, Ca2+, H+, ….)

• ISEs respond to ion activity

• Compact, portable, low-cost instruments

• Billions of measurements / year

Reviews:

E. Bakker, P. Bühlmann, E. Pretsch, Chem. Rev. 97 (1997) 3083.

P. Bühlmann, E. Pretsch, E. Bakker, Chem. Rev. 98 (1998) 1593.

J. Bobacka, A. Ivaska, A. Lewenstam, Chem. Rev. 108 (2008) 329.

ISEs are electrochemical sensors

Ion-selective electrodes

O2-sensor (Lambda)

Glucose sensorpH-electrode

- environmental analysis

- clinical analys

• In clinical analysis, ISEs are used all over the world for the

determination of pH, Na+, K+, Li+, Ca2+, Mg2+, Cl- and

CO32- at well-defined concentrations in biological fluids

– Standardized ISEs fulfill a global demand !

• In process analysis, each industry has a different ”wish list”

in terms of species to be monitored and the concentration

range of interest

– ISEs should be developed and tested for each case !

Two different applications of ISEs

E. Bakker, D. Diamond, A. Lewenstam, E. Pretsch, Anal. Chim. Acta, 393 (1999) 11.

K - selective electrode Reference electrode

Sample solution

Ion-selective membrane

Ag/AgCl Ag/AgCl

KCl(3 M)

Potentiometry

ION-SELECTIVE ELECTRODE

Liquid junction

Ag + Cl = AgCl + e- -

Potentiometric response (cationic)

EWhen ni = +1Slope = +59.16 mV / log ai

When ni = +2Slope = +29.58 mV / log ai

2.303logo

RTE E a

detection limit

Potentiometric response (anionic)

2.303logo

RTE E a

detection limit

When ni = -1Slope = -59.16 mV / log ai

When ni = -2Slope = -29.58 mV / log ai

Selectivity of ion-selective electrodes

• The potential of an ion-selective electrode is determinedprimarily by the activity of the main ion (primary ion = i) but also other ions (interfering ions = j) may contribute to the potential.

• The influence of interfering ions is given by the selectivitycoefficient (Ki,j) included in the Nicolsky-Eisenman-equation:

• This equation has some limitations in those cases when the primary (i) and interfering (j) ions have different charge.

,ln( )i jn no

i i j j

RTE E a K a

n F= + +∑

Classification of ion-selective electrodesbased on the type of membrane used

• Glass membranes– for H+ (pH) and certain monovalent cations

• Solid-state membranes based on inorganic saltcrystals

– LaF3, AgCl, AgBr, AgI, Ag2S, CuS, CdS

• Polymeric membranes– hydrophobic polymer membranes containing neutral

or charged carriers (ionophores)

pH-electrodewith glassmembrane

The referenceelectrode is builtinto the same electrode bodyas the indicatorelectrode(combination electrode).

Glass membranes

SiO2 Na2O Li2O CaO Al2O3

72 % 22 % 6 % H+

80 % 10 % 10 % H+

71 % 11 % 18 % Na+

69 % 27 % 4 % NH4+

Cross-section of a pH-sensitive glassmembrane

Calibration curve (pH-electrode)

Solid-state membranes based on inorganic salt crystals

Polymeric membranes

• Plasticized polymer membranes– PVC (33 %)

– Plasticizer (65.5 %)

– Ionophore (1 %)

– Lipophilic ions (0.5 %)

• Plasticizer-free polymer membranes– methacrylic–acrylic copolymers

– covalently bound ionophore / ions

CF3CF3

CF3 CF3

Poly(vinyl chloride)(PVC)

Potassium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]-borate (KTFPB)

Bis(2-ethylhexyl)sebacate(DOS)

Valinomycin

+K ISE

Typical composition

of a K+-selective

membrane :

Pb2+-selective electrode withvery low detection limit

Applications of ion-selectiveelectrodes range from conventionalpH measurements to automatedanalysis on the planet Mars.

pH of rainwater (year 2001)

pH-sensitive fieldeffect transistor

Solid-contact ISEs and CHEMFETs can be miniaturized

The ”Chem 7” test

Na+, K+, Cl-, total CO2glucose, urea, creatinine

constitutes up to 70 %

of the tests performed

in the hospital lab.

