Carson Ph., Mumford C. Hazardous Chemicals Handbook (Справочник по опасным химическим веществам)

Подождите немного. Документ загружается.

the test sample is aspirated into a flame where chemical reduction of metal ions to metal atoms

occurs. Light is emitted at the discrete absorption wavelength for the metal. A disadvantage is the

need for a separate lamp for each element. Emission spectrometry is therefore preferred. Here test

material is heated and vaporized using a DC or inductively-coupled plasma generator, after which

an optical emission spectrum as a function of wavelength is recorded. An advantage of this

technique is that a range of metals or metalloids can be analysed simultaneously.

Chemiluminescence

Here a chemical reaction produces a molecule with electrons in an excited state. Upon decay to

the ground state the liberated radiation is detected. One such example is the reaction between

ozone and nitric oxide to form nitrogen dioxide emitting radiation in the near infra-red in the

0.5–3

region. The technique finds use for measuring nitric oxide in ambient air or stack emissions.

Chromatography

This technique permits the separation of a mixture of compounds by their partition between two

immiscible heterogeneous phases, one of which is stationary. It detects substances qualitatively

and quantitatively. The chromatogram retention time is compound-specific, and peak-height indicates

the concentration of pollutant in the sample. Detection systems include flame ionization, thermal

conductivity and electron capture. With gas chromatography the mixtures to be separated are in

the vapour phase under the operating conditions of the equipment. A gas is used as the mobile

phase to carry the sample over a column of stationary phase. Flame ionization detection operates

by ionisation of molecules in a hydrogen flame and detection of the current change using a pair

of biased electrodes. The current signal is directly related to the number of carbon atoms in the

sample. Thermal conductivity detectors measure the change in electrical resistance of a heated

filament as gas flows over it. It is most suitable for gases with very high, or very low, conductivity.

Traditionally gas chromatography is a laboratory analysis but portable versions are now available

for field work.

In classical liquid chromatography a solution of solute percolates under gravity through a

column packed with finely-divided solid when different compounds elute at different rates. In

high-performance liquid chromatography (HPLC) the liquid is eluted from a packed column

under high pressure using solvent. Detection systems include differential refractive index, diode

array, electrochemical and ultra-violet-visible absorption. HPLC is used for analysis of less

volatile compounds in liquid samples than those in gas chromatography.

Because of its sensitivity (<1 ppm), ion chromatography has become extremely popular for

analysis of ions in solution. It is a column-based method for separating ions similar to HPLC but

using ion exchange columns and either high- or low-conductivity eluent. The most common

detectors are electrical conductivity and ultra-violet absorption. It finds wide use in air pollution

monitoring of rain waters, impinger solutions and filter extracts for anions such as sulphate,

nitrate, chloride, and cations, including ammonia and metals.

Colorimetry

Use is made of colour changes resulting from reaction of pollutant and chemical reagents: colour

intensity indicates concentration of pollutant in the sample. Reaction can take place in solution or

on solid supports in tubes or on paper strips, e.g. litmus or indicator paper. Quantitative assessment

of colour formation can also be determined using visible spectroscopy. Instruments are calibrated

GASES AND VAPOURS 309

310 MONITORING TECHNIQUES

such that colour intensity is directly related to concentration of contaminant in the test sample.

Arguably the technique could also embrace simple acid-base titrations which utilize colour indicators

to determine the end-point.

Electrochemical techniques

In electrochemical cells sample oxidation produces an electric current proportional to the

concentration of test substance. Sometimes interferences by other contaminants can be problematic

and in general the method is poorer than IR. Portable and static instruments based on this method

are available for specific chemicals, e.g. carbon monoxide, chlorine, hydrogen sulphide.

Coulometry measures the amount of current flowing through a solution in an electrochemical

oxidation or reduction reaction and is capable of measuring at ppm or even ppb levels of reactive

gases. Thus a sample of ambient air is drawn through an electrolyte in a cell and the required

amount of reactant is generated at the electrode. This technique tends to be non-specific, but

selectivity can be enhanced by adjustment of pH and electrolyte composition, and by incorporation

of filters to remove interfering species.

Ion-selective electrodes are a relatively cheap approach to analysis of many ions in solution.

The emf of the selective electrode is measured relative to a reference electrode. The electrode

potential varies with the logarithm of the activity of the ion. The electrodes are calibrated using

standards of the ion under investigation. Application is limited to those ions not subject to the

same interference as ion chromatography (the preferred technique), e.g. fluoride, hydrogen chloride

(see Table 10.3).

