diff sampler

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ANALISIS PENCEMAR LINGKUNGAN

Diffusive SamplerDiffusive or passive samplers are known as the cheapest method of monitoring

air quality and can give a good overall picture of average pollutant levels in an area. The

low cost per tube permits sampling at a number of points in the area of interest. Although

results from single point passive samplers are not as precise as those from automatic

point monitors, the accuracy and reproducibility of the measurements has increased over

recent years.

Diffusive samplers are typically clear plastic tubes open, or with a membrane

screen, at one end and a pollutant-absorbing chemical matrix or gel at the closed end. Thediffusion tube collects the pollutant during the exposure period (one week or more), at the

end of which the tube is returned to an analytical laboratory. The time resolution of this

technique is limited, as it can only provide information on integrated average pollutant

concentration over the exposure period. They have been widely used for many years in

personal monitoring and occupational health assessments (Dore and McGinlay, 1997).These kind of devices are very appropriate for gas flux emission measurement,

they do not require another measurement and can be applied over a wide area, because of

their low cost. One disadvantage of these devices are that they still require furtheranalysis in laboratory.

Theoretical understanding of gas movement in diffusive samplers have been

introduced by Palmes, et.al in 1976. For the axial tube type diffusive sampler, the rate of

mass transfer down the concentration gradient induced in the air gap, can be derived fromthe Ficks first law (Bates, et.al, 1997):

where:

dm/dt = rate of mass transfer

d = diffusion coefficient of gas

dc/dx = concentration gradient along the axisIntegration of the above equation gives:

where:mt = mass transferred in time t

dxdCDA

dtdm =

)( 0 at CC

l

DA

t

m=


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Besides the axial tube type sampler described above, to increase the uptake rate of

gases, the radial type sampler has been introduced. Again Ficks first law may be used todescribe the transfer across the still air zone. In cylindrical coordinates the equation

becomes:

where r = radiush = length of the cylinder

dC/dr = concentration gradient along the radius

The integrated form is follows:

Several types of diffusive sampler now commercially available. They can be tubeor badge type, pollutant can be chemically bound by appropriate reagent or physically

adsorbed by inert media. For further analysis the pollutant may be extracted by thermal

desorption or solvent extraction. Various types of diffusive sampler can be seen in

appendix 2.

Adsorbent For Gases

Silica gelSilica gel is one of the synthetic amorphous silicas, It is rigid and forms a

continuous network of spherical particle of colloidal silica. It is synthesised by following

reaction:

Na2SiO3 + 2HCl + nH2O 2NaCl + SiO2.nH2O + H2O

Its properties e.g. surface area, pore volume and strength can be varied by

varying the silica concentration, temperature, pH and activation temperature. Silica gel

(along with activated alumina) is a desirable sorbent for drying because of its high

f d i f ti At l f th t l l

dr

dCrhD

dt

dm2=

a

at

rr

CChD

t

m

0

0

ln

2

=


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- aldehyde

Activated carbonThe surface properties of activated carbon is non-polar or only slightly polar as a

result of the surface oxide groups and inorganic impurities. This properties give the

following advantages:

- can be used to perform separation and purification processes without priorstringent moisture removal.

- it adsorb more non-polar and weakly polar organic molecules than othersorbents do

- the heat of adsorption is generally lower than other sorbents so that strippingof the adsorbed molecules is easier.

It has a large surface area 300-2500 m2/g which is the largest among all sorbents.

For application in liquid phases, it should have pore size near or larger than 30 A,whereas for gas phases the pore diameter in the range from 10 A to 25 A. According to

IUPAC, the pores are subdivided by diameter (d)

- macropores (d>500 A)- mesopores (20 A


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Activated alumina is a dehydrated (or partially) alumina hydrates, both crystalline

and amorphous with high surface area. It has the greatest affinity for water, and is appliedin drying of gases and liquids because of its hydrophilic property and large surface area.