•Mg2+

•NH4

•ClO4

•NO3

•Silver/Sulfide

•Cadmium

•Pb/Cu/Zn/Fe - via ASV

•Cyclic Voltammetry

•ORP (redox potential)

•Temperature

•Conductivity

•pH (3 sensors)

•Li Reference (3 sensors)

•Dissolved O2

•Dissolved CO2

•Cl- (2 sensors)

•Br-

•Na+

•Ca2+

2007 Phoenix Mars Scout mission

Automatic analysis on the planet Mars !

K - selective electrode Reference electrode

Sample solution

Ag/AgCl Ag/AgCl

KCl(3 M)

Potentiometry

ION-SELECTIVE ELECTRODE

Liquid junction

Conventional ISE(liquid-contact ISE)

Solid-contact ISEs are more robust

Inner reference electrode& inner solution

Conductingpolymer

- First article published in 1992- Innovation Prize in 2001- Commercial products emerging

https://www.abo.fi/student/analytisk_kemi

ELECTROACTIVE MATERIAL

(polythiophene)MEMBRANE /

SOLUTION

(ionic conductor)

or otherelectronicconductor

polaron

bipolaron

Electrochemical oxidation (p-doping)

Conjugatedpolymer Electrolyte

Electronicconductor

Oxidized (p-doped) conjugated polymer

Conjugatedpolymer

Electronicconductor

Electrolyte

Potentiometric response of

conducting polymers

[ ][ ]Red

FRTconstE +=

[ ]−−= XconstEF

RT ln''

[ ]++= MconstEF

RT ln'''

SubstrateConductingpolymer Solution

A. Lewenstam, J. Bobacka, A. Ivaska, J. Electroanal. Chem. 368 (1994) 23.

J. Bobacka, Z. Gao, A. Ivaska, A. Lewenstam, J. Electroanal. Chem. 368 (1994) 33.

Solid-contact ISE

SubstrateConductingpolymer Solution

Ion-selectivemembrane

A. Cadogan, Z. Gao, A. Lewenstam, A. Ivaska, D. Diamond, Anal. Chem. 64 (1992) 2496.

Poly(3,4-ethylenedioxythiophene)

(PEDOT)

Stable conducting polymer !

G. Heywang, F. Jonas, Adv. Mater. 1992, 4, 116 .

Solution-casting of

PEDOT and ISM

Insulating layer

Alumina

Insulating layer PEDOT(PSS)

(Baytron P)

Screen-printed

substrates

M. Vázquez, P. Danielsson, J. Bobacka,A. Lewenstam, A. Ivaska,Sens. Actuators B, 2004, 97, 182.

Radial

flow cell

M. Vázquez, J. Bobacka, A. Ivaska, A. Lewenstam, Talanta, 2004, 62, 57.

Ion-selective microelectrodes

Electrode substrate

Conducting polymer

Capillary glass

Polyethylene

Mercury

Epoxy glue

Electrode substrate

Conducting polymer

Capillary glass

Polyethylene

Mercury

Epoxy glue

Electrode substrate

Conducting polymer

Capillary glass

Polyethylene

Mercury

Epoxy glue

Mikael Södergård

PSS-K+

Solution

e-Ag / AgCl

PlasticizedPVC

Solution

PlasticizedPVC

Inner solution

Pt, Au, C

Cond.polymer

Pt, Au, C

Funct.cond.polymer

Conventional ISE Solid-contact ISE

Functionalized

conducting polymer

”Three generations” of ISEs

Many conducting polymers

have been applied as

ion-to-electron transducers

and/or

sensing membranes

solid-state ISEsNH2

H3C CH3

NH2 OH

(1) (2) (3)

(4) (5) (6)

(7) (8) (9) (10)

(12) (13)

(14) (15)

Review:J. Bobacka, Electroanalysis

2006, 18, 7.