Table 10.3 Examples of applications of ion-selective electrodes

Electrode Measurement range (ppm) Major interference

Ammonia 0.01–17 000 Ionic – none

Bromide 0.08–80 000 CN

–

, I

–

, S

– –

Chloride 0.35–3500 CN

–

, I

–

, Br

–

, S

– –

Cyanide 0.003–2600 I

–

, S

– –

Fluoride 0.02–1900 OH

–

Iodide 0.013–127 000 CN

–

, S

– –

Nitrate 0.6–62 000 I

–

, Br

–

, SCN

–

ClO

–

Sulphide 0.32–32 100 Ag

, Hg

Infra-red spectroscopy

The basis of this technique is absorption of IR radiation by molecules over a wide spectrum of

wavelengths to give a characteristic ‘fingerprint’ spectrum providing both qualitative and quantitative

data on the substance. This versatile technique owes its success in occupational hygiene to the

development of a portable spectrometer of the non-dispersive type which focuses on specific parts

of the spectrum in which the pollutant shows peak absorption as opposed to scanning the entire

spectrum. Table 10.4 identifies principal absorption peaks for selected gases. One advantage of IR

is that the detector does not ‘react’ with the gases and the major functional components are

protected and easily removed for maintenance. Since IR detection is potentially sensitive to

temperature, the instrument requires approximately 15 minutes to equilibrate prior to use. Water

vapour can seriously affect performance.

Table 10.4 Main IR absorption peaks for selected gases

Chemical Wavelength

(micron)

Carbon dioxide 4.35

Carbon monoxide 4.60

Methane 3.30

Nitric oxide 5.30

Nitrogen dioxide 3.70

Nitrous oxide 4.50

Sulphur dioxide 4.00

Table 10.5 UV wavelengths for selected gases

Gas Wavelength

(nm)

Ammonia 200

Chlorine 280–380

Hydrogen sulphide 200–230

Nitrogen dioxide 380–420

Oxygen/ozone 170

Sulphur dioxide 285

Compound specific analysers

Several instruments are available that are designed to monitor a specific compound rather than a

wide range of substances. The detection system varies according to the pollutant. A selection is

given in Table 10.6.

Mass spectrometry

This technique relies on the formation of ions by various means in a high-vacuum chamber, their

acceleration by an electrical field and subsequent separation by mass/charge ratio in a magnetic

field and the detection of each species. It can be used for both inorganic and organic substances,

be very sensitive, and be of value in examining mixtures of compounds especially if linked to glc.

Usually this is a laboratory technique but portable or ‘transportable’ models are now available.

Ultra-violet spectrometry

Outermost valency electrons in atoms are excited by ultra-violet radiation. The excited electrons

return to the ground state liberating energy by disassociation, re-emission, fluorescence, or

phosphorescence. The level of UV radiation absorbed follows the Beer–Lambert law (page 312).

The peak wavelength for selected gases is given in Table 10.5. Photo ionization detectors (PIDs)

use ultraviolet light to ionize gas molecules such as volatile organic compounds; the free electrons

collected at electrodes result in a current flow proportional to the gas concentration. The lamp

requires constant cleaning and hence may have limited life expectancy.

GASES AND VAPOURS 311

312 MONITORING TECHNIQUES

Particulates

Samples of particulate matter can be subjected to many of the above analytical techniques in

chemical characterization. The following methods are, however, particularly applicable to analysis

of physical characteristics of particulate matter isolated from air sampling.

Mass concentration

Simple gravimetry of the sample is likely to be an integral component of the determination of,

e.g., the concentration of, or exposures to, airborne dust. Care is required to avoid errors arising

from absorption of atmospheric moisture. This can be avoided by using blank filters, by conditioning

the filters in an atmospherically-controlled room, or use of a desiccator.

