INTRODUCTION TO
INSTRUMENTAL ANALYSIS
SPT2203
INTRODUCTION
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INSTRUMENTAL ANALYSIS IS A COMPONENT OF ANALYTICAL
CHEMISTRY THAT USES INSTRUMENTS TO ANALYSE PARTICLES
AND MOLECULES
CLASSIFICATION OF
ANALYTICAL METHODS
Qualitative vs Quantitative
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Qualitative instrumental analysis is that measured property that indicates presence of analyte in matrix
Quantitative instrumental analysis is that magnitude of measured property that is proportional to concentration of
analyte in matrix
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Species of interest : All constituents including analyte.
Often need pretreatment - chemical extraction, distillation, separation, precipitation
SOURCES OF ERROR
• Incorrect weighing and transfer of analytes and standards
• Inefficient extraction of the analyte from a matrix
• Incorrect use of pipettes, burettes or volumetric flasks for
volume measurement
• Failure to use a blank
SELECTING AN
ANALYTICAL METHOD
• How reproducible – precision
• How close to true value – accuracy/bias
• How small a difference can be measured – sensitivity
• What range of amounts – dynamic range
• How much interference – selectivity
• How many samples - efficience
PRECISION
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THE PRECISION OF AN ANALYTICAL
PROCEDURE EXPRESSES THE CLOSENESS
OF AGREEMENT (DEGREE OF SCATTER)
BETWEEN A SERIES OF MEASUREMENTS
OBTAINED FROM MULTIPLE SAMPLING OF
THE SAME HOMOGENEOUS SAMPLE UNDER
THE PRESCRIBED CONDITIONS.
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PRECISION MAY BE CONSIDERED AT THREE
LEVELS: REPEATABILITY, INTERMEDIATE
PRECISION AND REPRODUCIBILITY.
T H E A C C U R A C Y O F A N A N A LY T I C A L P R O C E D U R E E X P R E S S E S T H E C L O S E N E S S O F A G R E E M E N T
BETWEEN THE VALUE WHICH IS ACCEPTED EITHER AS A CONVENTIONAL TRU E VALUE OR AN
ACCEPTED REFERENCE VALUE AND THE VALUE FOUND. THIS IS SOMETIMES TERMED TRUENESS.
S P E C I F I C I T Y I S T H E A B I L I T Y T O A S S E S S U N E Q U I V O C A L LY T H E A N A LY T E I N T H E P R E S E N C E O F
C O M P O N E N T S W H I C H M AY B E E X P E C T E D T O B E P R E S E N T. T Y P I C A L LY T H E S E M I G H T I N C L U D E
I M P U R I T I E S , D E G R A D A N T S , M AT R I X
N O A N A LY T I C A L M E T H O D I S C O M P L E T E LY F R E E F R O M I N T E R F E R E N C E BY C O N C O M I TA N T S . B E S T
M E T H O D I S M O R E S E N S I T I V E T O A N A LY T E T H A N I N T E R F E R I N G S P E C I E S ( I N T E R F E R E N T ) . T H E
S E N S I T I V I T Y O F M E T H O D I N D I C AT E S H O W R E S P O N S I V E I T I S T O A S M A L L C H A N G E I N T H E
C O N C E N T R AT I O N O F A N A N A LY T E .
L I N E A R I T Y T H E L I N E A R I T Y O F A N A N A LY T I C A L P R O C E D U R E I S I T S A B I L I T Y ( W I T H I N A G I V E N
R A N G E ) T O O B TA I N T E S T R E S U LT S W H I C H A R E D I R E C T LY P R O P O R T I O N A L T O T H E
C O N C E N T R AT I O N ( A M O U N T ) O F A N A LY T E I N T H E S A M P L E .
SAMPLE WHICH CAN BE QUANTITATIVELY DETERMINED WITH SUITABLE
PRECISION AND ACCURACY. THE QUANTITATION LIMIT IS A PARAMETER OF
QUANTITATIVE ASSAYS FOR LOW LEVELS OF COMPOUNDS IN SAMPLE
MATRICES, AND IS USED PARTICULARLY FOR THE DETERMINATION OF
IMPURITIES AND/OR DEGRADATION PRODUCTS.
