Chapter 1 of Standard Methods for the Examination of Water and Wastewater
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Transcript of Chapter 1 of Standard Methods for the Examination of Water and Wastewater
CHAPTER 1STANDARD METHODSKatie Indarawis
TABLE OF CONTENTS (OUTLINE)
Statistics Quality Assurance (Quality Control and
Quality assessment) Data Quality Method Development and Evaluation Expression of results Collection and preservation of samples Reagent Water Health and Safety Waste minimization and disposal
STATISTICS
Normal Distribution Standard Normal Curve Confidence Interval Standard error Relative standard deviation or Coefficient of
variation Outliers
STATISTICS: CONFIDENCE INTERVALS
Typically small sample sizes, so confidence intervals of the mean are expressed as:
Where t has the following values for 95% confidence limits:
𝑥± 𝑡𝑠
√𝑛
1010 B
STATISTICS: NORMAL DISTRIBUTION
Standard Deviation – spread of the distribution
𝜎=[∑ (𝑥−𝜇)2
𝑛 ]12
𝑠=[∑ (𝑥−𝑥)2
𝑛−1 ]12
1010 B
STATISTICS: RELATIVE ST. DEV. (CV)
Relative Standard Deviation (or coefficient of variation) – expressed as a percentage
Normalizes the standard deviation
Measure of variability
1010 B
STATISTICS: OUTLIERS
Outliers
Compare the value of T to a t-test table at either a 1% or 5% level of significance (if T is larger than t-test statistic, then the value is an outlier).
for a high value
for a low value
1010 B
TABLE 1010:I
QUALITY ASSURANCE
A set of operating rules: Standard operating procedures (SOP) Training requirements Number of analyses required
Equipment preventative maintenance procedures Calibration procedures, corrective actions, internal
quality control activities, performance audits, and data assessments for bias and precision.
1020 A
QUALITY CONTROL
Certification of operator competence Recovery of known additions Analysis of externally supplied standards Analysis of reagent blanks Calibration with standards Analysis of duplicates Maintenance of control charts
1020 B
QUALITY CONTROL (QC) CALCULATIONS
Initial calibrations:
QC CALCULATIONS
Calibration verification
QC CALCULATIONS
Duplicate sample:
CONTROL CHARTS
QUALITY ASSESSMENT
Using internal and external quality control measures
Includes: Laboratory check samples Laboratory intercomparison samples Compliance audits Internal QC described previously
Applied to test the recovery, bias, precision, detection limit, and adherence to SOP requirements
1020 C
DATA QUALITY Indicators of data quality are bias and precision
(when combined, express its accuracy)
1030 A
BIAS VS PRECISION
Bias – A measure of systematic error (part from the method, part from the lab’s use of the method)
Precision – Measure of the closeness with which multiple analysis of a given sample agree with one another. OR, random error.
1030 A
MEASUREMENT UNCERTAINTY Biases that can occur in the system of analysis:
Weighing a sample Result produced by the analytical instrument Changes in quality of reagents Incomplete extraction
Generally the instrumental and extraction biases (B) are the greatest, so the equation simplifies to:
To express with 95% confidence:
1030 B
MEASUREMENT UNCERTAINTY
Combined concepts of repeatability and reproducibility (Gage R&R):
1030 B
METHOD DETECTION LIMIT
The smallest amount that can be detected above the noise in a procedure and within a stated confidence limit is a detection limit.
The confidence limits are set to reduce Type I and Type II errors.
Instrument Detection Limit (IDL) Lower Limit of Detection (LLD) Method Detection Limit (MDL) Limit of Quantitation (LOQ)
1030 C
DATA QUALITY OBJECTIVES Stating the issue
Reason for performing analysis Identifying possible decisions and actions
Specific to the research questions Identifying inputs
Identify what information is needed Identifying study limits
Logistical issues, time frame, geographical location, etc. Developing a decision rule
Define the parameter, threshold values, criteria for action Specifying limits on decision errors
Sample design errors, measurement errors – Use hypothesis testing
Optimizing the design for collection Identify the most resource-effective design for the study1030
D
CHECKING CORRECTNESS OF ANALYSES
Anion-Cation Balance (electrically neutral) Measured TDS = Calculated TDS
Acceptable ratio: Measured EC = Calculated EC
Acceptable ratio: Measured EC and Ion Sums
100 * anion (or cation) sum, meq/L = (0.9-1.1) EC Calculated TDS to EC Ratio
Calculated TDS/conductivity = 0.55-0.7 Measured TDS to EC Ratio
Acceptable ratio is from 0.55-0.7
1030 F
UNITS
Record only the significant figures In solid samples and liquid wastes of high
specific gravity, make a correction if the results are expressed as ppm or % by weight:
1050 A
SIGNIFICANT FIGURES
Ambiguous zeros If a buret is read as “23.60 mL”, the zero should not be
dropped b/c the analyst took the trouble to estimate the second decimal place.
