Analytical Design

CH217

CH217Fundamentals of Analytical Chemistry Module Leader: Dr. Alison Willows

Created with MindGenius Business 20051

Created with MindGenius Business 2005Assessment Practicals 60%Practical 1: online quiz during lab sessionPracticals 2 & 3: electronic reports, see lab scriptsEnd of module examination 40%In addition you are also required to:Complete the guided study (not assessed)Attend all the labsAttend at least 80% lectures/workshops


StudentcentralModule content and assignments are available through studentcentralYou will be required to submit your coursework electronically via studentcentralThe guided study will be an electronic test on studentcentralFeedback on assessments will also be electronic

Please familiarise yourself with studentcentral!

Created with MindGenius Business 2005Recommended readingThe module descriptor tells you what you should know by the end of this moduleThe information given in lectures and on studentcentral is only a guideline to aid your studyPlease refer to the module learning handbook and studentcentral for a list of recommended books and other useful resources.You will not achieve a good grade in this module without doing additional reading outside of the lectures

Created with MindGenius Business 2005 Principles of Analytical design DTI's Valid Analytical Measurement programme

The six principles of good analytical practiceAnalytical measurements should be made to satisfy an agreed requirement.Analytical measurements should be made using methods and equipment which have been tested to ensure they are fit for purpose.Staff making analytical measurements should be both qualified and competent to undertake the task.There should be a regular independent assessment of the technical performance of a laboratoryAnalytical measurements made in one location should be consistent with those elsewhere.Organisations making analytical measurements should have well defined quality control and quality assurance procedures.Created with MindGenius Business 2005 Principles of Analytical design

DTI's Valid Analytical Measurement programme

The six principles of good analytical practiceAnalytical measurements should be made to satisfy an agreed requirement.Analytical measurements should be made using methods and equipment which have been tested to ensure they are fit for purpose.Staff making analytical measurements should be both qualified and competent to undertake the task.There should be a regular independent assessment of the technical performance of a laboratoryAnalytical measurements made in one location should be consistent with those elsewhere.Organisations making analytical measurements should have well defined quality control and quality assurance procedures.

role of analytical chemistry in science

Do I need analytical chemistry?Analytical chemistry mightenable you to pass your coursehelp you to understand other modulesbe useful in your careerbe interestinghelp with your final year projectchange your life!

What is analytical chemistry?Dictionary definitionsAnalytical (adj) examining or tending to examine things very carefullyChemistry(noun) 1.(the part of science which studies) the basic characteristics of substances and the different ways in which they react or combine with other substances. 2. INFORMAL understanding and attraction between two peopleCambridge Advanced Learner's dictionary

Analytical chemistry encompasses any type of test that provides information on the amount or identification of the chemical composition of a sample.

This breaks down into two main areas of analysis: qualitative and quantitative

Qualitative analyses give a positive/negative or yes/no answer. This tells us whether a substance (the analyte) is present but doesn't tell us how much is there. One example is a home pregnancy test which indicates the presence (positive) or lack (negative) of a pregnancy by analysing a hormone that appears in a woman's blood and urine, human chorionic gonadotropin (HCG). In this case we do not need to know how much of the hormone is present so a qualitative analysis is sufficient. A qualitative analysis may also identify substances in a sample

Quantitative analyses tell us how much of a substance is in the sample. One example is a diabetes glucose monitor that measures the amount of glucose in the blood

When and where is analytical chemistry used?

Food industry - wine production; contaminants; process linesMedical - blood analysis; imaging; pharmaceutical - drug analysisenvironmental - water, gas & soil analysisengineering - materials characterisationcrime - forensics (CSI)sport & leisure - pool chlorination; drugs testsResearch

Calibration

Analytical methods, particularly those using instruments, frequently require calibration procedures

These are to establish:the response to known quantities of analyte (standards) within the range usedthe reliability/drift of the methodlimits beyond which detection/quantitation is unreliable

