Quality assurance and quality control programs are necessary to ensure the validity and reliability of analytical environmental data. Several studies have shown large variations in results for identical samples analyzed by different laboratories. AQC programs establish procedures for sample collection, analysis, calibration, quality control checks, and data reporting. Key aspects include standard methods, analyst training, instrument maintenance, calibration verification, internal quality control samples, and inter-laboratory sample exchanges to check for accuracy. Control charts can be used to monitor results and identify any loss of statistical control that could indicate errors have been introduced. Both precision and accuracy are important to consider when evaluating results.
QC Multi-rules are designed and used to minimise false rejections and maintain a high rate of error detection. There are six main rules used to determine if results from a run of patient samples should be accepted or rejected, based on the performance of control materials against the rule criteria. Different combinations can be applied depending on the number of controls in use, total allowable error and the instrument in use. The flow chart below is often used to determine if a run should be accepted or rejected.
Basic QC Statistics - Improving Laboratory Performance Through Quality Contro...Randox
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QC Multi-rules are designed and used to minimise false rejections and maintain a high rate of error detection. There are six main rules used to determine if results from a run of patient samples should be accepted or rejected, based on the performance of control materials against the rule criteria. Different combinations can be applied depending on the number of controls in use, total allowable error and the instrument in use. The flow chart below is often used to determine if a run should be accepted or rejected.
Basic QC Statistics - Improving Laboratory Performance Through Quality Contro...Randox
Randox Quality Control's latest educational guide examines Internal Quality Control, External Quality Assessment, Why laboratories should run QC, How often laboratories should run QC, Basic QC statistics and the quality control process.
How to establish QC reference ranges - Randox QC Educational GuideRandox
Establishing QC reference ranges is an important aspect of laboratory quality. Find out how to effectively set reference ranges with our educational guide.
Harmonization of Laboratory Indicators, 09 03-2017Ola Elgaddar
Most of Medical labs are having KPIs to monitor their performance and enhance process improvement. This presentation discusses in short the IFCC attempts to reach a consensus and harmonize medical labs quality indicators.
Designing an appropriate QC procedure for your laboratoryRandox
Improving Laboratory Performance Through Quality Control - Five Simple Steps for QC Success.
It is easy to get caught up in an abundance of QC statistics and forget the fundamental reason why
QC exists in the first instance. QC is about detecting errors and ensuring that the results you
produce are accurate and reliable. All QC procedures should focus on reducing the risk of harm
to the patient. We are not examining statistics; we are examining real patients, real results and real
lives. Around 70% of all medical decisions are based on laboratory results, which is why it is of
utmost importance that each and every laboratory, has a well-designed QC procedure in place.
Improving Laboratory Performance Through Quality Control - The role of EQA in...Randox
Randox Quality Control's five simple steps to QC success. The second education guide from Randox QC for clinical laboratory staff. The guide will examine how EQA works, benefits of EQA and what a laboratory should look for when choosing an EQA scheme.
QUALITY
Conformance to the requirements of users or customers satisfaction of their needs and expectations.
Total Quality Management
A management approach that focuses on processes and their improvement.
Monitoring External Quality Assessment / Proficiency Testing Performance - Investigating the source of the problem.
In order to identify the source of the problem it is useful to be aware of the most common causes of poor EQA performance. Errors can occur at any
stage of the testing process however EQA is most concerned with detecting analytical errors i.e. errors that occur during the analysis of the sample.
Most analytical errors can be easily divided into three main areas; clerical errors, systematic errors and random errors. Systematic errors result in
inaccurate results that consistently show a positive or negative bias. Random errors on the other hand affect precision and result in fluctuations in
either direction.
In the continuous quality journey, Controlling laboratory Errors is an integral part & focusing on analytical, post-analytical process is the first step. Developing a reporting culture followed by thorough analysis and implementation of appropriate corrective, preventive actions is required.
How often is Right for Laboratory Quality Control?Randox
Improving Laboratory Performance Through QC - How often is right for QC? Ask the Right Questions to get the Right Answers.
It is widely accepted that laboratories should perform QC at least every day of patient testing. However, is this adequate for every assay and for every laboratory? Is running QC once per day really sufficient? what is the "right" frequency for running QC samples in your laboratory?
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Step by step guide for clinical laboratories wishing to troubleshoot poor QC or EQA performance. Tips on how to distinguish between random error and systematic error. Suggested corrective actions are also provided.