It has been applied as a sorbent for drying gases: Ar, He, H2, alkanes (C1-C3),hydrocarbon, Cl2, HCl, SO2, and NH3. It also may be used for the removal of various

contaminants from gases, such as trace fluorides, cloride, H2S, alcohol and ethers.

Molecular sieve carbonMolecular sieve carbon (MSC) is less hydrophilic than zeolites, so can be used

more efficient in separation process involving wet-gas streams. It has been used for the

production of nitrogen from air.

In the preparation and sieving properties study, three approaches were taken:a. Carbonization of polymers such as poly vinylidene chloride (PVDC); saran

(90/10 mixture of vinylidene chloride and vinyl chloride); and cellulose, sugar

and coconut shell.

b. Slightly carbonizing coals, especially anthracites

c. Coating of the pore mouth of the commercial activated carbon with acarbonised or coked thermosetting polymer.

Direct Reading Colorimetry Detector TubeColorimetry detector tube or direct reading diffusive sampler is a simple device

that capable to analyse the airborne contaminant quantitatively based on coloration of

indicating layer. When the molecule of airborne contaminant reach the reagent layer they

react chemically with the filling material causing a colorimetric stain. The residual stainlength is a measure of the dosage of the contaminant to be measured, i.e. the product of

concentration and time.

Molecules of air contaminants migrate into a diffusive sampler according to the

laws of gaseous diffusion. When the sampler is exposed in air a concentration gradient isdeveloped between the ambient air and the air inside the sampler.This phenomenon can

be described by Ficks first law of diffusion as described previously.

Because of a gas molecule react with the impregnated chemicals, there are

virtually no free gas molecule in the air inside the sampler. The full concentrationdifference is thus available as a driving force for diffusive sampling. However the

diffusion pathway for the gas molecule becomes longer as the stain gets longer. It ismean, according to Ficks law, that the mass flow decreases with increasing stain length.

The increase of the stain length (dl) can be formulated by

d


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2/1

2

=

ikctDl

The validity of above relationship can be demonstrated by the calibration curve of the

direct-reading diffusive sampler using scale figures for the dosage of the contaminant to

be measured (May, 1989).

Due to the air movement only depending on diffusion of gases, then a passivedetector tube can be imagined as long term sampler. The problem associated with this

kind of device is the flow rate of gas can be too low for the reagent system used becauseside reactions can occur on long contact of the gas with the indicating layer.

For satisfactory function, the reagent must fullfil the following requirements

((Leichnitz, 1976):1. the indication color must be a measure of the absolute amount (mass) of gas

(product of concentration and air sample volume must be constant).

2. the absorption capacity of the reagent must not be affected by humidity changesand must remain constant during the measuring process.

3. The rate of reaction of the gas with the reagent system must be much higher thanthe rate of any side reaction with may take place on the surface of the reagentcarrier In many detector tubes, the calibration curve can be represented by the

following equation:

where:

l = length of the discolorationm = mass of gas which has reacted in the tube,

A = constant with the dimension of reciprocal time

C = sorption capacity of the indicating preparation

v = flow by volume of air sample in the tube.

Indicating Layer Material for Detector TubeThe supporting material for the indicating layer in the tube may be silica gel,

alumina, ground glass, pumice, or resin (Jungreis, 1985). The indicating layer or thereagent system comprises of one or more chemical compound which can produce a

colour change when react with target contaminant.

)1( /1vA

eA

v

C

ml

+=


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Ozone (O3)

The indicating layer contains indigo compound which changes colour from blue tocolourless due to oxidation by ozone.

O3 + Indigo (blue) Isatine (colourless)

Chlorine and nitrogen dioxide also discharge the color of indigo when present in

concentration higher than 5 ppm.

Sulphur dioxide (SO2)The indicating reaction for measurement of sulphur dioxide in the various detector tube

may involve formation of the extremely stable anion complex [Hg(SO3)2]2-

. Theindicating reagent is composed of disodium tetra chloromercuriate and methyl red.

Hydrochloric acid liberated during the reaction changes the indicator color.