Calibration normally involves:measurement of samples of known concentrationsmeasurement of a relevant range of concentrationsa range in which the response is lineargraphical treatment of resultsmodified calculation of errors

reporting

Analytical DocumentationWritten analytical procedures are used to allow other competent analysts to reproduce the method. Sufficient detail is required to obtain consistent results. Trained and competent personnel are still required even when a full detailed document is availableAnalytical Documentation for ProceduresScope and applicabilitySamplesAnalytesRangesDescription and principle of the methodEquipmentSpecificationCalibration and qualificationRange of operabilityReference materials and reagentsSpecificationPreparationStorageHealth & SafetySamplingMethodsStorageLimitationsAnalytical ProcedurePreparation of samplesPreparation of standardsCritical factorsDetailed description of all stepsTypical outputs; chromatograms, spectra, etc.Recording and reporting of dataMethodRounding and significant figuresData treatmentsCalculation of resultsCalibration modelCalculation methodsAssumptions and limitationsMethod performanceStatistical measuresControl chartingReferences & Bibliography

Drawing conclusionsIn a written report of an experiment you must come to some conclusion about the workUse the information from the statistical tests and performance parameters Pull together all the informationKeep the wording analytical i.e. use accurate and precise correctly, and dont over-generaliseMake informed judgements about the technique and compare to other possible techniques

6 Role of analytical chemistry in science Do I need analytical chemistry?Analytical chemistry might:enable you to pass your coursehelp you to understand other modulesbe useful in your careerbe interestinghelp with your final year projectchange your life!

Created with MindGenius Business 2005 role of analytical chemistry in science

Do I need analytical chemistry?Analytical chemistry mightenable you to pass your coursehelp you to understand other modulesbe useful in your careerbe interestinghelp with your final year projectchange your life!

What is analytical chemistry?Dictionary definitionsAnalytical (adj) examining or tending to examine things very carefullyChemistry(noun) 1.(the part of science which studies) the basic characteristics of substances and the different ways in which they react or combine with other substances. 2. INFORMAL understanding and attraction between two peopleCambridge Advanced Learner's dictionary

Analytical chemistry encompasses any type of test that provides information on the amount or identification of the chemical composition of a sample.

This breaks down into two main areas of analysis: qualitative and quantitative

Qualitative analyses give a positive/negative or yes/no answer. This tells us whether a substance (the analyte) is present but doesn't tell us how much is there. One example is a home pregnancy test which indicates the presence (positive) or lack (negative) of a pregnancy by analysing a hormone that appears in a woman's blood and urine, human chorionic gonadotropin (HCG). In this case we do not need to know how much of the hormone is present so a qualitative analysis is sufficient. A qualitative analysis may also identify substances in a sample

Quantitative analyses tell us how much of a substance is in the sample. One example is a diabetes glucose monitor that measures the amount of glucose in the blood


Food industry - wine production; contaminants; process linesMedical - blood analysis; imaging; pharmaceutical - drug analysisenvironmental - water, gas & soil analysisengineering - materials characterisationcrime - forensics (CSI)sport & leisure - pool chlorination; drugs testsResearch

Analytical Process

The analytical process

Formulating the questionSelecting analytical proceduresconducting the analysisSampling Sample preparationcalibration of methodSample analysiscollection and processing of data and calculation of errorsmethod validationReporting and interpretation (Results & discussion)Drawing conclusions (answering the question!)

7

What is analytical chemistry?

Dictionary definitionsAnalytical (adj) examining or tending to examine things very carefullyChemistry(noun) 1.(the part of science which studies) the basic characteristics of substances and the different ways in which they react or combine with other substances. 2. INFORMAL understanding and attraction between two peopleCambridge Advanced Learner's dictionaryAnalytical chemistry encompasses any type of test that provides information on the amount or identification of the chemical composition of a sample.This breaks down into two mainareas of analysis: qualitative and quantitativeCreated with MindGenius Business 2005Qualitative vs.. QuantitativeQualitative analyses give a positive/negative or yes/no answer. This tells us whether a substance (the analyte) is present but doesn't tell us how much is there. A qualitative analysis may also identify substances in a sample

Quantitative analyses tell us how much of a substance is in the sample.