Automatic aerosol mass concentration can be achieved directly by collecting particles on a

surface followed by use of a piezoelectric or oscillation microbalance, or by β-attenuation sensing

techniques, or indirectly using light scattering. The piezoelectric microbalance contains an

electrostatic precipitator to deposit particles onto a vibrating silica crystal. The change in resonance

frequency is converted into mass concentration using a microprocessor. Oscillating balances

operate on the principle that air at 50°C (to avoid condensation) passes through a filter attached

to the top of a tapered glass tube which vibrates at its natural frequency. As material is deposited

on the filter the oscillation frequency changes directly in proportion to the increased mass. Beta

gauges rely on the principle that when low-energy β particles pass through a material the intensity

of the beam is attenuated according to Beer–Lambert law:

Table 10.6 Selected examples of compound specific instruments

Compound Detection system

Ammonia Coulometry (e.g. Nessler method)

Ion selective electrode

Oxidation to NO

and chemiluminescence

Carbon monoxide Polarography

Infra-red

Chlorine Ultraviolet spectroscopy

Hydrogen chloride Polarography

Ion-selective electrode

Hydrogen fluoride Polarography

Colorimetry

Inorganic cyanides Colorimetry

Ion-selective electrode

Oxides of nitrogen Chemiluminescence

Coulometry

Oxygen Polarography

Paramagnetic susceptibility

Fluorescence

Ozone Ultraviolet spectroscopy

Chemiluminescence

Coulometry

Phosgene Ultraviolet spectroscopy

Phosphorus and its compounds Flame photometry

Toluene Ion-mobility spectroscopy

Total hydrocarbons Flame ionization

Sulphur compounds Flame photometry

Coulometry

UV fluorescence

I = I

–ux

where I and I

are the initial and attenuated beam intensities, u is the mass absorption coefficient

and x is the absorber thickness.

Light scattering

Optical particle counters provide information on the particles present in different size ranges. A

beam of light is collimated and focused onto a measurement cell. Light impinging on a particle

is scattered and reaches a photomultiplier tube and converted to an output proportional to particle

size. Particle size distributions are computed by appropriate software.

Electrostatic sampling

Particles become positively charged by a corona discharge and travel out of the charging chamber

and collect on a substrate such as a microscope slide. Thus, the method is useful for particles

which are to be examined by optical or electron microscopy.

Optical microscopy

This technique is invaluable for measurement of particle size, for counting the number of particles

and for identification of particles by:

• morphology, e.g. by comparison with standard particles, and

• refractive index using polarized light microscopy.

Electron microscopy

With a resolution of 0.01 µm this technique outperforms optical light microscopy (0.1 µm) and

is used, e.g., to examine fine particles such as metal fume. When linked to other facilities such as

dispersive X-ray analysis, quantitative data can be obtained.

X-ray techniques

Crystals produce different diffraction patterns when subjected to bombardment of monochromatic

X-ray sources and thereby provide unequivocal identification of crystalline materials.

In X-ray fluorescence incident radiation induces electronic fluorescent emission in most atoms.

The effects can be used both qualitatively and quantitatively for metals, alloys etc.

Monitoring water quality

Water is essential to man both directly and indirectly through agriculture and industry in which

vast quantities are used for cooling, energy production, irrigation, refrigeration, washing, solvents

etc. Risk of contamination can render water dangerous, unpleasant, or unusable. Point sources of

water pollution include domestic and industrial waste whilst non-point sources include agricultural

and urban run-offs. Analysis of water is important for estimating the nature and concentration of

contaminants and hence fitness for use. Artificial contaminants are mainly of domestic and

MONITORING WATER QUALITY 313

314 MONITORING TECHNIQUES

industrial origin, and are increasing in similarity because of the expanding domestic use of

chemicals (cosmetics, detergents, paints, garden insecticides and fertilizers). Water quality can be

assessed by direct analysis of chemical substances or by indirect effects, e.g. pH, colour, turbidity,

odour, impact on dissolved oxygen content.

Chemical pollutants are classified as inorganic or organic. The former include metals (e.g. Mn,

Fe, Cu, Zn, Hg, Cd, As, Cr), anions (e.g. Cl

–

, SiO

2–

, CN

–

, F

–

, NO

–

, NO

–

, PO

–––

, SO

––

, S

––

), and gases (Cl

, NH

, O

). Methods for the examination of waters and associated

materials published by the UK Department of the Environment are listed in Table 10.7. Selected

methods for metal analysis are summarized in Table 10.8. Sampling protocols are described in,

e.g., BS 6068 and BS EN 2567. Examples of BS methods for analysis of chemical contaminants

in water are illustrated by Table 10.9. Biological methods are also given in BS 6068.

Monitoring land pollution

Sources of land pollution include transport accidents, spillage during chemical handling, loss of

containment from storage tanks, leakage and landfill of waste effluent. An appreciation of the

processes governing retention, degradation and removal of pollutants and the behaviour of specific

pollutants in soil are essential in devising correct sampling and analytical strategies for assessing

land contamination. Even soil itself varies in dynamics and composition from one site to another.