Laboratory Management With Constrains Iamm 2010PathKind Labs
Clinical laboratory services are a critical yet much neglected component of health systems in resource poor countries. They are crucial for public health, disease control and surveillance, and guide patient diagnosis and care, but their key role is often not recognized by governments or donors. Laboratory tests should be used to improve the outcome for individual patients or to provide public health information. However, if the quality of laboratory tests is poor, resources will be wasted on repeat tests or inappropriate management and the laboratory service will be inefficient.
The primary goal of Laboratory Medicine is to provide information that is useful to assist medical decision-making, allowing optimal health care. This can only be obtained by generating reliable analytical results on patient samples. Meaningful measurements are indeed essential for the diagnosis, monitoring, treatment, and risk assessment of patients. Inadequate laboratory performance may have extensive consequences for practical medicine, healthcare system, and, in conclusion, for the patient. Poor quality results may actually lead to incorrect interpretation by the clinician, impairing the patient’s
situation.
Accreditation authorities have identified twelve quality system essentials that need to be in place for a laboratory to perform clinical tests adequately and in a quality assured manner. Along with each laboratory performing tests that are in its scope, it is essential that duplication and excess capacity is addressed by forging and operating a network of laboratories leading to consolidation and integration of clinical testing. A network would have collection centers at places convenient to the patients, supported by frequent transfer of samples in appropriate conditions to the laboratory. In the laboratory there is a need for increased automation and relevant training of personnel and the setting up of centralized accessioning, pneumontic chutes for transport of samples to the work bench and for bidirectional interphased equipment to transfer results to desk top of laboratory physicians and after validation of results for the results to be electronically transferred by SMS and/or PDF files via email and/or becoming available online for clients, supplemented by delivery of hard copies of the results.
The challenge in the next decade for laboratory medicine is to accomplish these major changes in organization to meet fiscal restraint and shortage of adequately trained laboratory personnel. Collaborative networks, constructive use of point of care devices, and the development of rapport between laboratories and their clients leading to cost effective utilization of limited resources, are some of the strategies that will maximize patient benefit
Quality control (QC) is a procedure or set of procedures intended to ensure that a manufactured product or performed service adheres to a defined set of quality criteria or meets the requirements of the client or customer. QC is similar to, but not identical with, quality assurance (QA).
QC IN clinical biochemistry labs and hospitals
Harmonization of Laboratory Indicators, 09 03-2017Ola Elgaddar
Most of Medical labs are having KPIs to monitor their performance and enhance process improvement. This presentation discusses in short the IFCC attempts to reach a consensus and harmonize medical labs quality indicators.
Designing an appropriate QC procedure for your laboratoryRandox
Improving Laboratory Performance Through Quality Control - Five Simple Steps for QC Success.
It is easy to get caught up in an abundance of QC statistics and forget the fundamental reason why
QC exists in the first instance. QC is about detecting errors and ensuring that the results you
produce are accurate and reliable. All QC procedures should focus on reducing the risk of harm
to the patient. We are not examining statistics; we are examining real patients, real results and real
lives. Around 70% of all medical decisions are based on laboratory results, which is why it is of
utmost importance that each and every laboratory, has a well-designed QC procedure in place.
Improving Laboratory Performance Through Quality Control - The role of EQA in...Randox
Randox Quality Control's five simple steps to QC success. The second education guide from Randox QC for clinical laboratory staff. The guide will examine how EQA works, benefits of EQA and what a laboratory should look for when choosing an EQA scheme.
QUALITY
Conformance to the requirements of users or customers satisfaction of their needs and expectations.
Total Quality Management
A management approach that focuses on processes and their improvement.
Monitoring External Quality Assessment / Proficiency Testing Performance - Investigating the source of the problem.
In order to identify the source of the problem it is useful to be aware of the most common causes of poor EQA performance. Errors can occur at any
stage of the testing process however EQA is most concerned with detecting analytical errors i.e. errors that occur during the analysis of the sample.
Most analytical errors can be easily divided into three main areas; clerical errors, systematic errors and random errors. Systematic errors result in
inaccurate results that consistently show a positive or negative bias. Random errors on the other hand affect precision and result in fluctuations in
either direction.
In the continuous quality journey, Controlling laboratory Errors is an integral part & focusing on analytical, post-analytical process is the first step. Developing a reporting culture followed by thorough analysis and implementation of appropriate corrective, preventive actions is required.