Food industry - wine production; contaminants; process linesMedical - blood analysis; imaging; Pharmaceutical - drug analysisEnvironmental - water, gas & soil analysisEngineering - materials characterisationCrime - forensics (CSI)Sport & leisure - pool chlorination; drugs testsResearch

Created with MindGenius Business 2005 Analytical Process Formulating the questionSelecting analytical proceduresConducting the analysisSampling Sample preparationcalibration of methodSample analysisCollection and processing of data and calculation of errors

Created with MindGenius Business 2005 Analytical Process

The analytical process

Formulating the questionSelecting analytical proceduresconducting the analysisSampling Sample preparationcalibration of methodSample analysiscollection and processing of data and calculation of errorsmethod validationReporting and interpretation (Results & discussion)Drawing conclusions (answering the question!)

11Analytical Process, cont.Method validationReporting and interpretation (results & discussion)Drawing conclusions (answering the question!)Created with MindGenius Business 2005 Method selection Valid Analytical Measurement (VAM) A result is fit for purpose when its uncertainty maximises its expected utility (cost, usually)reducing uncertainty generally increases the cost of analysismost users have tight budgetsuncertainty in measurement should be as large as can be tolerated to keep costs downother factors can affect fitness for purposesensitivity of techniquesample throughputaccuracy and precision that is obtainablesample type and preparation

Created with MindGenius Business 2005 Valid Analytical Measurement (VAM)

A result is fit for purpose when its uncertainty maximises its expected utility (cost, usually)

reducing uncertainty generally increases the cost of analysismost users have tight budgetsuncertainty in measurement should be as large as can be tolerated to keep costs downother factors can affect fitness for purposesensitivity of techniquesample throughputaccuracy and precision that is obtainablesample type and preparation

Ultimately, the results are fit for purpose if they meet the specific needs of the customer, the customer is confident in the results and they represent value for money.

comparing techniques statistically

Student's t test

A t test can be used to decide if two sets of results are "the same" or to compare a set of results with a known value.

You will have learnt the t test in your QS modules, please refresh your memory if you are unsure how to perform it.

Worked examples

Practice questions

F test

Is there a significant difference between the precision of two methods? i.e. are the standard deviations of the two methods significantly different?

Worked Examples

Practice questions

Categories: know basics

13VAM, contUltimately, the results are fit for purpose if they meet the specific needs of the customer, the customer is confident in the results and they represent value for money.

Created with MindGenius Business 2005 Valid Analytical Measurement (VAM) Goldmine A sampling and analysis game for Minitab can be found here

http://www.rsc.org/Membership/Networking/InterestGroups/Analytical/AMC/Software/goldmine.asp

Created with MindGenius Business 2005 Valid Analytical Measurement (VAM)

A result is fit for purpose when its uncertainty maximises its expected utility (cost, usually)

reducing uncertainty generally increases the cost of analysismost users have tight budgetsuncertainty in measurement should be as large as can be tolerated to keep costs downother factors can affect fitness for purposesensitivity of techniquesample throughputaccuracy and precision that is obtainablesample type and preparation

Ultimately, the results are fit for purpose if they meet the specific needs of the customer, the customer is confident in the results and they represent value for money.

Goldmine

A sampling and analysis game for Minitab can be found at http://www.rsc.org/Membership/Networking/InterestGroups/Analytical/AMC/Software/goldmine.asphttp://www.rsc.org/Membership/Networking/InterestGroups/Analytical/AMC/Software/goldmine.asp

15 Comparing techniques statistically The F test and Student's t test

F test -Is there a significant difference between the precision of two methods? i.e. are the standard deviations of the two methods significantly different?Students t test - used to decide if two sets of results are "the same" or to compare a set of results with a known value.

You will have learnt these tests in your QS modules, please refresh your memory if you are unsure how to perform it.You will be expected to be able to compare a set of results with a known value, compare two sets of matched results and compare two sets of unmatched results, please see me if you can not do thisFurther information and worked examples are available on the CH217 studentcentral website

Created with MindGenius Business 2005 comparing techniques statistically

Student's t test

A t test can be used to decide if two sets of results are "the same" or to compare a set of results with a known value.