2SO2 + Na2[HgCl2] + 2H2O Na2[Hg(SO3)2] + 4 HCl

The second principle that can be used for sulphur dioxide detection is reaction of free

iodine with sulphur dioxide (decolorizing the blue iodine-starch complex)

SO2 + I2 + H2O SO42-

+ 2I-+ 4H

+

Hydrogen sulphide become serious interferen if use the detector tube without a cupric-containing precleansing layer.

Reactions in Colorimetric Detector TubeSeveral types of chemical reaction that used to generate colour change are:

Oxidation-reduction

Acid-base

Substitution-addition and others

Oxidation-reduction

Example of this type is CO detector tube that created by using reagent a mixtureof iodine pentoxide and fuming sulphuric acid. The iodine is reduced and the carbonmonoxide is oxidised:


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SeO2

I2O5 + H2 S2O7

I2+ Ox.Pr White/Brown-green CO, many organicsI2O5 + H2 S2O7 I2+ Ox.Pr White/Brown-green CO, many organics

I2O5 + H2 SO4 I2+ Ox.Pr White/Brown-green Aromatic hydrocarbon

Cr2O7+H2SO4 Cr3+

+ Ox.Pr Orange/Green Alyphatic Hydrocarbon

Cr2O7+H3PO4 Cr3+

+ Ox.Pr Orange/Green Alcohol

CO + K2Pd(SO3)2 CO2+SO2+K2SO3+Pd Yellow/Green CO specific

R1C=CR2 + Mo6+

Mo3+ + Ox.Pr(splitting of double bond)

Yellow/blue Unsaturated hydrocarbon

Acid-Base Reactions

Many detector tubes use acid-base indicators impregnated on a neutral or buffered

substrate to measure gaseous substance that have acidic or basic properties. Such

compounds are acetic acid, ammonia and amines, carbon dioxide, hydrazine, hydrogenchloride, hydrogen fluoride, nitric acid and sulphur dioxide. As can be seen, these

reactions are not specific, other acids and bases will interfere, particularly strong acids

and bases.

Acid-base indicator used in detector tubeGas/vapour Indicator Colour change

Acetic acid Phenol red Pink/white

Ammonia Bromophenol blue or thymol blue Orange/blue green;

Lavender/pale yellow

Carbon dioxide Thymol blue Blue/pale yellow

Hydrazine Bromophenol blue Yellow/blue

Hydrogen chloride Bromophenol blue or congo red Blue/white; pink/blue

Sulphur dioxide Phenol red or bromocresol green Pink/white; blue/yellow

Other types of reactions

These reactions included addition, substitution or mixtures of these. Some typesare fairly specific for one compound. For example, the substitution reaction of carbonylcompounds with dinitrophenyl hydrazine, addition reaction of chlorine with

tetraphenylbenzindine. The reaction can be simply one stage reaction or two stages ormore.

For some gases, because of their stability, it is not possible to obtain directly a colour


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Reaction Colour change Specificity

Substitution

H2S + PbAc2 PbS + 2Hac White/black Specific

R1R2C=O + H2NNHC6H3(NO2)2

R1R2C=NNHC6H3(NO2)2 + H2O

Dinitrophenylhydrazine hydrazone

Pale-yellow/

yellow

Specific for carbonyls

Addition

Cl2 + TPB Cl-TPB-Cl

Tetraphenylbenzidine quinoidimonium saltWhite/blue Fairly specific

Combination

2C6H6 + CH2O C6H5CH2C6H5 + H2O

+2H2SO4

3H2O + SO2 + C6H5CH= =O

paraquinoid compound

White/brownSpecific for aromatics (or

aldehydes)

Using strong oxidant

Chlorinated hydrocarbons + KMnO4 +

H2SO4(conc) Cl2

Cl2 + TPB Cl-TPB-Cl

White/blue Nonspecific

Using heat to break down

compoundCCl4 + heat Cl2

CH3CN + heat NO2

CF2Cl2 + heat Cl2

White/blue nonspecific

From the literature review, the first task identified was to prepare a sensitivedetector system for nitrogen dioxide (NO2).


