Chapter 1 Introduction Environmental Analytical Chemistry Environmental Analytical Chemistry Chapter 1 Introduction 精品课程

Chapter 1 Introduction

Environmental Analytical

Chemistry

Environmental Analytical Chemistry

Chapter 1Introduction

精品课程



Chemistry

Teaching materials and reference books

Environmental Analytical Chemistry (Second Edition)

环境分析化学 - 但德忠主编分析化学（双语版 )- 大连理工大学分析化学教研室主编



Chemistry

Total mark



Chemistry

Contents

Contents



Chemistry

Key points and Difficulties

Key points Definition and characteristics of environmental analytical chemistry; Basic concepts and definitions of sample, analyte, matrix, qualitative and quantitative analysis.

Difficulty The relationship between qualitative and quantitative analysis;

Environmental science presents some very difficult problems for

analytical chemists.

Key points and difficulties



Chemistry1.1 Definition and characteristics of environmental analytical chemistry

人口、资源、环境是当今社会关注的三大主题定义：它是研究环境污染物的组成、结构、状态以及含量的分析化学的一个新分支，是 21 世纪分析化学的一个重点研究领域。从某种意义上讲，环境科学的发展依赖于环境分析化学的发展。特点：涉及范围广；对象复杂；变异性；定量分析；普遍性、实用性强。 — 摘自《 21世纪的分析化学》（汪尔康主编）

1.1 Definition and characteristics of environmental analytical chemistry



Chemistry1.2 Environmental science and analytical chemistry

Environmental science encompasses 包含 the study

of the whole human environment and in doing so 这样做 makes use of all scientific disciplines科学学科 . In a

vast number of studies the need emerges for information

on the composition of the parts of the environment

concerned. It is not possible for example, to study the

natural transport of substances, as in the water cycle, or

other natural processes, without measurement of the

substances being transported.

1.2 Environmental science and analytical chemistry



ChemistryThe assessment of the depletion of the ozone layer 臭氧层耗尽 requires measurements of the amount of ozone present

just as any investigation of the greenhouse effect demands

measurement on the concentrations of greenhouse gases.

Heavy metals and pesticides （杀虫剂） are substances

whose use and environmental concentrations are now

controlled by legislation 立法 in many countries, which

cannot be enforced 实施 unless the

concentration can be measured. Hence measurements must

be accurate, precise and fully validated.充分验证，完全有效




Chemistry

In some cases it is necessary to know the exact chemical

structure of compounds. Organic compounds, which differ

structurally only in minor and subtle ways在小的和微妙的方式 , can have very different physiological effects 生理效应 and pose very different levels of health hazards

健康危害 . Heavy metals such as lead and mercury are

dangerous pollutants in their inorganic forms. If, however,

they are converted into organo-metallics by either natural

or anthropogenic人为的 action, they are conferred 赋予additionally with lipid solubility 脂溶性 .

.




ChemistryAs a result, their mobility in the human body is substantially

enhanced, and they become much more hazardous.

Two aspects of environmental science which frequently

arise, are requirements for the surveillance 监管 or

monitoring of a particular area or ecosystem. Although

related, and often utilizing the same measurements, the two

concepts are different. Surveillance implies the assessment

and continued observation of a particular system to ensure

that it is ‘health’ and remains so. This is obviously a

difficult problem because every parameter cannot be

identified (识别 ) and continuously checked.




Chemistry On the precept 从技术规则上讲 that the health of the

system is measured by the health of the living organisms

生物体 that it supports, biological monitoring is often

employed. This approach, which is developed more fully

in chapters 12 and 20, selects certain monitoring

organisms to represent the overall system and keeps a

check on their health. This use of biological monitoring

leads on to the general principles of monitoring.

Individual parameters are selected and regularly 定期地assessed by appropriate measurements.




Chemistry

For example, in order to comply with 符合 legislation on

the release of pollutants into the environment, specified

elements or compounds will need to be measured on a

regular basis 定期地 , either in environmental samples,

or for instance in factory discharges 排放物 . Similarly,

in order that 为了 food and drinking water are known to

be suitable for consumption, the monitoring of specified

qualities and particular components will be needed.