How often is Right for Laboratory Quality Control?Randox
Improving Laboratory Performance Through QC - How often is right for QC? Ask the Right Questions to get the Right Answers.
It is widely accepted that laboratories should perform QC at least every day of patient testing. However, is this adequate for every assay and for every laboratory? Is running QC once per day really sufficient? what is the "right" frequency for running QC samples in your laboratory?
Troubleshooting Poor EQA/QC Performance in the Laboratory Randox
Step by step guide for clinical laboratories wishing to troubleshoot poor QC or EQA performance. Tips on how to distinguish between random error and systematic error. Suggested corrective actions are also provided.
Laboratory Management With Constrains Iamm 2010PathKind Labs
Clinical laboratory services are a critical yet much neglected component of health systems in resource poor countries. They are crucial for public health, disease control and surveillance, and guide patient diagnosis and care, but their key role is often not recognized by governments or donors. Laboratory tests should be used to improve the outcome for individual patients or to provide public health information. However, if the quality of laboratory tests is poor, resources will be wasted on repeat tests or inappropriate management and the laboratory service will be inefficient.
The primary goal of Laboratory Medicine is to provide information that is useful to assist medical decision-making, allowing optimal health care. This can only be obtained by generating reliable analytical results on patient samples. Meaningful measurements are indeed essential for the diagnosis, monitoring, treatment, and risk assessment of patients. Inadequate laboratory performance may have extensive consequences for practical medicine, healthcare system, and, in conclusion, for the patient. Poor quality results may actually lead to incorrect interpretation by the clinician, impairing the patient’s
situation.
Accreditation authorities have identified twelve quality system essentials that need to be in place for a laboratory to perform clinical tests adequately and in a quality assured manner. Along with each laboratory performing tests that are in its scope, it is essential that duplication and excess capacity is addressed by forging and operating a network of laboratories leading to consolidation and integration of clinical testing. A network would have collection centers at places convenient to the patients, supported by frequent transfer of samples in appropriate conditions to the laboratory. In the laboratory there is a need for increased automation and relevant training of personnel and the setting up of centralized accessioning, pneumontic chutes for transport of samples to the work bench and for bidirectional interphased equipment to transfer results to desk top of laboratory physicians and after validation of results for the results to be electronically transferred by SMS and/or PDF files via email and/or becoming available online for clients, supplemented by delivery of hard copies of the results.
The challenge in the next decade for laboratory medicine is to accomplish these major changes in organization to meet fiscal restraint and shortage of adequately trained laboratory personnel. Collaborative networks, constructive use of point of care devices, and the development of rapport between laboratories and their clients leading to cost effective utilization of limited resources, are some of the strategies that will maximize patient benefit
Quality control (QC) is a procedure or set of procedures intended to ensure that a manufactured product or performed service adheres to a defined set of quality criteria or meets the requirements of the client or customer. QC is similar to, but not identical with, quality assurance (QA).
QC IN clinical biochemistry labs and hospitals
Quality in clinical laboratory is a continuous journey of improving processes through team work, innovative solutions, regulatory compliance with final objective to meet the evolving needs of clinicians & patients.
QC Multi rules - Improving Laboratory Performance Through Quality ControlRandox
Randox Quality Control's latest educational guide examines and explains what QC Multi-Rules are, How to identify an out of control event with QC rules, How to use QC Multi-Rules, The different types of analytical errors, The tools to assist labs and how a lab can troubleshoot QC errors.
Troubleshooting QC Problems: Your QC has failed, what do you do next?Randox
Randox Quality Control's next 'Improving Laboratory Performance Through Quality Control' educational guide has been published with helpful tips that your laboratory can use in order to ensure it has effective troubleshooting procedures in place.
So you ran QC this morning and realised that one of your analytes has been flagged as 'out-of-control', what do you do next? Do you ignore the warning and continue patient testing, repeat the control until it's within range or do you halt patient testing and investigate the source of the error?
When it comes to troubleshooting QC errors, unfortunately there is no easy path to take. However, it's important that you have standard operating procedures in place, outlining what to do in the event of an out-of control error. Errors occur in laboratories all over the world. A lab with effective troubleshooting procedures in place will still have errors but will be able to detect them, quickly reducing their impact and reducing the risk of wasting both time and money.