Constituents include solid phase materials (such as complex mixtures of clays, minerals, organic

matter), liquid aqueous phase of solutions (e.g. natural minerals, fertilizers, pesticides and industrial

wastes) and gaseous phase components (e.g. oxygen, nitrogen, carbon dioxide, oxides of nitrogen,

ammonia, hydrogen sulphide). The determination of toxic elements and organic substances in

soils is a requisite of some EC directives as a means of controlling environmental pollution.

Analyses are important when certain types of waste are recycled, e.g. by spreading sludge from

water purification units on land, composting from household refuse. The choice of analytical

method will be dictated by accuracy, sensitivity etc. Some key techniques are summarized in

Table 10.10 and selected BS methods for monitoring soil quality are listed in Table 10.11.

Monitoring air pollution

Sampling

Differences exist between the monitoring of pollution levels in ambient and workplace air. These

reflect the differences in levels of contaminant, environmental standards, purposes for which data

are used, etc. (see also Table 16.8). Thus, although similarities may exist in detection techniques,

the sampling regimes, analytical details and hardware specifications may differ for assessment of

the two environments. In general, atmospheric levels of contaminants are much lower in ambient

air than those encountered in the workplace. As a result larger volumes of sample are often needed

for ambient air analyses. This can be achieved using pumps of larger flow rate capacities, or by

longer sampling times.

Atmospheric monitoring involves first obtaining samples of the air with subsequent analysis of

the samples collected. Examples of sampling techniques for gases and vapours are given in Table

10.12. Air samples can be pumped into instruments for direct analysis and data readout. Alternatively,

they are collected in air-tight bags, or absorbed in liquids, or onto solid sorbents, for subsequent

laboratory analysis using techniques such as those described on page 308. Common solid sorbents

Table 10.7 Methods for the examination of water and associated materials published by the UK Department of the

Environment

A review and methods for the use of epilithic diatoms for detecting and monitoring changes in river water quality, 1993

Chlorphenylid, Flucofuron and Sulcofuron Waters (Tentative Methods based on methylation and GC-ECD, ion-pair HPLC and

hydrolysis of Sulcofuron to 4-chloro-3-trifluoromethylaniline by GC-ECD), 1993

Cyanide in Waters etc. (by Reflux Distillation followed by either Potentiometry using a Cyanide Selective Electrode or

Colorimetry, or Continuous Flow Determination of Cyanide or Determination by Microdiffusion), 1988

Determination of Aldicarb and other

-methyl carbamates in Waters (by HPLC or Confirmation of total Aldicarb residues and

other

-methyl carbamates in waters by GC), 1994

Determination of the pH Value of Sludge, Soil, Mud and Sediment; and the Lime Requirement of Soil (Second Edition) (by

Determination of the pH Value of Sludge, Soil, Mud and Sediment or by Determination of the Lime Requirement of Soil),

1992

Flow Injection Analysis, An Essay Review and Analytical Methods

Information on Concentration and Determination Procedures in Atomic Spectrophotometry, 1992

Isolation and Identification of Giardia Cysts, Cryptosporidium Oocysts and Free Living Pathogenic Amoebae in Water etc.,

1989

Kjeldahl Nitrogen in Waters [including Mercury Catalysed Method, Semi-automated Determination of Kjeldahl Nitrogen

(Copper Catalysed, Multiple Tube, Block Digestion Method followed by Air Segmented Continuous Flow Colorimetry)

Determination of Kjeldahl Nitrogen in Raw and Potable Water (Hydrogen Peroxide, Multiple tube, Block Digestion

Method followed by Manual or Air-Segmented Continuous Flow Colorimetry) Semi-automated Determination of Kjeldahl

Nitrogen (Copper/Titanium Catalysed, Multiple Tube, Block Digestion Method followed by Distillation and Air Segmented

Continuous Flow Colorimetry), Air-segmented Continuous Flow Colorimetric Analysis of Digest Solutions for Ammonia],

1987

Linear Alkylbenzene Sulphonates (LAS) and Alkylphenol Ethoxylates (APE) in Waters, Wastewaters and Sludges by High

Performance Liquid Chromatography, 1993

Phenylurea herbicides (urons), Dinocap, Dinoseb, Benomyl, Carbendazim and Metamitron in Waters [e.g. determination of

phenylurea herbicides by reverse phase HPLC, phenylurea herbicides by dichloromethane extraction, determination by

GC/NPD, phenylurea herbicides by thermospray LC-MS, Dinocap by HPLC, Dinoseb water by HPLC, Carbendazim and