Chemistry Some of the most newsworthy aspects of environmental

science are what might be termed ‘pollution incidents’.

These generally involve the sudden release of pollutants

from a point source such as an oil tanker 油轮 , mine

workings 矿山巷道 or factory. Extensive measurements

will be required for the assessment of the short and longer

term effects of an incident, as well as in the forensic task 司法任务 of providing an unambiguous 清晰的

identification of the source of pollution. A high proportion of

the measurements needed in the circumstances outlined

above 以上概述 fall within the realm 范围；王国 of

analytical chemistry.




Chemistry1.3 Analytical chemistry

Analytical chemistry employs physico-chemical

principles to make measurements of chemical species i.e.

atoms, ions, molecules and free radicals 自由基，游离基 . The material collected and subjected to analysis is

know as the sample. It consists of two parts, the analyte

or analytes which are the substances to be determined, and

the rest of the sample which comprises the matrix. The

matrix can exert considerable influence over the way 方式 in which the analysis is carried out and the quality of

the results obtained.

1.3 Analytical chemistry



ChemistryWhere the aim is to identify or detect the presence of a

species qualitative analysis is carried out. The detailed

determination of molecular structure is known as

structural analysis and is regarded as 被认为是 a

specialized form 特殊形式 of qualitative analysis. In

circumstances where the amount of a substance present is

measured, quantitative analysis is used. It is easy to

define different types of analysis, but in practice the

distinctions 区别 are less clear cut. For example, a

qualitative test may involve the use of a reagent which

develops a colour 显色 in the presence of the

analyte.




ChemistryHowever, below a certain concentration or detection limit the

colour will not be detectable. Thus, the qualitative test is

quantitative also in the sense 从… . 意义上说 that it can

only show that the analyte concentration does not exceed a

certain detection limit. Zero concentration of an analyte can

never be demonstrated in practice and does not exist in

principle. It should be noted that the situation with regard to

关于 living organisms is different and it is sometimes

possible to say for a sample that no organisms of a particular

type are present. The framework 框架 within which a zero

result is reported must be very carefully defined.




Chemistry Environmental science presents some very difficult problems

for analytical chemists. Some of the principal factors

underlying 构成… 的基础 these difficulties are listed

below.

1. The range of analyte types is very wide. They vary from

simple inorganic species at one end of the scale 天平 to

complex bio-molecules at the other.

2. Sample matrices [’meitrisiz] are frequently complex and

unknown. They may be solid, liquid or gaseous.

3. Analytes may have to be measured at very low

concentrations , e.g. a few ppb (μg kg-1).




Chemistry

4. Environmental programmes often generate very large numbers

of samples and place a premium （额外）费用 on

automation.

5. Some analyses can only be made at, or very close to, the

sampling site. Readily portable and robust 易便携和强大的analytical equipment or remote sensing devices 遥感设备are thus required.




Chemistry

Review

Review



Chemistry

Self – study exercises

1. Write down the definition and characteristics of

environmental analytical chemistry.

2. What is the principal factors underlying some very

difficult problems to analytical chemists in

environmental analytical?

3. Preview section1.3 - overall analytical process.

Self –study exercises



Chemistry

References

1. Fifield F W, Haines P J. Environmental Analytical

Chemistry (Second Edition). Blackwell Science Ltd, 2000.

2. 但德忠 . 环境分析化学 . 北京 : 高等教育出版社 , 2009.

3. 大连理工大学分析化学教研室 . 分析化学 (双语版 )(国家精

品课程教材 ). 大连 : 大连理工大学出版社 , 2008.

4. 汪尔康 . 21世纪的分析化学（中国科学院研究生教学

丛书） . 北京 : 科学出版社 , 2001.

References



ChemistryContent

Content



Chemistry

Key points and Difficulties

Key pointsSelection of an appropriate method; sampling plan, sample

collection, sample handling and pretreatment ； analytical

measurement ； method validation and quality assurance ； data

assessment and interpretation.