Characterization and the Kinetics of drying at the drying oven and with micro...Open Access Research Paper
The objective of this work is to contribute to valorization de Nephelium lappaceum by the characterization of kinetics of drying of seeds of Nephelium lappaceum. The seeds were dehydrated until a constant mass respectively in a drying oven and a microwawe oven. The temperatures and the powers of drying are respectively: 50, 60 and 70°C and 140, 280 and 420 W. The results show that the curves of drying of seeds of Nephelium lappaceum do not present a phase of constant kinetics. The coefficients of diffusion vary between 2.09.10-8 to 2.98. 10-8m-2/s in the interval of 50°C at 70°C and between 4.83×10-07 at 9.04×10-07 m-8/s for the powers going of 140 W with 420 W the relation between Arrhenius and a value of energy of activation of 16.49 kJ. mol-1 expressed the effect of the temperature on effective diffusivity.
Artificial Reefs by Kuddle Life Foundation - May 2024punit537210
Situated in Pondicherry, India, Kuddle Life Foundation is a charitable, non-profit and non-governmental organization (NGO) dedicated to improving the living standards of coastal communities and simultaneously placing a strong emphasis on the protection of marine ecosystems.
One of the key areas we work in is Artificial Reefs. This presentation captures our journey so far and our learnings. We hope you get as excited about marine conservation and artificial reefs as we are.
Please visit our website: https://kuddlelife.org
Our Instagram channel:
@kuddlelifefoundation
Our Linkedin Page:
https://www.linkedin.com/company/kuddlelifefoundation/
and write to us if you have any questions:
info@kuddlelife.org
Climate Change All over the World .pptxsairaanwer024
Climate change refers to significant and lasting changes in the average weather patterns over periods ranging from decades to millions of years. It encompasses both global warming driven by human emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. While climate change is a natural phenomenon, human activities, particularly since the Industrial Revolution, have accelerated its pace and intensity
WRI’s brand new “Food Service Playbook for Promoting Sustainable Food Choices” gives food service operators the very latest strategies for creating dining environments that empower consumers to choose sustainable, plant-rich dishes. This research builds off our first guide for food service, now with industry experience and insights from nearly 350 academic trials.
"Understanding the Carbon Cycle: Processes, Human Impacts, and Strategies for...MMariSelvam4
The carbon cycle is a critical component of Earth's environmental system, governing the movement and transformation of carbon through various reservoirs, including the atmosphere, oceans, soil, and living organisms. This complex cycle involves several key processes such as photosynthesis, respiration, decomposition, and carbon sequestration, each contributing to the regulation of carbon levels on the planet.
Human activities, particularly fossil fuel combustion and deforestation, have significantly altered the natural carbon cycle, leading to increased atmospheric carbon dioxide concentrations and driving climate change. Understanding the intricacies of the carbon cycle is essential for assessing the impacts of these changes and developing effective mitigation strategies.
By studying the carbon cycle, scientists can identify carbon sources and sinks, measure carbon fluxes, and predict future trends. This knowledge is crucial for crafting policies aimed at reducing carbon emissions, enhancing carbon storage, and promoting sustainable practices. The carbon cycle's interplay with climate systems, ecosystems, and human activities underscores its importance in maintaining a stable and healthy planet.
In-depth exploration of the carbon cycle reveals the delicate balance required to sustain life and the urgent need to address anthropogenic influences. Through research, education, and policy, we can work towards restoring equilibrium in the carbon cycle and ensuring a sustainable future for generations to come.
Prevalence of Toxoplasma gondii infection in domestic animals in District Ban...Open Access Research Paper
Toxoplasma gondii is an intracellular zoonotic protozoan parasite, infect both humans and animals population worldwide. It can also cause abortion and inborn disease in humans and livestock population. In the present study total of 313 domestic animals were screened for Toxoplasma gondii infection. Of which 45 cows, 55 buffalos, 68 goats, 60 sheep and 85 shaver chicken were tested. Among these 40 (88.88%) cows were negative and 05 (11.12%) were positive. Similarly 55 (92.72%) buffalos were negative and 04 (07.28%) were positive. In goats 68 (98.52%) were negative and 01 (01.48%) was recorded positive. In sheep and shaver chicken the infection were not recorded.
