In industrial water conditioning, chemical analyses are needed to govern the treatment processes. Analysis should be conducted promptly after sample collection so that the chemical nature of the sample does not change. On-site testing may be supplemented by plant central laboratories or 91大神Water Technologies & Solutions' Customer Service Laboratories.
The methods included in this handbook are suitable for on-site analysis. They involve the use of?apparatus?and chemicals that are evaluated, approved, and supplied by 91大神Water Technologies & Solutions. Lists of required materials are provided with each titrimetric, spectrophotometric, and colorometric procedure. In some cases, other appropriate equipment may be substituted for the apparatus listed. Substitution of reagents, unless otherwise noted, is not recommended. Microbiological tests and tests which are not suitable for on-site analysis have been excluded from this text.
Several authoritative sources have been referenced in the development of these procedures. These sources include The Annual Book of ASTM Standards and the APHA-AWWA Standard Methods for the Examination of Water and Wastewater, along with other well known and widely accepted analytical methodology. The procedures are not for EPA or governmental reporting purposes and are not to be used where litigation may be involved.
SAMPLE COLLECTION AND PREPARATION
In order to ensure that results obtained from an analysis are useful, it is necessary to secure a representative sample from the system to be tested. Sample lines must be flushed before samples are taken, and all sampling locations and procedures must be well defined.
For most tests, the samples should be cooled to room temperature (21-26°C, 70-80°F) prior to testing. They should also be filtered through 0.2-2.5 ?m filters, if required.
Titration Methods
Historically, titration has been the most common method of plant control analysis. Titration is based on the use of a buret, from which a standard solution is added to the sample until an "end point" is reached. The end point is generally indicated by a color change or detected by potentiometric device (e.g., pH meter).
Several types of burets are available for plant use:
- semimicro burets (2.0 or 3.0 mL capacity) are used to titrate low concentrations of species in the sample
- large burets (25 or 50 mL capacity) are used to titrate species found in higher concentrations
- automatic burets feature a reservoir for "automatic" filling of the buret and an overflow and reset to 0 mL
Digital titrators provide a more portable approach to titration in the field. These hand-held units are widely accepted because they are rugged and easily carried from one location to another. The digital titrator is equivalent to a buret in the conventional titration methods. The titrator acts as a plunger and forces concentrated titrant from an attached plastic cartridge. Each cartidge can perform the same amount of testing as one quart of titrant in conventional tests. However, in most plant laboratories and testing locations, automatic burets are still being used.
Photometric Methods
Photometers or spectrophotometers provide the most accurate means of measuring the color of a reacted sample. In field analysis applications, simple filter photometers have been replaced by monochromator-based spectrophotometers. The?essential components of a spectrophotometer?include the following:
n a stable source of radiant energy
- a system of lenses, mirrors, and slits that define, collimate (make parallel), and focus the beam
- a monochromator, to resolve the radiation into component wavelengths or "bands" of wavelengths
- a transparent container to hold the sample
- a radiation detector with an associated read-out system
Light from a tungsten bulb is reflected off of a parabolic mirror and dispersed with a double pass through a high-dispersion prism. The se-lected wavelength is imaged onto a movable slit, ensuring a uniform band width.
Colorimetric Methods
Colorimetric comparator tests are not as accurate as the photometric or spectrophotometric methods. Color comparisons may be used as a backup to on-line or other optical instrumentation. Colorimetric methods have become popular because of their simplicity and relatively low cost. However, tight control of most industrial water systems should not be entrusted to this technique alone.
In a comparator test, a color is developed that is proportional to the concentration of the substance being determined. The concentration present in the sample is determined by comparison with sealed color standards. The color standards are made of colored plastic or glass, or liquids sealed in air-tight containers.
INSTRUMENTAL METHODS USED IN THE LABORATORY
Common new methods of water analysis often involve highly sophisticated electronic instrumentation not generally used on-site for plant control.
- Ion Chromatography is used to measure trace levels of anions in feedwater, steam, condensate, and boiler water.
- Atomic Absorption Spectroscopy (AA), Inductively Coupled Ion Spectroscopy (ICP), X-ray Fluorescence Spectroscopy, and other laboratory procedures are used routinely to measure many elements at trace levels in a fraction of the time required for wet chemical methods. Some instruments can provide concurrent read-outs of over 40 elements in ppb measurements.
- Gas Chromatography (GC), or Gas Chromatography and Mass Spectroscopy (GC/MS), quantitatively separates and detects volatile components (e.g., neutralizing amines) in boiler condensate.
- High-Pressure Liquid Chromatography (HPLC) permits the separation and detection of trace organic compounds in antimicrobial applications.
- Total Organic Carbon (TOC) measurements are used to determine the amount of organic compounds present in water as a result of water treatments or process leaks. This process is also useful for measuring organic fouling of resinsin demineralizer systems.
- Nuclear Magnetic Resonance Spectroscopy (NMR) provides an analytical tool to aid in determining the structure of organic polymers and other organic water treatment chemicals.
- Fourier Transform Infrared Analysis?(FT-IR) permits the qualitative and quantitative determination of the composition of boiler and cooling system deposits.
- Specific ion electrode detection is an electrometric method that can measure trace amounts of both anions and cations in water and is within the reach of most laboratories and testing sites.
The field-testing methods presented in this handbook are often supplemented by these instrumental methods to optimize treatment effectiveness.
Figure 39-1 Water analysis field test kit.
Figure 39-2. Schematic diagram for DR2000 spectrophotometers.
Figure 39-3. FT-IR microscopy.