Difficulty Definition of the aim of overall analytical process; Method

validation and quality assurance.

Key points and difficulties



Chemistry1.4 Overall analytical processes The practical sequence of operations which is used to

obtain an analytical result from a sample, is known as the

analytical method. Its constituent [kən'stɪtʃuənt] parts

are often based upon different chemical principles, e.g.

precipitation, distillation, titration. These are called

techniques. An illustrative list 说明性清单 of some

groups of techniques appears in Table 1.1. If relevant and

reliable analytical information is to be obtained in an

environmental investigation more than a mastery of

analytical techniques and method is required.

1.4 Overall analytical processes



Chemistry

Table 1.1 A classification of some analytical techniques

Type Properties measured

Gravimetric Weight of pure analyte or of a stoichiometric compound of it

Volumetric Volume of a solution containing a known amount of a reagent reacting with the analyte

Spectrometric Wavelengths and intensity of electromagentic radiation电磁辐射 emitted or absorbed by the analyte

Mass spectrometric Abundance 丰度 of atomic ions or molecular fragments 碎片 derived from 衍生于 the analyte

Electrochemical Electrical properties of analyte solutions

Chromatographic Physico-chemical properties of analytes following separation

Nuclear or radiochemical

Energy and intensity of nuclear radiations emitted by the analyte

Thermal Physico-chemical properties of the analyte as heat is applied to it



Chemistry It is essential to have a unified view 统一的观点 of the whole

process from the definition of the aims of the investigation through to

the final interpretation and presentation of the results. It is convenient to

do this in a number of stages 阶段 , i.e.

1. Definition of the aims;

2. Selection and development of an appropriate method

3. Sampling plan, sample collection, sample handling an pretreatment;

4. Separations;

5. Final measurement;

6. Method validation 方法验证 ;

7. Assessment and interpretation of results;

8. Safety




Chemistry1.4.1 Defining the aims of an analytical programme This stage is clearly the fundamental one in designing an overall

analytical procedure. Sometimes it is straightforward, as in the

case of monitoring a system to comply with( 符合 , 遵守 )

specified legal requirements. Indeed, it is increasingly common

to find a standard overall procedure also specified. In other

circumstances the problem can be much more difficult. This is

especially so in investigatory or research situations. It may not

even be obvious what measurements are needed, let alone 更何况 the levels of sensitivity, precision and accuracy required. To

define the analytical requirement, unquestionably requires full

consultation 充分协商 between the environmental scientists

and the analytical chemists.




Chemistry1.4.2 Selection of an analytical method

Having defined the aims of the analysis it is possible to

proceed to 着手 the selection of an appropriate method. A

whole range of factors needs to be taken into account in

this selection process. It is as important to avoid ‘over

analysing’ as it is to avoid producing data which are

inadequate in quality or quantity. Some of the important

factors are listed below. These are not in any strict order of

significance as this may change from one situation to

another.




Chemistry1. What is the analyte?

2. Detection limits;

3. Precision;

4. Accuracy;

5. Turn-round time; 周转时间6. Are analyses needed ‘on-site’?

7. Number of samples and any consequent automation;

8. Cost.




Chemistry1.4.3 Sampling, sample handing and pretreatment

Samples must be collected according to a plan which ensures that

they are representative of the original aims. Throughout

subsequent handling and treatment 在后续整个操作处理 they

must remain so. Many variables need to be taken into account

when producing a sampling plan. Obviously the plan must be

consistent with the principles set out 陈述 in sections 1.3.1 and

1.3.2, above. It must be borne in mind that the overall variability

of the results and the precision of the analysis can be significantly

influenced by variations in the compositions of replicate samples,

and that whatever care is taken such variations can never be

entirely eliminated. These variations must be assessed and

allowed for.




Chemistry At the initial stage of formulating a plan 制定某个计划 as

much information as possible about the proposed sampling

location must be sought. If little is available a pilot study 初步研究 may well be justified 证明合理 before any

hypothesis can be generated.