Willie Nelson Net Worth: A Journey Through Music, Movies, and Business Venturesgreendigital
Willie Nelson is a name that resonates within the world of music and entertainment. Known for his unique voice, and masterful guitar skills. and an extraordinary career spanning several decades. Nelson has become a legend in the country music scene. But, his influence extends far beyond the realm of music. with ventures in acting, writing, activism, and business. This comprehensive article delves into Willie Nelson net worth. exploring the various facets of his career that have contributed to his large fortune.
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Introduction
Willie Nelson net worth is a testament to his enduring influence and success in many fields. Born on April 29, 1933, in Abbott, Texas. Nelson's journey from a humble beginning to becoming one of the most iconic figures in American music is nothing short of inspirational. His net worth, which estimated to be around $25 million as of 2024. reflects a career that is as diverse as it is prolific.
Early Life and Musical Beginnings
Humble Origins
Willie Hugh Nelson was born during the Great Depression. a time of significant economic hardship in the United States. Raised by his grandparents. Nelson found solace and inspiration in music from an early age. His grandmother taught him to play the guitar. setting the stage for what would become an illustrious career.
First Steps in Music
Nelson's initial foray into the music industry was fraught with challenges. He moved to Nashville, Tennessee, to pursue his dreams, but success did not come . Working as a songwriter, Nelson penned hits for other artists. which helped him gain a foothold in the competitive music scene. His songwriting skills contributed to his early earnings. laying the foundation for his net worth.
Rise to Stardom
Breakthrough Albums
The 1970s marked a turning point in Willie Nelson's career. His albums "Shotgun Willie" (1973), "Red Headed Stranger" (1975). and "Stardust" (1978) received critical acclaim and commercial success. These albums not only solidified his position in the country music genre. but also introduced his music to a broader audience. The success of these albums played a crucial role in boosting Willie Nelson net worth.
Iconic Songs
Willie Nelson net worth is also attributed to his extensive catalog of hit songs. Tracks like "Blue Eyes Crying in the Rain," "On the Road Again," and "Always on My Mind" have become timeless classics. These songs have not only earned Nelson large royalties but have also ensured his continued relevance in the music industry.
Acting and Film Career
Hollywood Ventures
In addition to his music career, Willie Nelson has also made a mark in Hollywood. His distinctive personality and on-screen presence have landed him roles in several films and television shows. Notable appearances include roles in "The Electric Horseman" (1979), "Honeysuckle Rose" (1980), and "Barbarosa" (1982). These acting gigs have added a significant amount to Willie Nelson net worth.
Television Appearances
Nelson's char
Willie Nelson Net Worth: A Journey Through Music, Movies, and Business Ventures
Quality Assurance and Quality Control
1. Chapter 12
Quality Assurance and Quality Control
1 Need for Quality Assurance
Many studies have shown that analytical results are often subject to serious errors,
particularly at the low concentrations encountered in environmental samples. In fact, the
errors may be so large that the validity of actions taken regarding management of
environment may become questionable,
Nutrients, N and P, in very small concentrations can cause eutrophication of water
bodies. An analytical quality control (AQC) exercise conducted by United States
Environmental Protection Agency (US-EPA) showed a wide variation in results when
identical samples were analysed in 22 laboratories:
Nutrient Concentration, Range of results,
mg/L mg/L
Ammonia 0.26 0.09-0.39
1.71 1.44-2.46
Nitrate 0.19 0.08-0.41
Total phosphorus 0.882 0.642- 1.407
It is seen that the range of values reported are significantly large,+50% for ammonia
and +100% for nitrates, compared to the actual concentrations, Therefore, the need for
nutrient control programme and its results become difficult to assess.
Many laboratories analyzing water quality report total dissolved salts (TDS) calculated
from the electrical conductivity (EC) value:
/
TDS, mg/L = A x EC, pS/cm
where A is a constant ranging between 0.55 and 0.9 depending on the ionic
composition of salts dissolved in the water.
An inter-laboratory AQC exercise conducted by Central Pollution Control Board (CPCB)
showed that for measurement of EC of a standard solution, out of 44 participating,
laboratories only 34% reported values in the acceptable range. Figure 1.
2. Thus, the reliability of iso-concentrations of TDS in groundwaters, drawn based on data
of several laboratories may become questionable on two counts; use of an arbitrary
value for the constant A and variation in inter-laboratory measurements.
These examples amply demonstrate the need for quality assurance (QA) programmes.
2 Quality assurance programme
For any QA programme it is important to explicitly state, in detail, the quality
requirement of the product, in our case the analytical data, its precision and accuracy.