Benomyl (as Carbendazim) by HPLC], 1994

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-

phosphomolybdenum blue method, Phosphorus in Waters and Acidic Digests by Spectrophotometry-

phosphovanadomolybdate method, Ion Chromatographic Methods for the Determination of Phosphorus Compound,

Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination of

Molybdate Reactive Silicon-1-amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acid

reduction method, Pretreatment Methods to Convert Other Forms of Silicon to Soluble Molybdate Reactive Silicon,

Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992

Sulphate in Waters, Effluents and Solids (2nd Edition) [including Sulphate in Waters, Effluents and Some Solids by Barium

Sulphate Gravimetry, Sulphate in waters and effluents by direct Barium Titrimetry, Sulphate in waters by Inductively

Coupled Plasma Emission Spectrometry, Sulphate in waters and effluents by a Continuous Flow Indirect Spectrophotometric

Method Using 2-Aminoperimidine, Sulphate in waters by Flow Injection Analysis Using a Turbidimetric Method, Sulphate

in waters by Ion Chromatography, Sulphate in waters by Air-Segmented Continuous Flow Colorimetry using Methylthymol

Blue], 1988

Temperature Measurement for Natural, Waste and Potable Waters and other items of interest in the Water and Sewage

Disposal Industry, 1986

The Determination of 6 Specific Polynuclear Aromatic Hydrocarbons in Waters [Using High-Performance Liquid

Chromatography,Thin-layer Chromatography], 1985

The Determination of Taste and Odour in Potable Waters, 1994

Use of Plants to Monitor Heavy Metals in Freshwaters [Methods based on Metal Accumulation and on Techniques other than

Accumulation], 1991

MONITORING AIR POLLUTION 315

316 MONITORING TECHNIQUES

Table 10.8 Methods for analysis of metal content of water

Method Comment Sensitivity

Spectrophotometry–Colorimetry One of most useful and versatile 10

–5

to 10

–7

methods but can be time consuming (10

–9

with pre-concentration)

Kinetic analysis (metal ion acts Sensitive, highly selective, only 10

–8

to 10

–9

as catalyst) needs small samples

Atomic absorption

spectrophotometry:

• Flame Simple, versatile; measures total 10

–6

to 10

–7

• Flameless metal content. Knowledge of 10

–8

to 10

–9

interfering effects important.

Flame and spark emission Not very accurate. Gives multi- 10

–5

to 10

–8

spectroscopy element analyses

Neutron activation analysis Specialized, expensive 10

–9

to 10

–10

Ion-selective electrodes Highly selective but insensitive 10

–5

to 10

–6

and imprecise

Polarography: Restricted to electroactive metals

• Conventional 10

–5

to 10

–6

• Modified 10

–6

to 10

–8

Anodic stripping voltametry Applicable to few metals and 10

–8

to 10

–10

dependent on metal speciation

for gases and vapours (Table 10.13) include silica gel, activated charcoal, or organic resins. Silica

gel is most useful for polar compounds whereas charcoal finds wide use for non-polar substances.

Subsequently, the pollutant is generally removed from the solid phase by thermal desorption or by

solvent extraction. The advantages and disadvantages of the two desorption techniques are

summarized in Table 10.14. Their versatility is illustrated by Table 10.15 for use of charcoal.

Pumps vary from large, stationary high-volume versions to pocket-size devices for use in

personal dosimetry when operators wear sampling devices in the form of tubes or badges in lapels

to collect air sampled in their breathing zone. Passive samplers are also available for monitoring

gases and vapours in air. These are inexpensive devices which do not require a mechanical pump

but rely on the concentration gradient between the air and sorbent material and the resultant

molecular diffusion of the pollutant towards the sorbent according to Fick’s law:

Q = DdC/dZ

where Q = molar flux (mol cm

–2

–1

D = diffusion coefficient (cm

–1

C = concentration (mol cm

–3

)

Z = diffusion path length (cm).

Because of the low rates of molecular diffusion, assessment of workplace air quality using

passive samplers usually entails sampling for a working shift, and exposure periods of one to four

weeks tend to be needed to measure concentrations in ambient air.

Gases and vapours

Analyses of gases and vapours tend to utilize the techniques described on page 308. Many of

these methods were traditionally limited to laboratory analyses but some portable instruments are

now available for, e.g., gas chromatography (Table 10.16) and non-dispersive infra-red spectrometry

(Table 10.17).