Sampling can be divided into following types:

Hypothesis guided sampling （假设引导性采样） , which

employs the combined technical expertise 专业知识 of the

environmental scientists and the analyst, is frequently used.

Judgements are made about likely analyte distributions in an

attempt to focus the programme efficiently on to the

established objectives.




Chemistry Random sampling can be usefully applied if no obvious

patterns of analyte exist. The essence 本质 , from the

statistical point of view, is that all blocks 街区 or containers

have the same chance of being sampled.

A practical form of random sampling for a surface, is to

collect samples along the lines of a ‘W’ pattern across the

sampling area. This approach is useful in initial surveys, and

provides a reasonable [ˈri:znəbl] 合理的 chance of obtaining

information on the general distribution 总体分布 of an

analyte while limiting the total number of samples.




Chemistry

Systematic sampling involves collecting samples

according to a rigid 严格的 , predetermined 预定的 plan

with respect to 关于，同…有关的 e.g. location, time

depth. It assumes no previous knowledge with regard to

analyte distribution, or indeed a particularly well-developed

hypothesis. The results should be free from bias 无偏见

but typically, large numbers of samples are generated, and

this may lead to a programme that is expensive to

implement [ˈɪmpləmənt] 实施，执行 .




Chemistry

Stratified sampling may be employed in circumstances

where the system to be studied contains a number of regions

层，界 that are distinctly different. For example in a study

involving depth, the strata are selected on the basis of depth

and random sampling carried out within each stratum.




ChemistryStratified sampling in vertical profile of soil




ChemistryStratified sampling in horizontal profile




Chemistry




Chemistry




Chemistry Continuous monitoring demands a continuous analytical

signal from the sample. Its use is exemplified by the monitoring

of a waste discharge 排废 from a factory or the quality of water

in a river or stream. The need for the continuous signal places

restrictions on 限制 the nature 性质 of the analytical

procedure used. Methods based on batch processes 成批处理

such as chromatography 色谱法 are unsuitable whereas those

derived from electrical 电学的 or spectroscopic 光谱学的

signals have more promising 有希望的 characteristics. The

practical situation is best illustrated by considering some typical

examples.




Chemistry In a land survey for a particular analyte, both lateral

[ˈlætərəl] 横向的 and vertical variations in concentration need to

be assessed. A routinely used approach is to divide the study area

with a regular grid pattern 网格 , taking samples at the centre of

each grid square and at predetermined 预定的 depths. The

dimensions 尺寸 of the grid will clearly be related to the size of

the area to be covered. For relatively small sites such as industrial

ones, 10 m squares may be appropriate. On the geochemical

scale, 1 km squares are more likely, with a more detailed study to

follow, if an initial, large-scale 大比例尺的 survey, indicates

local areas of interest. In completing the picture, other attributes

of the site might be examined, such as groundwater, streams or

vegetation.




ChemistryFinally, temporal [ˈtempərəl] 时间的 variations and the effects

of the seasons need to be borne in mind. For example, nitrate

concentrations will depend on the stage of the agricultural cycle

at which nitrate fertilisers are used, and the degree of leaching

浸出程度 by rainfall 降雨 .

In the survey of a large body of water such as a lake, the same

spatial 空间的 parameters need to be considered and a similar

pattern of grid and depth sampling employed. Given 给定 the

capacity 容积 of a liquid for ready mixing, it is unlikely in most

cases that samples as closely spaced 紧密间隔 as 10m would be

collected. Depth studies might also be required over rather greater

distances.




Chemistry

It may well be that the dilution effected by the water means that

analytes are present at very low concentrations. The use of

pollution indicators 指标 such as sediments or filter-feeding

shellfish 滤食性贝类 , may be advantageous [ˌædvənˈteɪdʒəs]

有利的 in such circumstances. Seasonal effects here would be

exemplified by seasonal overturn 季节性翻转 , which occurs in

many lakes. In this process thermal effects 热效应 acting on

the water bring about 造成 mixing of the upper and lower

strata twice yearly 每年两次 , in spring and autumn.




