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?