2Week 1 Objectives Proper Sample Collection Reading assignment:American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF) Standard Methods for the Examination of Water and Wastewater, 20th editionProper Sample CollectionUnderstand basic statistical conceptsGrasp QA/QCUnderstand IDL, MDL, and LDL, and how to calculate themUse Excel spreadsheet for lab analysisUnderstand the role of alkalinity in water and waste waterUnderstand how to measure alkalinity (SM #2010)
4Sample Collection #1060Grab Sample: Grab samples are single samples collected at a specific spot at a site over a short period of time (typically seconds or minutes). Thus, they represent a ‘‘snapshot’’ in both space and time of a sampling areaComposite Sample: Composite samples should provide a more representative sampling of heterogeneous matrices in which the concentration of the analytes of interest may vary over short periods of time and/or space .Representative Sample: sample should represent the whole distribution sample
5Sample Collection #1060Why is proper collection of a sample important?It is an old axiom that the result of any testing method can be no better than the sample on which it is performed.Why do we care?The analysis will govern sample collection.
6Sample Collection #1060 Sample deterioration? Sample collection? Obtain a sample that meets the requirements of the sampling program and handle it so that it does not deteriorate or become contaminated or compromised before it is analyzed.Sample collection?Clean sample bottles especially when sampling and analyzing for very low analyte levels.Collect a 1-L sample for most physical and chemical analyses. Keep coolRepresentative samplePre-rinse only if no preservative addedLeave no head space
7Sample Collection #1060 Field Sampling Noncomposite samples for acidity, alkalinity,chlorine residual, nitrate, dissolved oxygen,temperature, and pH. All on ice!BOD analysis=composite=refrigerateMicrobial analysis= no composites=on iceNote: Field Observations are critical!water temperature, weather conditions, water level, stream flow, post-collection conditions
8Sample Collection #1060 Things to keep in mind…. Avoid areas of excessive turbulenceAvoid sampling at weirsCollect samples beneath the surface inquiescent areas and open sampling container below surface with the mouth directed toward the currentComposite samples are required, ensure that sample constituents are not lost during compositing.Be safety consciousLabel samples adequately CHAIN OF CUSTODY!!
9Water Distribution Sample Collection Samples must be representative of the water distribution system.Water taps used for sampling should be free of aerators, strainers, hose attachments, mixing type faucets, and purification devices.Cold water taps should be used.The service line must be cleared before sampling by maintaining a steady water flow for at least two minutes (until the water changes temperature).At least 100 mL of sample must be collected, allowing at least a 1-inch air space to facilitate mixing of the sample by shaking.Immediately after collection, a sample information form should be completed= CHAIN OF CUSTODY
10Water Distribution Sample Collection · Name of system (public water system site identification number, ifavailable)· Sample identification (if any)· Sample site location· Sample type (e.g., routine distribution system sample, repeat sample, rawor process water, other special purpose sample)· Date and time of collection· Analysis required· Disinfectant residual· Name of sampler and organization (if not the water system)· Sampler's initials· Person(s) transporting the samples from the system to the laboratory (ifnot the sampler)· Transportation condition (e.g., <10°C, protection from sunlight). If acommercial shipper was used, shipping records should be available.· Any remarks
11Which of the following terms refers to the addition of chemicals to a sample in the field to prevent water quality indicators from changing before final measurements are performed?StandardizationBufferPreservationTitration
12A ____ sample is a discrete sample that is collected manually. GrabCompositeFlow proportionalTemporal
13A ________ sample consists of a collection of individual samples collected at regular intervals throughout the dayCompositeGrabWeighted averageFinal effluent
14A single sample of water taken at one time from one place is called a _________ sample. GrabCompositeRepresentative
15Samples should only be collected where the water is ______ ____________. Well mixedOverflowing weirsBetween processesStanding quietly
16_______ of ________ is a legal term for an unbroken sequence of possession from sample collection through analysis.Chain CustodyChain CommandChain Sample
17One mL is what fraction of a L? 1/101/1001/10001/100000
18What is the most common preservation method for samples? Cooling to 4 deg. CDechlorinationReductionAcidification
199/5(degrees C) + 32 = ______CelsiusFahrenheitKelvin
25Statistics Key Words/Equations Mean: is simply the sum of all values divided by the number of valuesµ = (∑ixi)/nStandard Deviation: is a measure of the spread of valuesσ = [∑(x−µ)2/n]1/2.Coefficient of Variation: normalizes the standard deviation and sometimes facilitates making direct comparisons among analyses that include a wide range of concentrations σ/µ, with its estimate s/xMedian: middle value of a sample populationMode: most frequently occurring number in a sample population
26Another word for the average is the ______________? MeanNormGeometric meanHighest probability
27The mode is the most frequently occurring number in a data set? TrueFalse
28Statistics Key Words/Equations Accuracy: combination of bias and precision of an analytical procedure, which reflects the closeness of a measured value to a true value.Precision: measure of the degree of agreement among replicate analyses of a sample, usually expressed as the standard deviation
29Statistics QA/QC KeyQuality assessment: procedure for determining the quality of laboratory measurements by use of data from internal and external quality control measuresQuality assurance: a definitive plan for laboratory operation that specifies the measures used to produce data of known precision and bias.Quality control: set of measures within a sample analysis methodology to assure that the process is in control.
30QA Steps QC Steps Appropriate signatures Test Performed by Laboratory Sample Handling Procedures ChecklistStandard Operating ProceduresData Verification PracticesChain of custodyQC StepsShow yearly results of MDLRun Internal BlankRun duplicatesInternal StandardsBlind SamplesRoutine Calibration
31Quality control samples are analyzed for all of the following reasons EXCEPT: Check for ContaminationVerify precisionVerify accuracyDetermine if interferences are present.To boost the ego of the analyst.