Chemistry The sampling of vapours and gaseous [ˈgæsiəs] materials

presents its own special problems. Physically 从体力上看 , the

samples are difficult to handle, and the high mobility of substances

leads to rapid dispersion. Analytes may thus need to be trapped and

concentrated, for example by cooling to 冷却到 a liquid form, or

sorption on to 吸附到 a solid surface.

Maintenance 保持 of the integrity [ɪnˈtegrəti] 完整 of the samples cannot be stressed too strongly, and accordingly 因此，于是 their handling and storage after collection, and prior to

analysis, must be given careful consideration. Losses of the analyte

or contamination can occur by simple mechanical means, 手工方法 evaporation [ɪˌvæpə'reɪʃn], or absorption from external sources.




ChemistryDecomposition is a possibility and is a particular problem with

对于 organic and biological samples. Refrigerated storage 冷藏is one obvious possible solution. The difficulties outlined above

以上概述 are of especial concern where sampling is being carried

out at site remote from full laboratory facilities. Measurement

on-site 现场 with portable field equipment 便携式野外装备

must then be effected 实行 where necessary.

In many cases it will not be appropriate to carry out the analysis

on the whole of the sample that has been removed to the laboratory

and it will need to be subdivided 细分 . Care must be exercised in

this subdivision process to ensure that the portion separated for

analysis is truly representative of the whole.




ChemistryWhere the material is entirely homogeneous [ˌhoʊməˈdʒi:niəs] or is in a homogeneous solution, this clearly presents no

difficulties. Particulate solids with particles of varying sizes and

densities present special problems. The process of coning and

quartering 堆锥四分法 is often used here. In this, the total

sample is poured into a cone-shaped heap 锥形堆 so that the

heavier particles concentrate at the bottom of the cone [koʊn]

and the lighter ones at the top. One quarter of the cone is then

separated by vertical division, and the process repeated until a

portion of appropriate size for analysis is obtained.

This final portion should contain the same ratio of

particle types as in the original.




Chemistry Sample pretreatments constitute the stage in the analytical

process in which the sample is prepared for measurement of the

analyte. There is no general standard procedure and considerable

variations will be encountered. The analytes in water, for

example, may well need to be concentrated prior to

measurements. Simple evaporation [ɪˌvæpə'reɪʃn], solvent

extraction or other chemical separation procedures may be

required. Solid samples will usually need to be solubilised.

Crushing or grinding 破碎或研磨 followed by treatment with

aggressive 侵蚀性的 chemical reagents, including strong acids

or alkalis, are often used for this. Analyte losses must be carefully

guarded against 预防 at this stage, as must contamination.




Chemistry In ideal circumstances direct measurements can be made on

对 analytes without 如果没有 significant 严重的 matrix

effects

基体效应 or interference. Sometimes this is possible, especially

where spectrometric [spektroʊ‘metrɪk] methods 光谱法 are

employed to distinguish the analyte signal from others. Often,

however, this cannot be achieved and separations are needed.




Chemistry1.4.4 Analytical measurements

The making of an analytical measurement is often the

simplest and most straightforward 直截了当 stage in the

overall process. This is especially so in modern laboratories

where instrumental and automated procedures now dominate.

Many of the important measurement techniques are reviewed

in later chapter. It is timely 及时的 to recall 回想 here that

unless the earlier stages in the analytical process have been

properly executed [ˈeksɪkju:t] 实行 , the results obtained will

be meaningless [ˈmi:nɪŋləs] or, perhaps worse, misleading.




Chemistry1.4.5 Method validation and quality assurance

It is axiomatic [,æksɪə‘mætɪk] ( 不言 ) 自明的 that the

experimental results obtained must give a good indication of the

true result 真值 . The calibrations carried out in setting up the

method go part of the way 走了一段路 to ensuring this. Matrix

effects have previously been mentioned and these are difficult to

allow for fully in calibration standards, unless the matrix is very

simple. Analysis of validated standards, often known as standard

reference materials (SRMs), to check the performance of a method

is almost always essential. Standards used should have a

composition, which is closely similar to 十分类似于 the sample,

both in term of 在… 方面 its analyte concentration and matrix.