You will have learnt the t test in your QS modules, please refresh your memory if you are unsure how to perform it.

Worked examples

Practice questions

F test

Is there a significant difference between the precision of two methods? i.e. are the standard deviations of the two methods significantly different?

Worked Examples

Practice questions


16 Samples - sampling strategy Probably the most important stage in any analysis.

If the sample taken is not representative of the original material everything you do next is worthless.

Created with MindGenius Business 2005 sampling strategy

Probably the most important stage in any analysis.

If the sample taken is not representative of the original material everything you do next is worthless.

Sample nomenclature:lot - quantity of material which is assumed to represent a single population for sampling purposesbatch - quantity of material known (or assumed) to have been produced under uniform conditionsincrements - portions of material obtained using a sampling device from lot/batchprimary/gross sample - combination of incrementscomposite/aggregate sample - combination of primary sampleslaboratory sample - portion of material delivered to lab for analysistest (analytical) portion - material actually submitted for analysis

Horowitz. Pure and Applied Chemistry, 1990, 62, 1193-1208.

Obtaining a representative sample:Usually the lot is not homogeneous but may be randomly heterogeneous (different compositions occur on a small scale and randomly) or segregated heterogeneous (large patches of different compositions)

A representative sample will not reflect the composition of the target exactly but will be adequate enough to be 'fit for purpose'.There will always be a degree of uncertainty from sampling.

n numbers

How many replicate samples do we need to analyse?Often in biology you will come across n=6 for all analyses. so where does this come from?

Confidence limits - met in QS modules

Rearrange to make n the subject

Use the acceptable error and confidence level to calculate n.

Worked example

17Sample nomenclature

lot - quantity of material which is assumed to represent a single population for sampling purposesbatch - quantity of material known (or assumed) to have been produced under uniform conditionsincrements - portions of material obtained using a sampling device from lot/batchprimary/gross sample - combination of incrementscomposite/aggregate sample - combination of primary sampleslaboratory sample - portion of material delivered to lab for analysistest (analytical) portion - material actually submitted for analysisCreated with MindGenius Business 2005Sampling - stages

Horwitz. Pure and Applied Chemistry, 1990, 62, 1193-1208.Created with MindGenius Business 2005Obtaining a representative sample

Usually the lot is not homogeneous but may be randomly heterogeneous (different compositions occur on a small scale and randomly) or segregated heterogeneous (large patches of different compositions)

A representative sample will not reflect the composition of the target exactly but will be adequate enough to be 'fit for purpose'. There will always be a degree of uncertainty from sampling.Created with MindGenius Business 2005Sampling - n numbers How many replicate samples do we need to analyse?Often in biology you will come across n=6 for all analyses. so where does this come from?



Use the acceptable error and confidence level (to find t) to calculate n.

Created with MindGenius Business 2005 n numbers

How many replicate samples do we need to analyse?Often in biology you will come across n=6 for all analyses. so where does this come from?



Use the acceptable error and confidence level to calculate n.

Worked example

21Sampling - n numbers Worked ExampleThe concentration of lead in the bloodstream was measured for a sample of children from a large school near a busy main road. A preliminary sampling of 50 children gave a mean concentration of 10.12 ng ml-1 and standard deviation of 0.64 ng ml-1. How big does the sample need to be to give an error of less than 0.1 ng ml-1 with 95% confidence? For 95% confidence t = 1.96 (n = )

So 160 children would need to be tested

Created with MindGenius Business 2005 sample preparation Preparing samples for analysisDepends on the form required for analysisSamples may require

Moisture controlGrindingDissolvingAshingFusionExtractionPreconcentration/dilutionDerivatisationor a combination of several of theseInstruments such as microwave ovens, sonicating baths, pressure vessels (digestion bombs) and extraction cartridges may also be used.Please see recommended reading for further details on these preparation techniques (ch28 Harris)

Created with MindGenius Business 2005 sample preparation

Preparing samples for analysis

Depends on the form required for analysis

Samples may require1) Moisture control2) Grinding3) Dissolving4) Ashing5) Fusion6) Extraction7) Preconcentration/dilution8) Derivatisation or a combination of several of these

Instruments such as microwave ovens, sonicating baths, pressure vessels (digestion bombs) and extraction cartridges may also be used.

