Wet chemical analysis involves determining and measuring the desired elements present in a liquid sample using various methods. It can be categorized into qualitative analysis, which identifies the elements, and quantitative analysis, which determines their quantity. By utilizing chemical reagents, the analyte can be converted into a dye in proportion, which can be visually or photometrically measured.

Wet chemical analysis encompasses a wide range of techniques, including titration, distillation, spectrophotometry (UV/Vis/IR), colorimetry, filtration, drying, weighing, pH tests, and direct read with electrodes. Some of these methods may be more labor-intensive than other techniques since automation cannot be applied to all of them.

PH MEASUREMENTS

pH is a measure of the concentration of free hydrogen and hydroxyl ions in water, representing the acidity or alkalinity of a solution on a scale from 0 to 14, with 7 being neutral. It is a crucial test conducted in laboratories as numerous physical, chemical, and biological processes depend on pH. The most precise pH measurement is obtained using a pH meter, which measures the voltage difference between two electrodes immersed in a solution. To ensure accurate and consistent results, standard buffer solutions are employed to calibrate the pH meter.

BOD DETERMINATION

Biochemical oxygen demand (BOD) is a measure of the dissolved oxygen consumed by microorganisms during the aerobic breakdown of organic matter in water. BOD analysis helps estimate the level of biodegradable organic matter in wastewater, effluent, and polluted waters. The two commonly used methods for BOD measurement are the dilution method and the manometric method.

Dilution method: In this standard approach, the sample (dilution water) is prepared by adding inorganic nutrients, buffer salts, and enough bacteria to purified water. Several dilution levels of the sample are then created. BOD bottles are filled, capped, sealed, and incubated in the dark at 20 °C for 5 days. The dissolved oxygen levels are measured before and after the 5-day incubation period. The BOD5 value is calculated as the difference between these two values, corrected for dilution and the blank.

Manometric method: This method involves fitting a manometer into an undiluted sample bottle. The manometer continuously monitors the air pressure drop inside the bottle, reflecting the amount of oxygen uptake by the sample. Compared to the dilution method, the manometric method is simpler, as it does not require dilution, and allows for continuous measurements.

COD DETERMINATION

Chemical oxygen demand (COD) refers to the assessment of oxygen needed for the chemical oxidation of organic substances in water, making it a crucial indicator of water and wastewater quality.

The COD test involves adding a strong oxidant to the sample under acidic conditions. After the oxidation process is complete, the remaining oxidant in the solution is determined by titration using an indicator solution. Unlike the BOD test that takes several days, the COD test is relatively faster, usually taking 2-3 hours. It measures all organic contaminants, including non-biodegradable organics.

COD can be analyzed using a cuvette pre-filled with reagents containing chromium (VI). During thermal pre-treatment, the organic contaminants of the sample convert chromium (VI) to chromium (III). The amount of consumed chromium (VI) is directly proportional to the COD, and it can be detected through photometry.

NP ANALYZERS

Soil nutrients like nitrogen (N) and phosphorus (P) play a vital role in supporting plant growth. However, an excessive deposition of nitrogen can harm the soil ecosystem by increasing soil acidity, causing nutrient imbalances, altering soil microbe composition, and contributing to higher greenhouse gas emissions. For this reason, it is crucial to regularly test for nitrogen in food and environmental laboratories.

Various methods are available for determining nitrogen content. These methods involve an initial oxidation step that converts nitrogen-containing organic compounds into inorganic nitrogen entities. The oxidation step can be carried out using methods such as Kjeldahl digestion, ultraviolet (UV) oxidation, persulfate oxidation, or high-temperature oxidation (combustion).

Measuring phosphorus has become a critical aspect of environmental analysis. Elevated levels of phosphorus and nitrogen in water bodies can negatively impact water quality, leading to rapid toxic algae growth. Phosphorus analysis is typically performed using the ascorbic acid-molybdate method, often using a ready-to-use test kit that is quantitatively analyzed by a photometer. N and P analyzers can be individual instruments or a combination of both analyzers.

TOC ANALYSIS

Total organic carbon (TOC) quantifies the carbon content in organic compounds and is a highly sensitive, non-specific measurement of all organic matter present in a sample. It finds application in regulating the discharge of organic chemicals into the environment from manufacturing plants. In the field of potable water purification, detecting TOC is crucial due to its association with disinfection byproducts. TOC determination can be achieved through various approaches:

1. Off-line measurements involve collecting water samples in containers and transporting them to the instrument for analysis.
2. On-line measurements connect the instrument directly to the purified water stream.
3. TOC determination involves the oxidation of organic molecules.
4. Instruments designed to selectively detect CO2 are used for measuring TOC.

This method is often viewed as a complementary approach to COD and can also be performed using specific cell test kits.

DISSOLUTION / DIGESTION

Sample preparation is a crucial step in the analytical process, as samples often require treatment before direct analysis. The goal is to convert the analyte into a uniformly dissolved form. Since the quantity of reagents used in sample preparation is typically higher than the sample itself, it is essential to use reagents with appropriate purity to prevent sample contamination or false positive results. Sample preparation involves various techniques, such as dissolution, digestion, melting, and extraction, among others. In inorganic analysis, digestion is commonly employed to convert hardly soluble samples into a liquid form for easy analysis. Digestion agents like acids, caustic alkalis, bases, and salts are utilized and must be of good quality to avoid sample contamination.

GRAVIMETRIC ANALYSIS

Gravimetric analysis is an analytical chemistry technique used for the quantitative determination of an analyte based on its mass. Various types of this analysis method include precipitation, volatilization, and electro-analytical methods. Gravimetric analysis requires several inorganic reagents to facilitate the desired reaction with the analyte.