ChemistryAs a result of extensive previous analysis by a variety of methods,

the analyte content of the standard is known within narrow limits.

Standards used can be ‘in-house’机构内部的 ones, which have

been established within the laboratory and which are valuable for

the routine checking 例行检查 of method performance.

However, reference must also be made to others which are

accepted nationally and internationally. An extensive range of

such standards is available for many different analytes in widely

varying matrices. They can be obtained from bodies 团体 like

the National Institute of Standards and Testing (NIST), in the

United States, the Bureau of Certified Reference Materials (BCR)

in Europe, or the Laboratory of the Government Chemist (LGC)

in the UK.




Chemistry An initial validation 确认，认可 of a procedure is not in

itself sufficient to guarantee the continuing quality of the data

generated over an extended period. 在一段长时间 In order to

do this, an ongoing 不间断的 quality assurance (QA)

programme must be employed. Results obtained in

environmental analysis, frequently have legal [‘ligl] 法律的

as well as scientific implications. Hence the quality of the data

is doubly important 倍加重要 , as it may have to be

defended in a court of law, and match legal standards of proof.

A QA programme must be comprehensive and inclusive 具综合性和包容性 of the whole analytical operation. It has two

main elements.




Chemistry

The first is the development, validation and recording of the

overall procedure and ensuring that as far as possible 尽可能地 samples are all handled in exact compliance with 严格遵守 the defined procedure. This procedure must ensure the

traceability 溯源性 of the processing 处理 of each

individual sample and measurement. The second requires

regular 定期的 performance monitoring. Routine analysis of

reference samples and maintenance 保持 of quality control

charts (section 2.5.5), are important tools in this.




Chemistry1.4.6 Data assessment and interpretation The data yielded by an analytical programme are used to try to fulfil

the original aims defined at the beginning. A two-stage process is

required for this. The reliability of the data must first be assessed. As

discussed in chapter 2, errors are implicit in all measurements and

correct procedures must be used to ensure that data with excessive

errors, which may endanger the validity 有效性 of the conclusions,

are not used. It is then possible to attempt to interpret the data in the

light of 按照 ,根据 the defined aims of the measurement. A blend

of environmental, analytical and statistical expertise [‘ɛkspɝ’tiz] 专门知识 will be required to do this soundly. Careful thought should

also be given to data presentation, so that it is readily digested and

conclusions are clearly demonstrated.




Chemistry1.4.7 Safety

A safety assessment for the programme 计划 and the

activities within it must be routinely made 进行 . It is

important to bear in mind, that the initial interest in

environmental analytes often derivers from their hazardous

properties, and that special precautions 预防措施 may well

be needed when dealing with some analytes. The main

problem will often arise not so much with 由于 the samples

themselves, as with the preparation and handling of standards

which utilize higher concentrations of the analyte.




ChemistryReview

Review



Chemistry


• 1. Write down the stages of overall analytical process

in an environmental investigation. What needs to be

taken into account in each stage?

• 2. How to select an analytical method？




ChemistryReferences• 1. Fifield F.W. and Haines P.J. Environmental

Analytical Chemistry (Second Edition). Blackwell

Science Ltd, 2000.

• 2. 但德忠主编 . 环境分析化学 . 高等教育出版社 , 2009.

• 3. 大连理工大学分析化学教研室主编 . 分析化学 (双语版 )(国家精品课程教材 ). 大连理工大学出版社， 2008.

• 4. 汪尔康主编 . 21世纪的分析化学（中国科学院研究生教学丛书） . 科学出版社 , 2001.

References



Chemistry

Thank you!

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Chapter 1 Introduction Environmental Analytical Chemistry Environmental Analytical Chemistry Chapter 1 Introduction 精品课程