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Appendix 1

Various types of diffusive samplers

a. Thermal desorption passive samplerThis sampler is usually used for organic vapour and un-reactive pollutants. The sampler can be radial or axial type. The filling material for

trapping the gases may be molecular sieve, activated charcoal, graphitized carbon black etc.


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b. Solvent desorption passive sampler.This type of sampler commonly uses for inorganic gases: NO, NO2, NOx , SO2, O3, NH3 etc. Reagent used depends on the target gases. The

support material can be paper, glass fibre, etc.


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Appendix 3

Various type colorimetric detector tube


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Appendix 4

Diffusive sampler for greenhouse gases

NITROGEN DIOXIDE PASSIVE SAMPLER (NO2)No Type Dimension Chemistry of active material Method of analysis Ref

1 Badge (Ferm) D: 24 Whatman filter paper coated with a solution of NaOH and NaI in

methanol

Spectrophotometry (540nm: nitrite)

after mixing with diazotizing

reagent.

8

2 Badge (Willems) D: 28 Whatman GF-A glass fibre filter impregnated with a solution of

triethanolamine-acetone.

FIA_ Spectrophotometry (540nm:

nitrite) after mixing with

diazotizing reagent (Saltzman

method)

9

3 Badge (Ogawa) D: unknown Impregnated-cellulose fibre filter (unknown chemicals) FIA-Spectrofotometry (545nm:

nitrite)

10

NITROUS OXIDE PASSIVE SAMPLERNo Type Dimension Chemistry of active material Method of analysis Ref

1 Badge (RS

Landauer)

Unknown Molecular sieve Thermal desorption and than

analysed by IR

11

2 Tube with stainless

screen

L:55; D:4 Molecular sieve 5A (60/80 mesh, Supelco) in glass tube Partially desorption in vial,

measurement head space by GC

with EC detector

12

SULPHUR DIOXIDE PASSIVE SAMPLERNo Type Dimension Chemistry of active material Method of analysis Ref

1 Badge (Toyo Roshi

Kaisha)

Unknown Filter paper impregnated with tetraethanolamine (TEA) SO2 absorbed was oxidized to SO4

by H2O2; SO4 was analyzed

spectrophotome-trically (662)

13

2 Badge (Ferm) D: 24 Whatman filter paper coated with a solution of NaOH (dissolved in Ion chromatography 8


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small water) in methanol

3 Badge Unknown Potassium Carbonate Ion chromatography 14,154 Badge (Ogawa) D: unknown Impregnated-cellulose fibre filter (unknown chemicals) Ion Chromatography 10

OZONE PASSIVE SAMPLERNo Type Dimension Chemistry of active material Method of analysis Ref

1 Diffusion tube in

protective box

L:74; D:10 Glass fibre filter coated with a solution of 1,2-di(4-pyridyl)ethylene

(6%m/v) in acetic acid (75%), ethylene glycol (15%); reaction withmethylbenzothiazoline hydrazone (MBTH)

Spectrophotometry (442 nm) 16

2 Indigo papers under

shelter

D: 50 Indigo on filter paper buffered to pH 2.2; extraction of isatin with

ethanol

Spectrophotometry (408 nm) 16

3 Diffusion tube L:240 D:30 Indigo on filter paper unbuffered; extraction of isatin with ethanol Spectrophotometry (408 nm) 16

4 Badge under shelter

(poor correlation)

D:50 Potassium Iodide on filter paper; Ion Chromatography 16

5 Petridisk under

shelter (poor

correlation)

D:50 Potassium Iodide-starch solution on filter paper; Spectrophotometry (575 nm)16

6 Badge sampler

(Ogawa & Co)

Filter coated with a nitrite-based solution Ion Chromatography 17

7 Badge sampler

(CSIRO Australia)

D:25 Impregnated filter (unidentified) Ion Chromatography 18

AMMONIA PASSIVE SAMPLERNo Type Dimension Chemistry of active material Method of analysis Ref