GC / SWCNT / KClaq

G.A. Crespo, S. Macho, J. Bobacka, F.X. Rius, Anal. Chem. 81 (2009) 676.

Rs = solution resistanceCd = bulk capacitanceZD = finite-length Warburg diffusion

ISEs using conjugated polymers as

solid contact

• Good long-term stability

– Gyurcsányi & Lindner et al., Talanta, 63 (2004) 89.

– Hall et al, Anal. Chem. 76 (2004) 2031.

• Low detection limit (< 10-9 M)

– Bakker & Pretsch et al., Anal. Chim. Acta 523 (2004) 53.

– Maj-Zurawska & Lewenstam et al., Anal. Chem. 76 (2004)6410.

• Single-use sensors

– Michalska & Maksymiuk, Anal. Chim. Acta, 523 (2004)97.

• Polyaniline-based pH nano-electrode

– Ogorevc & Wang et al., Anal. Chim. Acta, 452 (2002) 1.

• Polypyrrole-based NO3- sensor

– Bendikov & Harmon, J. Chem. Edu. 82 (2005) 439.

• Conjugated polymer-based Ag+ sensors

– Vázquez & Bobacka et al., J. Solid State Electrochem. 9(2005) 312.

• Conjugerade polymers doped with complexingligands

– Migdalski & Lewenstam et al., Polish J. Chem. 78 (2004)1543.

ISEs using conjugated polymers as

selective membrane

0 10 20 30 40 50

precipitation

starts

Vtartaric acid

CH3COOH

Titration of trimeprazine base with tartaric acid in

isopropanol using GC/PANI as indicator electrode

The ”new wave” of ISEs

• Low detection limit

• Solid-contact ISEs

• Solid-state reference electrodes

• Plasticizer-free membranes

• Covalently bound ionophores

• Advanced non-equilibrium models

J. Bobacka, A. Ivaska, A. Lewenstam, Chem. Rev. 108 (2008) 329.

Solid-state ion sensors and

solid-state reference electrode

2. Ion-to-electron transducer

3. Ion-selective membrane

1. Electronic conductor

All-solid-state ISE

2. Ion-to-electron transducer

3. Equitransferent membrane

1. Electronic conductor

All-solid-state

reference electrode

E / mV

Signal interpretation

Low detection limit

Miniaturization

Sensor materials

SC-ISEs & SC-RE

pH-ISE

Pb2+-ISE

Referenceelectrode

Au / PEDOT / PVC-based membrane *

* pH-ISE: PVC + oNPOE + H II + KTpClPB

Pb2+-ISE: PVC + DOS + Pb IV + NaTFPB

Reference electrode: PVC + oNPOE + TBATBB

Electrode body designed by:J. Migdalski and B. Bas,

AGH University of Science and Technology, Cracow, Poland

Solid-contact pH-ISE vs. SC-RE

0 1 2 3 4 5 6 7 8 9 10 11 12 13

V Slope = 58 mV/dec

Solid-contact Pb2+-ISE vs. SC-RE

-13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1

log aPb2+

Slope = 29.6 mV/dec

LOD = 10-7.3

Simultaneous measurement of Pb2+ and pH

in environmental water samples

pH-ISEs

Pb2+-ISEs

Referenceelectrode

S. Anastasova-Ivanova, U. Mattinen, A. Radu, J. Bobacka, A. Lewenstam, J. Migdalski, M. Danielewski, D. Diamond, Sens. Actuators B, 146 (2010) 199–205.

� Speciation of lead

� pH measurements

Detection limit = ca. 2 ppb

• J. Bobacka, A. Ivaska, A. Lewenstam, Electroanalysis, 15

(2003) 366.

• J. Bobacka, T. Lindfors, A. Lewenstam, A. Ivaska, American

Laboratory, 36 (2004) 13.

• J. Bobacka, Electroanalysis, 18 (2006) 7.

• J. Bobacka, A. Ivaska, A. Lewenstam, Chemical Reviews, 108

(2008) 329.

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