The QA programme for a laboratory or a group of laboratories should contain a set of
operating principles and procedures, written down and agreed upon by the organisation,
delineating specific functions and responsibilities of each person involved and the chain
of command, which would produce analytical data of required accuracy. It is necessary
that the top management agrees to the 'quality policy'; it requires financial commitment.
The next step is that all levels in the organization accept this concept, the laboratory
supervisor, who is responsible to the data user, the analyst and the field staff.
For effectiveness, QA requires continuing evaluation of the programme and audits. This
may done by an independent group within the organization. The checking of work
should be done on a regular basis, not to reward or reprimand, but to correct mistakes.
It should be based on notion that everybody makes mistakes and one can learn from
one's mistakes. Striving for quality is not equal to striving for perfection. The analytical
data has a good quality when it is fit for use.
Various aspects of a QA programme are noted below.
Sample control and documentation
Procedures regarding sample collection, labelling, preservation, transport, preparation
of its derivatives, where required, and the chain-of-custody.
r
Mistakes in sampling will have an influence on the monitoring results. There is no
possibility to reproduce a sample, there is only a probability based on expert judgement,
that there is little or no change since the erroneous sample was taken. Because of the
importance of proper sampling, special attention should be paid to the motivation of the
staff involved in sampling. Proper training and facilities can help, but also feed back of
monitoring results to the field staff may provide attachment to the programme.
3. Standard analytical procedures
Procedures giving detailed analytical method for the analysis of each parameter giving
results of acceptable accuracy should be clearly defined.
Analyst qualifications
Qualifications and training requirements of the analysts must be specified. The number
of repetitive analyses required to obtain result of acceptable accuracy also depends on
the experience of the analyst.
Equipment maintenance
For each instrument, a strict preventive maintenance programme should be followed. It
will reduce instrument malfunctions, maintain calibration and reduce downtime.
Corrective actions to be taken in case of malfunctions should be specified.
Calibration procedures
In analyses where an instrument has to be calibrated, the procedure for preparing a
standard curve must be specified, e.g., the minimum number of different dilutions of a
standard to be used, method detection limit (MDL), range of calibration, verification of
the standard curve during routine analyses, etc.
Analytical quality control
This includes both within-laboratory AQC and inter-laboratory AQC.
Under the within-laboratory programme studies may include: recovery of known
additions to evaluate matrix effect and suitability of analytical method; analysis of
reagent blanks to monitor purity of chemicals and reagent water; analysis of sample
blanks to evaluate sample preservation, storage and transportation; analysis of
duplicates to asses method precision; and analysis of individual samples or sets of
samples (to obtain mean values) from same control standard to check random error.
Inter-laboratory programmes are designed to evaluate laboratory bias and requires
participation of a reference laboratory.
AQC exercise are not one time exercises but rather internal mechanisms for checking
performance and protecting laboratory work from errors that may creep in. Laboratories
who accept these control checks will find that this results in only about 5 percent extra
work.
In Summary:
AQC is:
• an internal mechanism for checking your own performance
4. • protecting yourself from a dozen of errors that may creep into analytical work
• to avoid human errors in routine work
• practiced by responsible chemists
• not useless work
• common practice in certified laboratories
AQC is NOT:
• much work
• to be carried out for each and every routine sample.
• checking and reporting the quality of your work
• a one time exercise to be forgotten soon
Data reduction, validation and reporting
Data obtained from analytical procedures, where required, must be corrected for sample
size, extraction efficiency, instrument efficiency, and background value. The correction
factors as well as validation procedures should be specified. Results should be reported
in standard units. A prescribed method should be used for reporting results below MOL.
An important aspect of reporting the results is use of correct number of significant
figures. In order to decide the number of significant digits the uncertainty associated
with the reading(s) in the procedure should be known. Knowledge of standard deviation
will help in rounding off the figures that are not significant. Procedures regarding
rounding off must be followed.
3 Shewhart control charts
If a set of analytical results is obtained for a control sample under conditions of routine
analysis, some variation of the observed values will be evident. The information is said
to be statistically uniform and the analytical procedure is said to be under statistical
control if this variation arises solely from random variability. The function of a control
chart is to identify any deviation from the state of statistical control.