1 Open Tube D: 10.9 L:71.2 Unknown FIA- Conductometric detection 19

2 Tube with a

stainless steel grid

in the inlet

D: 10.9 L:71.2 Unknown FIA- Conductometric detection 19

3 Tube with per-

meable membra-ne

in the inlet

D:10.9 L:35.6 Unknown FIA- Conductometric detection19

4 Badge, with a D:28 Tartaric acid applied to a glass fibre filter disc FIA- Conductometric detection 19, 20


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Teflon filter

5 Badge, with amembrane inlet

Unknown Impregnated filter with citric acid FIA/Indophenol 21

6 Badge with teflonfilter (5um)

Unknown Stainless steel grid with phosporic acid Ion chromatography21

7 Badge with

membran inlet

Unknown Impregnated filter with phosporic acid Indophenol21

Badge with teflon

filter

Unknown Impregnated glass surface with Phosphoric acid Ion Chromatography 21

8 Palmes type with

membran

Unknown Stainless steel grid with sulphuric acid Conductance 21

References:

1. K Leichnitz,Ann.Occup. Hyg., 19, 1976, pp 159-1612. ED Palmes, AF Gunnison, J DiMattion, and C Tomczyk,AIHA Journal, 37, 1976, pp 570-5773. E Jungreis, Spot Test Analysis: Clinical, Environmental, Forensic and Geochemical Applications, John Wiley & Sons, New York, 19854. CJ Dore and J McGinlay, In: Air Pollution in The United Kingdom, edited by G Davison and CN Hewitt, Royal Society of Chemistry, 19975. WJ May,Ann.Occup.Hyg., 33, 1, 1989, pp 69-786. M Bates, N Gonzales-Flesca, V Cocheo and R Sokhi,Analyst, 122, 1997, pp1481-14847. DA Skoog, DM West and FJ Holler, Fundamental of Analytical Chemistry, 7nd Ed, 1996, Saunders College Publishing, London8. GP Ayers, MD Keywood, R Gillett, PC Manins, H Malfroy and T Bardsley, Atmospheric Environment, 1998, 32, 20, pp 3587-35929. AH Gustafsson, R Lindahl, JO Levin and D Karlsson, J. Environ. Monit, 1999, 1, pp 349-35210.Ogawa & Co., NO, NO2,Nox and SO2 sampling protocol using Ogawa sampler, 4

thEd., 1998

11.OSHA,Nitrous oxide in workplace atmosphere (passive monitor), 1994, OSHA Salt Lake Technical Center, Salt Lake City USA12.S Kumagai and S Koda,Am. Ind. Hyg. Ass. J, 1999, 60, 4, pp 458-46213.Y Yang, XX Zhang, T Korenaga, K Higuchi, Talanta, 1997, 45, pp 445-450


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14. M Ferm,A sensitive diffusional sample, 1991, IVL-Report B-1020, Gothenburg

15. M Hangartner,Diffusive sampling as an alternative approach for developing country, World Conggres on Air Pollution in DevelopingCountries, 1996, Costa Rica

16. M Hangartner, M Kirchner and H Werner,Analyst, 1996, 121, pp 1269-127217. Anonymous, Protocol for Ozone Measurement Using The Ozone Passive Sampler Badge, 1994, Rev.2, Harvard School of Public Health,

Dept. of Environmental Health, USA

18.CSRIO Website,Atmospheric Research, http://www.csrio.edu.au19.Th R Thijsse, JH Duyzer, HLM Verhagen, GP Wyers, A Wayers and JJ Mols,Atmospheric Environment, 1998, 32, 3, pp 333-337

20.JJ Willems, P Hofschreuder,In Air Pollution Research Report 37, Eds. I Allegrini, A Febo, and C Perrino, 1990, pp 113-11821.M Kirchner, S Braeutigam, M Ferm, M Haas, M Hangartner, P Hofschreuder, A Kasper-Giebl, H Rommelt, J Stiedner, W Terzer, L Thoni,H Werner, and R Zimmerling, J Environ. Monit, 1999, 1, pp 259-265

22.RT Yang, Gas separation by adsorption processes, Imperial College Press, 1997 London

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