32Normal DistributionNormal Distribution: If a measurement is repeated many times under essentially identical conditions, the results of each measurement, x, will be distributed randomly about a mean value (arithmetic average) because of uncontrollable or experimental error.68.27% of the measurements lie between µ ± 1σ95.45% between µ ± 2σ,99.70% between µ ± 3σ.It is sufficiently accurate to state that 95% of the values are within ±2σ and 99% within ±3σ.
33AverageAverage: Two feet in bucket of ice water, two feet on hot coals.On average I feel great?
34Accuracy and Precision Accuracy: refers to how closely a measured value agrees with the correct value.Precision: refers to how closely individual measurements agree with each other.**Assume aim is directed at bulls eye*accurate (the average is accurate) not preciseaccurate and preciseinaccurate not preciseprecise not accurate
35Analytical PrecisionInstrumental detection level (IDL): the constituent concentration that produces a signal greater than five times the signal/ noise ratio of the instrument.1.645 times the standard deviation of the blankMethod detection level (MDL): For seven replicates of the sample, the mean must be 3.14s above the blank where s is the standard deviation of the seven replicates. The method detection limit (MDL) is the only one designed to be determined in your laboratory using your chemicals, equipment, and technicians.Compute MDL from replicate measurements one to five times the actual MDL. The MDL will be larger than the LLD because of the few replications and the sample processing steps and may vary with constituent and matrix.Lower level of detection (LLD): the constituent concentration in reagent water that produces a signal3.219s above the mean of blank analyses
36Analytical Precisionminimum quantitation level (MQL): the constituent concentration that produces a signal sufficiently greater than the blank that it can be detected within specified levels by good laboratories during routine operating conditions.Typically it is the concentration that produces a signal 10s above the reagent water blank signal.
37Both of these quality control samples can be used to measure accuracy and precision. Standards and DuplicatesBlanks and StandardsBlanks and DuplicatesDuplicates and Spikes
38This type of quality control sample is used to check for interferences. SpikesDuplicateStandardsBlanks
39Relative Standard Deviation Relative standard deviation (RSD): is a measure of precision, calculated by dividing the standard deviation for a series of measurements by the average measurement.RSD= σ/µCV = σ/µ *100CV % Rule of Thumb For WQT 1340-5% =excellent precision5-10% =acceptable precision10-20%= Poor precision20%>=Houston we have a problem!
40Duplicates should agree with their original samples by this margin. Plus or Minus 20% Relative Percent DifferencePlus or Minus 10% Relative Percent DifferencePlus or Minus 20%Plus or Minus 10%
41The statistical calculation done to determine the spread of a set of measurements is called the ______________.Standard DeviationRelative Pervasive DifferencePercent DeviationStandard Error
42Problem #1 Calculate mean= 7.2+7.0+6.9+5.5+7.3 = 6.78 5 Some WQT 134 students measure pH on the same sample! The results are as follows:AB= 7.2DO=7.0KO=6.9ML=5.5EC=7.3Calculate mean= = 6.785
44Problem #1, STDEV, Excel continued Calculate standard deviation=σ = [∑(x−µ)2/n]1/2.
45Problem #1, RSD, Excel continued Calculate RSDRSD= σ/µ
46Problem #1, CV, Excel continued Calculate CVCV= σ/µ * 100
47Problem #1, Final Analysis, Excel continued CV % Rule of Thumb For WQT 1340-5% =excellent precision5-10% =acceptable precision10-20%= Poor precision20%>=Houston we have a problem!
48Problem #2, IDLInstrumental detection level (IDL): the lowest limit that the instrument can detect. It is determined on samples which have not gone through any sample preparation steps.AB= mg/LDO=.0023 mg/LKO=.0026 mg/LML=.0027 mg/LEC=.0025 mg/LCalculate IDL=1.645 X standard deviation of the blankIDL=1.645* = mg/L
49Problem #3 MDLOne of the procedures outlined in 40 CFR 136 for determining the MDL is to prepare the analyte concentration at a level one to five times the estimated detection limit and run it multiple times.Make solution of the analyte that is one to five times the estimated detection.2. Test this solution seven or more times, then determine the standard deviation of the data set.3. The method detection limit is calculated according to the formula:MDL = Student’s t value (from a table) x standard deviation.
50Problem #3 MDL A IDL for a phosphate procedure is 0.045 mg/L. Make a solution of mg/L phosphate, which is approximately four times the estimated limit2. Results of multiple analysis (mg/L)0.190, , 0.166, 0.174, 0.149, 0.183, 0.153, 0.144, 0.1733. Determine STDEV0.019 = mg/L.4. Use MDL equation:MDL = Student’s t value (from table) x std. deviation= x mg/L= mg/L
52Problem #4 LDLThe lowest limit is actually 2.5 times higher than the MDL.1. Use LDL equation:LDL = 2.5 X MDL= 2.5 X mg/L = 0.14 mg/LThe lowest possible value that can be detected with this method is 0.14 mg/L anything below this value is suspect!
53Today’s objective: to become proficient with sample collection and statistical analysis has been met.Strongly AgreeAgreeNeutralDisagreeStrongly Disagree
54To improve my knowledge pertinent to the subject matter I would like to?? Have the instructor provide more math/stats blackboard homework assignmentsHave data available on the webpage in Excel to practice my analysisHave the instructor provide more blackboard reading assignmentsHave a quiz to review the subject matterNone of the above