Lecture (5): lab methods of measurement
Lecture (5): lab methods of measurement
Lecture (5): Lecture objectives:
By the end of this lecture students should be able to:
1. To know the water sampling techniques . 2. To know the water quality analytical
methods.
Lecture (5): lab methods of measurement,
Data Quality Objectives (DQO):
DQOs can be defined as those sampling and analytical objectives that provide the number of samples and the quality of results needed to satisfy the decision making process.
Sampling techniques
Steps should be taken during the taking, handling, transportation, storage and analysis of water to ensure that the sample is:
1. representative of the quality of the water;
2. not contaminated .
3. kept at such a temperature and in conditions that will ensure there is no material change in the sample;
4. analyzed as soon as possible;
5. analyzed by a laboratory with a verified quality control system.
Analytical Methods For Inorganic Constituents:
The analytical methods for inorganic constituents in water for environmental monitoring are commonly subdivided into:
Wet chemistry
Metals
Wet Chemistry
Wet chemistry methods are the classical bench methods and include common water quality parameters [i.e., pH, biochemical oxygen demand (BOD), hardness, and alkalinity] utilizing:
A. colorimetric, B. potentiometric, C. gravimetric,
D. titration,
E. chromatographic determinations.
These methods have varying degrees of sensitivity and accuracy.
Metals
Techniques for the analysis of trace-metal concentrations these techniques include such as Flame Atomic Absorption spectrometry (FLAA),
These methods has advantages and disadvantages that should be addressed before selection of an analytical procedure.
Analytical Methods For Organic Constituents:
The decision of which method to utilize is determined by regulations, desired data quality, and cost. Organic chemical methods can be divided into:
those that determine total organic matter present and
individual organic compounds or groups of compounds.
Total Organic Matter Present:
Total organic methods measure such parameters as:
1. Biochemical oxygen demand (BOD), 2. Chemical oxygen demand (COD),
3. Total organic carbon (TOC), 4. oil and grease,
5. total recoverable petroleum hydrocarbons (TRPH), 6. Total phenols.
Individual Organic Constituents or Groups
A very detailed discussion would be needed to address the methods used to analyze the vast numbers of naturally occurring and man-made organic compounds found in water. EPA SW-846 provides a good listing of methods. Internet services, such as Toxnet (http://
toxnet.nlm.nih.gov/), can also be useful tools.
Toxnet is a cluster of databases on toxicology, hazardous chemicals, and related areas.
Indicator microorganisms
Indicator microorganisms such as total coliform, fecal coliform, fecal streptococci and E-coli are used to indicate the possibility of sewage pollution in the water. The higher the coliform bacteria concentration, the higher the possibility of having pathogens in water. Due to the difficulty to diagnose pathogens, indicator organisms are used instead.
Measuring pH
• Using a meter
“Calibrate the probe and meter according to the manufacturer’s directions. Use of two buffers (pH 7 and 10) for calibration is recommended.”
The LaMotte SMART 2 Colorimeter
A Computerized Way to Conduct Water
Quality Analysis while using Light to Analyze the Intensity of
Chemical Reactivity.
The results are direct readings.
Titration for O
2• Dissolved Oxygen is
sometimes referred to as DO
• The titration method to measure DO is called the Winkler Titration
• Once you get to the fixed stage, it could be analyzed using the colorimeter
Conductivity: Meter
Measuring the conductivity is an accurate way to determine
salinity.
Conductivity of ions is measured using the following two units…
Freshwater = micro Siemens (uS) Saltwater = milli Siemens (mS)
Principle of Light
Visible Light is a part of the electromagnetic spectrum with a range of 350 – 720
nanometers (nm)