Standard deviation Round off data points based off of the standard
deviation Calculations
When multiplying or adding numbers, round to the number that limits the accuracy of the number the most (the “weakest link in the chain”)…the one with the least number of significant figures
1050 B
COLLECTION/PRESERVATION OF SAMPLES
Rinse bottle 2-3 times before filling (unless there is a preservative or dechloronating agent)
Leave 1% air space if shipping, etc. Do not remove suspended solids from the sample,
but treat them appropriately Lakes and reservoirs are subject to considerable
variations – choose location, depth, and frequency with care
Avoid turbulent sampling locations
1060 A
COLLECTION/PRESERVATION OF SAMPLES
General precautions Safety considerations (beware of toxic
substances) Types of samples
Grab samples Composite samples Integrated samples
Sampling Methods Manual sampling Automatic sampling Sorbent sampling
Sample containers1060 A
TYPES OF SAMPLES
Grab – use when a source is known to be constant in composition over a considerable period of time or over a substantial distance in all directions
Composite samples (time composite) – most useful for determining average concentrations, usually over a 24 hr period.
Integrated samples – most useful when you need a maxima and minima
1060 B
NUMBER OF SAMPLES
Where:N = number of samplest = Student-t statistic for a
given confidence levels = overall standard
deviationU = acceptable level of
uncertainty1060 B
SAMPLE PRESERVATION
Nature of sample changes Know your sample and how it interacts with its
environment Time interval between collection and analysis
For composite samples, use the end of the composite collection as sample time
Depends on the character of the sample, the analysis to be made, and the conditions of storage
Preservation techniques Most of the time, storage at 4ᴼC is recommended Refer to Table 1060:I
1060 C
LABORATORY APPARATUS
Refer to Table 1060:I to make sure you are using the appropriate material for storage
For general lab use, borosilicate glass is most suitable Use class A volumetric glassware for accurate work Dry all anhydrous reagent chemicals in an oven at
105-110ᴼC for at least 24 hrs (preferably overnight) and cool in a desiccator
“1 + 9 HCl” denotes that 1 volume of concentrated HCL is to be diluted with 9 volumes of DI
1060 A-C
LABORATORY TECHNIQUES
Ion Exchange Colorimetric Determinations Other methods
Atomic absorption spectrometry Flame photometry Inductively coupled plasma (ICP) Potentiometric titration Selective ion electrodes Gas chromatography (GC) or GC-mass spec (GCMS) Continuous-flow analysis Ion chromatography
1070 D
REAGENT-GRADE WATER
Reverse osmosis, distillation, and deionization in various combinations can produce reagent-grade water
Ultrafiltration and/or UV treatment may also be used as part of the process
High – Use in test methods requiring min interference and bias and max precision
Medium – The presence of bacteria can be tolerated. Used for the preparation of dyes, reagents, and staining.
Low – Used for glassware washing, etc.
1080 A-C
SAFETY EQUIPMENT
LAB EQUIPMENT:
Fire extinguishers Fire blankets Safety showers Eye washes Safety Shields Safety containers Storage facilities Laboratory fume hoods Chemical spill kits Safety wall chart
PERSONAL PROTECTIVE EQUIPMENT:
• Clothing• Gloves• Safety shoes• Safety glasses• Respirators
1090 B
LABORATORY HAZARDS
Prohibit eating, drinking and smoking Avoid floor clutter so escape routes and fire
extinguishers aren’t blocked Chemical Hazards (next slide) Biological Hazards (properly dispose of pipette
tips, clean tabletops, autoclave for sterilization, etc.)
Radiation Hazards (shield UV lights) Physical Hazards (electrical, mechanical, &
compressed gases)
1090 C
CHEMICAL HAZARDS
Avoid splashing or container spills Inorganic acids and bases
Store acids and bases separately Do everything in the fume hood Add acids/bases to water (not vice versa) Leather will hold acids/bases & continue to burn if
reworn Flush eyes for 15 min, if eye contact occurs
Metals and inorganic compounds In general, consider all lab chemicals as hazardous and
use only as prescribed Organic solvents and reagents
1090 C
HAZARD MANAGEMENT PRACTICES
Properly label hazardous waste containers Provide fire protected storage Use metal safety cans for waste solvents and
segregating incompatible materials Check the MSDS before using new chemicals
1090 D
QUESTIONS?