Please see recommended reading for further details on these preparation techniques (ch28 Harris)

Remember: The success of the analysis depends on minimising errors throughout all stages including sample preparation Every additional step must be carefully controlled and included in error calculations The greater the n the more confident we can be

solid phase extraction

Analyte is removed from sample by passing a solution over a solid. Analyte is adsorbed, or absorbed by the solid and the remaining liquid can be discarded Analyte is eluted by use of a stronger solvent

(Harris ch28) SPE uses the principles of chromatographic separation - works on ion exchange, reverse phase and normal phaseSPE can reduce solvent consumption SPE is now often used as an efficient alternative to liquid extraction - depends on availability of selective adsorbentscartridges are available commercially for many analysesoften used to change the buffer or matrix that the analyte is held in

23 solid phase extraction Analyte is removed from sample by passing a solution over a solid. Analyte is adsorbed, or absorbed by the solid and the remaining liquid can be discarded Analyte is eluted by use of a stronger solvent

Created with MindGenius Business 2005 solid phase extraction

Analyte is removed from sample by passing a solution over a solid. Analyte is adsorbed, or absorbed by the solid and the remaining liquid can be discarded Analyte is eluted by use of a stronger solvent

(Harris ch28) SPE uses the principles of chromatographic separation - works on ion exchange, reverse phase and normal phaseSPE can reduce solvent consumption SPE is now often used as an efficient alternative to liquid extraction - depends on availability of selective adsorbentscartridges are available commercially for many analysesoften used to change the buffer or matrix that the analyte is held in

24 solid phase extraction

Created with MindGenius Business 2005 Sample storage To keep samples reflective we must prevent contamination & decompositionProblems & SolutionsDirty containers - ensure adequate washing; use disposable containersType of Container - Avoid ion-exchange and adsorption of analyteLight - use brown/foil-covered bottlesAir may oxidise sample - store under vacuum, or in a protective atmosphereMoisture - keep tightly sealedEvaporation - keep tightly sealedHeat/cold - store in fridge/temperature controlled room

The measures chosen will depend on the analyte and its sample matrixCreated with MindGenius Business 2005 storage

Storing Samples

To keep samples reflective we must prevent contamination decomposition

Problems & Solutions1) Dirty containers - ensure adequate washing; use disposable containers2) Type of Container - Avoid ion-exchange and adsorption of analyte3) Light - use brown/foil-covered bottles4) Air may oxidise sample - store under vacuum, or in a protective atmosphere5) Moisture - keep tightly sealed6) Evaporation- keep tightly sealed7) Heat/cold - store in fridge/temperature controlled room

The measures chosen will depend on the analyte and its sample matrix

26 Calibration Analytical methods, particularly those using instruments, frequently require calibration procedures



Created with MindGenius Business 2005 Calibration

Analytical methods, particularly those using instruments, frequently require calibration procedures



External Standard

Simplest and most common form of calibration. Prepare samples containing known quantities of analyte over a relevant range including blanksControls for sample preparation/matrix should be used, matched to the unknown samples Carry out and record measurements Plot quantity/concentration of analyte vs. response Linear regression with least squares analysis is used to determine response (expressed as y = bx+a) Repeat as and when appropriate (when it is likely that an unacceptable drift will have occurred)

Advantages May only need one calibration plot (of 5-10 samples) for 10s to 100s of unknown samples Can be easily automated Simple statistics will provide estimates of uncertainty for the method

Disadvantages Requires care to match conditions and matrix to that of the unknown samples Does not control for sudden changes in method performance

You will have done this in more detail in BY131 You should be able to use linear regression to calculate the line of best fit and calulate the errors in the calibration line to calculate the concentration of the analyte and its error from this information (see sec 5.4, 5.5, 5.6 in Miller & Miller).The ability to do this is assumed in this module.


Internal Standard

Useful for methods which are not very reproducible; e.g. Gas chromatography uses very small volumes (

Documents

Analytical Design