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ROBUSTNESS THE ROBUSTNESS OF AN ANALYTICAL PROCEDURE IS A
MEASURE OF ITS CAPACITY TO REMAIN UNAFFECTED BY SMALL, BUT
DELIBERATE VARIATIONS IN METHOD PARAMETERS AND PROVIDES AN
INDICATION OF ITS RELIABILITY DURING NORMAL USAGE. ROBUSTNESS.
THE TYPES OF PARAMETERS WHICH ARE ASSESSED IN ORDER TO
DETERMINE THE ROBUSTNESS OF A METHOD INCLUDE: THE STABILITY OF
ANALYTICAL SOLUTIONS; THE LENGTH OF THE EXTRACTION TIME; THE
EFFECT OF VARIATIONS IN THE PH OF A HPLC MOBILE PHASE; THE EFFECT
OF SMALL VARIATIONS IN MOBILE PHASE COMPOSITION; THE EFFECT OF
CHANGING CHROMATOGRAPHIC COLUMNS; THE EFFECT OF
TEMPERATURE AND FLOW RATE DURING CHROMATOGRAPHY.
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RANGE THE RANGE OF AN ANALYTICAL PROCEDURE IS THE INTERVAL
BETWEEN THE UPPER AND LOWER CONCENTRATION (AMOUNTS) OF
ANALYTE IN THE SAMPLE (INCLUDING THESE CONCENTRATIONS) FOR
WHICH IT HAS BEEN DEMONSTRATED THAT THE ANALYTICAL PROCEDURE
HAS A SUITABLE LEVEL OF PRECISION, ACCURACY AND LINEARITY. WHEN
APPLIED TO THE PERFORMANCE OF AN ASSAY, IT REFERS TO THE
INTERVAL BETWEEN THE UPPER AND LOWER CONCENTRATION OF AN
ANALYTE FOR WHICH AN ACCEPTABLE LEVEL OF PRECISION AND
ACCURACY HAS BEEN ESTABLISHED.
ERROR MINIMIZATION
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Analyst has no control on random
errors but systemic errors can be
reduced by following methods.
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Calibration of apparatus: By
calibrating all the instruments,
errors can be minimized and
appropriate corrections are
applied to the original
measurements.
Control determination: standard
substance is used in experiment in
identical experimental condition to
minimize the errors.
Blank determination: By omitting
sample, a determination is carried out
in identical condition to minimize the
errors occurs due to impurities present
in reagent.
ERROR
MINIMIZATION….
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Parallel determination: Instead of single
determination, duplicate or triplicate
determination is carried out to minimize
the possibilities of accidental errors.
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Standard edition: This method is generally applied to physico-chemical procedures such as
polarography and spectrophotometry.
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Internal standards: It is used in spectroscopic and chromatographic determination.
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Independent method of analysis: It is carried out to maintain accuracy of the result e. g. Iron
(III) is first determined gravimetrically by precipitation method as iron (III) hydroxide and then
determined titrimetrically by reduction to the iron (II) state.
ERROR ANALYSIS CASE STUDY
o A batch of paracetamol tablets are stated to
contain 500 mg of paracetamol per tablet; for
the purpose of this example it is presumed that
100% of the stated content is the correct
answer. Four students carry out a
spectrophotometric analysis of an extract from
the tablets and obtain the following
percentages of stated content for the repeat
analysis of paracetamol in the tablets:
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Student 1: 99.5%, 99.9%, 100.2%, 99.4%, 100.5%
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Student 2: 95.6%, 96.1%, 95.2%, 95.1%, 96.1%
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Student 3: 93.5%, 98.3%, 92.5%, 102.5%, 97.6%
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Student 4: 94.4%, 100.2%, 104.5%, 97.4%,
102.1%
ANY QUESTIONS?
THANK YOU
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