Environmental Pollutant Monitoring (Second Edition)

Author: Chen Shangqin
Editor-in-Chief: Wang Zhiguang
Publisher:
Publish Date: 2004-07-27
Features:
Content Summary The book is divided into five chapters, covering topics such as the technical preparation for monitoring environmental pollutants, the collection and processing of environmental pollutant samples, the monitoring of non-metallic pollutants, the monitoring of organic pollutants, and the monitoring of metallic pollutants. In terms of monitoring methods, it focuses on introducing chemical analysis methods that are easy to operate and do not require special instruments. This book can serve as a reference for environmental protection management workers, environmental monitoring personnel, environmental science and technology personnel, and teachers and students of relevant majors in colleges and universities.
Excerpt:
Chapter Technical Preparation for Monitoring Environmental Pollutants
Monitoring environmental pollutants is the process of determining representative values of pollutants in the environment. The determination of these representative values is influenced by multiple factors. Due to the wide variations in the state and valence of pollutants, the presence of many interference factors during analysis, and the extremely low concentrations of pollutants, issues such as the selection of monitoring sites, the selection of monitoring items, sampling time, sampling methods, analytical methods, and data processing all require careful attention. Additionally, higher requirements must be placed on the analytical techniques for environmental pollutants. Technical preparation before pollutant monitoring is crucial to ensure the smooth progress of monitoring work and obtain accurate analytical results.
Section Analytical Vessels
I. Selection and Use of Common Analytical Vessels
The selection of common analytical vessels depends on their intended use and requirements. Generally, common analytical vessels refer to glass vessels, ceramic vessels, plastic vessels, and metal vessels.
(1) Glass Vessels
Glass can be categorized into soft glass (common glass), hard glass, and quartz glass. Common glass contains soluble silicates, has poor chemical corrosion resistance, strong adsorption, a high coefficient of thermal expansion, and is prone to cracking due to sudden temperature changes. Therefore, vessels made of common glass are typically used only for titrations with dilute acids and bases. Hard glass contains fewer soluble impurities, has a smaller coefficient of thermal expansion, and is convenient for heating treatment. Hard glass vessels are suitable for general quantitative chemical element analysis. Quartz glass, primarily composed of silicon dioxide, has strong chemical corrosion resistance, an extremely small coefficient of thermal expansion, a high melting point, but is expensive. Quartz vessels are generally used for trace element analysis due to their cost.
(2) Ceramic Vessels
Ceramic vessels are made from high-quality alumina fired at high temperatures. They have superior physical properties and chemical corrosion resistance compared to glass vessels, but alkali reagents cannot be placed in ceramic vessels for high-temperature ignition or fusion, as severe corrosion may occur. Hydrofluoric acid also corrodes ceramic vessels. Ceramic vessels remain unchanged in quality even when heated to 1200°C, making them commonly used as weighing containers in gravimetric methods. When using a large number of ceramic vessels, to prevent errors and confusion, a 500 g/L ferric chloride solution can be used to mark the vessels, allowing them to air dry or bake until the mark is firmly set.
(3) Plastic Vessels
Plastic vessels are generally made from materials such as polyethylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene. Plastic vessels have strong corrosion resistance to fluorides and alkaline solutions. When the solution or sample corrodes glass vessels, plastic vessels should be used instead, especially for the analysis of potassium, sodium, and trace elements. However, plastic vessels are not suitable for storing samples for oil, acid, and organic substance measurements.
(4) Metal Vessels
Metal vessels are mostly crucibles used in analytical work. Crucibles include iron crucibles, nickel crucibles, silver crucibles, and platinum crucibles.
1. Iron Crucibles
Iron crucibles are not easily eroded by sodium peroxide and are inexpensive, making them commonly used when melting samples with sodium peroxide. Before use, it is advisable to perform surface passivation treatment on iron crucibles. After treatment, the iron crucibles can be used as nickel crucibles. The treatment method involves first rinsing the iron crucible with dilute hydrochloric acid, then scrubbing the surface with fine sandpaper, immersing it in 5% dilute sulfuric acid and 5% dilute nitric acid for a few minutes, rinsing and drying, and then igniting in a muffle furnace at 300–400°C for 10 minutes.
2. Nickel Crucibles
Nickel is prone to oxidation when burned in air, making it unsuitable for igniting precipitates for weighing. However, nickel crucibles can resist corrosion from alkaline substances, and alkaline fluxes such as sodium hydroxide, sodium carbonate, sodium bicarbonate, and potassium nitrate can be fused in nickel crucibles. However, sodium peroxide has a corrosive effect on it. Alkaline fluxes containing sulfur, such as potassium bisulfate and potassium persulfate, cannot be fused in nickel crucibles. Molten tin, lead, zinc, and other metal salts can react with nickel crucibles, making them brittle. Mercury salts and borax should not be ignited in nickel crucibles.