Table 10.9 Selected British Standard methods for monitoring water quality

BS reference Substance Method

BS 1427 General guide to methods for field and on-site techniques

analysis of water

BS 2690 free EDTA

hydrazine spectrophotometry

silica

cyclohexylamine spectrophotometry

morpholine spectrophotometry

long-chain fatty acids spectrophotometry

BS 6068 mercury flameless atomic absorption

ammonium distillation and titration

ammonium potentiometric

ammonium manual spectometry

phenol index spectrometric

cyanide diffusion at pH6

cyanogen chloride

ammonium automated spectrometry

nitrate spectrometry using

sulphosalicylic acid

inorganically bound total

fluoride digestion and distillation

iron photometric

calcium and magnesium EDTA titrimetric

nonionic surfactants Dragendorff reagent

anionic surfactants methylene blue titration

arsenic, cadmium, cobalt, atomic absorption spectrometry

copper, lead, magnesium, spectrometry

nickel, zinc

arsenic (total) spectrometry

manganese formaldoxime spectrometry

chemical oxygen demand

sulphate barium chloride gravimetry

borate spectrometry

sodium and potassium atomic absorption spectrometry

and by flame emission

spectrometry

selenium atomic absorption spectrometry

aluminium spectrometry

herbicides gas chromatography and mass

spectrometry

organochlorine compounds gas chromatography

dissolved anions (bromide, liquid chromatography

chloride, nitrate, nitrite,

phosphate, sulphate, chromate,

iodide, sulphite, thiocyanate,

thiosulphate, chlorate, chlorite) liquid chromatography

organic nitrogen and gas chromatography

phosphorus

33 elements inductively coupled plasma

atomic emission spectrometry

nitrogen chemiluminescence

mercury enrichment by amalgamation

free and total chlorine titrimetric or colorimetric

chlorophenols gas chromatography

organophosphates gas chromatography

dissolved oxygen iodometry or electrochemical probe

phosphorus spectrometry

MONITORING AIR POLLUTION 317

318 MONITORING TECHNIQUES

chromium atomic absorption spectrometry

hydrocarbon oil index solvent extraction and gas

chromatography

halogenated hydrocarbons gas chromatography

(volatile)

total organic carbon and

dissolved organic carbon

organically bound halogen

alpha and beta activity

suspended solids filtration through glass fibre

electrical conductivity turbidity

BS EN 11732 ammonium nitrogen flow analysis and spectrometry

BS EN 12020 aluminium atomic absorption spectrometry

BS EN 1483 mercury

BS EN 1484 total organic carbon and

dissolved organic carbon

BS EN 12338 mercury enrichment by amalgamation

BS EN 14911 dissolved sodium lithium

ammonium, potassium,

manganese, calcium,

magnesium, strontium, barium ion chromatography

BS EN 25663 nitrogen Kjeldahl

BS EN 26777 nitrite molecular absorption

spectrometry

BS EN 7887 colour

BS EN 1622 odour

BS EN ISO 12020 aluminium atomic absorption spectrometry

BS EN 13395 nitrate and nitrite nitrogen flow analysis and spectrometry

BS EN ISO 9377 hydrocarbon oil index solvent extraction/gravimetry

Table 10.9 Cont’d

BS reference Substance Method

Table 10.10 Common instrumental techniques for soil analysis

Pollutant Method

• Phosphorus or mineral nitrogen Spectrophotometry

• Alkaline earth metals and transition metals Flame atomic absorption spectrometry

• Alkali metals Flame emission spectrometry

• Aluminium, boron, silicon Inductively coupled plasma atomic emission spectrometry

• Lead in soil slurries Electrothermal atomic absorption spectrometry

• Toxic organic compounds High pressure liquid chromatography

One of the most commonly used portable, gas detection systems is based on colour indicator

tubes employed, in the main, for grab sampling. Tubes are available to detect over 300 substances

(Table 10.18) and, using a combination of tubes, a range of concentrations can be measured. The

technique relies on a manually-operated bellows or piston pump to aspirate a fixed volume of

atmosphere through a glass tube containing crystals (e.g. silica gel or alumina) impregnated with

a reagent which undergoes a colour change upon reaction with a specific pollutant or class of

pollutant. The length of stain that develops is proportional to the concentration of contaminant

and the tube is generally calibrated to permit direct read-off in parts per million. Sample lines of

several metres between the pump and tube allow atmospheres to be sampled, e.g., inside vessels. A

smaller number of special tubes (Table 10.18(b)) are available for longer-term monitoring and these