Shewhart control chart is most widely used form of control charts. In its simplest form,
results of individual measurements made on a control sample are plotted on a chart in a
time series. The control sample is analysed in the same way as the routine samples at
fixed time intervals, once or twice every week, or after 20 to 50 routine samples. .
Assuming the results for the control sample follow the Normal frequency distribution, it
would be expected that only 0.3% of results would fall outside lines drawn at 3 standard
deviations above and below the mean value called upper and lower control limits, UCL
and LCL, respectively. Individual results would be
5. expected to fall outside these limits so seldom (3 out of 1000 results), that such an
event would justify the assumption that the analytical procedure was no longer in
statistical control, Le., a real change in accuracy has occurred.
Two lines are inserted on the chart at 2 standard deviations above and below the mean
value called upper and lower warning limits, UWL and LWL, respectively. If the method
is under control, approximately 4.5% of results may be expected to fall outside these
lines.
This type of chart provides a check on both random and systematic error gauged from
the spread of results and their displacement, respectively. The following actions may be
taken based on analysis results in comparison to the standard deviation.
Control limit: If one measurement exceeds the limits, repeat the analysis immediately. If
the repeat is within the UCL and LCL, continue analyses; if it exceeds the control limits
again, discontinue analyses and correct the problem.
Warning limit: If two out of three successive points exceeds the limits, analyse another
sample. If the next point is within the UWL and LWL, continue analyses; if the next point
exceeds the warning limits, discontinue analyses and correct the problem.
Standard deviation: If four out of five successive points exceed one standard deviation,
or are in increasing or decreasing order, analyse another sample. If the next point is
less than one standard deviation away from the mean, or changes the order, continue
analyses; otherwise discontinue analyses and correct the problem.
Central line: If six successive points are on one side of the mean line, analyse another
sample. If the next point changes the side continue the analyses; otherwise discontinue
analyses and correct the problem.
Figure 2 to Figure 4 illustrate some of the cases of loss of statistical control for analysis
of individual samples based on the above criteria.
4 Discussion of results
Precision
The most important parameter to evaluate in the results is the precision. The statistical
term to evaluate precision is standard deviation. The numerical value of the standard
deviation depends on the average concentration Numerical values of standard
deviations of low concentration solutions are usually smaller than those of solutions with
higher concentrations. Therefore the coefficient of variation, should be used to evaluate
precision. This is particularly useful when comparing results of analysis for samples
having different concentrations.
For example, for results of two sets of analyses, performed on two different samples, if
the mean values are 160 and 10 mg/L and standard deviations are 8 and 1.5 mg/L,
respectively, comparison of standard deviation would indicate lower precision for the
6. first set of observations (standard deviation 8 mg/L), while the CV values work out to be
5 [(8/160) x 100] and [15 (1.5/10) x 100] percents respectively, indicating a lower
precision for the second set of observations.
Before evaluating the results one should answer the question 'what is the desired
precision for an analysis?'. In fact this question should be answered by the so called
'data users'. The use of the data determines the required precision, e.g. detection of
trends may require more precise results in order to actually detect small changes with
respect to time.
As a minimum goal for precision, however, the precision that can be obtained by
correctly and adequately following the prescribed method should be adopted.
Calculating revised limits when continuing the exercise
Warning and control limits should be recalculated periodically. Especially when new
techniques are introduced, the precision improves when experience is gained with the
technique. A good time for recalculating the control and warning limits is at the time
when the control chart is full and a new graph has to be created anyway. At this point,
use the 20 most recent data on the old chart for construction of LCL, LWL, average,
UWL and UCL.
Errors that cannot be detected by within-laboratory AQC
The within-laboratory AQC exercise focuses mainly on precision. A laboratory on its
own cannot detect many sources of bias. If the analytical balance in a laboratory always
reads 10% too much all solution prepared will have a 10% higher concentration: For
example, in the hardness determination by titrimetric procedure the standard CaC03
solution, the EDTA titrant and also the control sample containing CaC03 will all have
10% higher concentration and therefore the error will not be detected. This error can
only be detected by analysing a sample prepared by a laboratory with a correctly
functioning balance. The current laboratory will underestimate the concentration of such
a inter-laboratory sample also by 10% because their EDTA titrant would be' 10% too
strong'.
In some cases freshly introduced bias may be detected. For example, if the
measurements consistently fall on one side of the previously calculated mean, it
indicates a freshly introduced bias. An inter-laboratory AQC exercise should be
conducted for detecting bias or accuracy for analysis.