Climate monitoring and ultrapure water

About a few decades ago, Carlo Barbante of the University of Venice's School of Environmental Sciences and his research team began digging up the snow in Antarctica for trace analysis of heavy metals. These deep frozen snow can record atmospheric conditions for centuries, and the amount of heavy metals can show how air pollution conditions change over time.

Professor Carlo Barbante of the University of Venice is very interested in how the air pollution situation has changed, especially in the past. Because snow can absorb pollutants such as heavy metals in the air, and the snow in Antarctica has been frozen for centuries, it can provide historical information about the past. Heavy metals such as calcium, lead, zinc, and copper are very low in snow; today's snow in Greenland contains hundreds of grams of heavy metals per gram, and is taken from the New Era of Antarctica (about 50,000 years ago). The snow contains tens of grams per gram. Because of the extremely low content, the purity of the sample to be tested is very important. The team's most recent expedition was to COAT land in Antarctica, where they collected samples from 1915 to 1985 for seventy years.

Sampling

Taking samples from the snow in the Antarctic, first remove some sources of pollution, including removing the jewelry and glasses worn by the operator, and then digging a sample pit 8.3 meters deep to sample. The operator should dig and sample the stainless steel tool with acid treatment. Wear clean overalls and take 40cm x 30cm x 33cm sample blocks in the pit wall of the sample pit. Each piece can be drawn for about two years. The state of the atmosphere. To rule out metal contamination from any other source, the sample block was scraped into an acid treated double polyethylene bag with an acid treated polyethylene spatula. After the sample is processed, it is stored in a freezer at -10 ° C and then shipped back to the laboratory by ship.

In the laboratory, the sample block was subsampled according to the designed procedure, and representative samples were taken as much as possible. The subsampling was carried out in a 15 ° C cold room with an ultra-static stage designed specifically for laminar flow. The ultra static table and other instruments are made of the acid treated polyethylene previously used. The second sample was placed in a polyethylene bottle, acidified with nitric acid, and stored frozen.

2. Sample preparation and analysis

In the trace analysis of the sample, two factors are particularly important: 1. to ensure that the sample is not contaminated; 2. the accuracy of the test. The University of Venice has established a very clean laboratory for trace analysis studies. Even high-efficiency particulate filters and air exhaust fans are made from low-concentration polyethylene.

Early work has provided researchers with enough confidence that ICP-MS can be used to analyze samples as long as the sample can be concentrated thirty times by evaporation. The concentration of the sample will obviously concentrate the contaminants in the sample, but the concentration process is also likely to bring in new sources of contamination. Therefore, researchers are eager to find a way to directly analyze samples without any concentration treatment.

They chose ThermoFinnigan's ICP-SFMS with a PFA-100 microfluidizer (nebuliser) and attached to a polyfluoroacetic acid dual channel spray chamber maintained at room temperature. The thawed sample was drawn from the vial through a PFA capillary using a Spetec peristaltic pump with a polyethylene tube. The system is pre-cleaned to minimize contamination and then treated with ultrapure nitric acid (1% pure aqueous nitrate) for at least 20 hours. The indicator they used was lead 208Pb, which was considered clean when the instrument's count stabilized at not less than 400 per second. The accuracy of instruments such as ICP-SFMS relies primarily on the purity of the blanks and standards used for proofreading and the double-distilled nitric acid used to clean the operating system and acidify samples with a lead content of 0.13 pg/g.

The parameters of the ICP-SFMS per day were optimized to offset the ultrapure nitric acidified 1.0 ng/g indium solution in order to obtain maximum signal response and stability. The ICP-SFMS was calibrated to offset a 100 μg/g multi-element standard solution from Merck that was diluted with ultrapure water for use as a blank.

3. Ultra pure water treatment

Giulio Cozzi is an expert in ultrapure water at the University of Venice, with a special focus on detail. He chose ELGA's Analytic Ultrapure Water Meter for his spectroscopy.

PURELAB Ultra Analytic is designed to purify purified water that has been pretreated. At the University of Venice laboratory, the equipment was used to purify pure water that had been subjected to reverse osmosis and had a resistivity of 0.1 MΩ.cm. The purified water is passed through a pre-purification column which removes all ionic and organic impurities using a mixed bed of ion exchange resin and an organic adsorbent. The heat source is then removed by external illumination by a low pressure mercury lamp capable of producing ultraviolet light at 185 nm and 254 nm. The longer the wavelength, the better the bactericidal effect of the ray, while the short-wavelength ray produces a free hydroxyl group, and traces of these photo-oxidized organic matter form charged ions. The second purified column is to remove ions produced by photooxidation and traces of ions remaining after primary purification, mainly sodium ions which are relatively high in drinking water. Resistivity monitoring between the two purification columns, the main purpose is to find the service life of the primary purification column in time, but the secondary purification column still maintains the ability to purify and purify, so even if the primary purification column has reached the end of its life, the refined water is treated. The quality will still not drop. The water treated by the secondary purification column is microfiltered through a 0.05 μm membrane and then recycled to the primary purification column, which is available when needed.

The quality of water is the key to successful operation, and the resistivity monitoring of water quality has been confirmed by an article published in the IET in May and June 2006.

The work of the University of Venice also proves that ultra-pure sampling and sample preparation according to the procedure, together with the ultra-pure water of stable quality, can carry out trace analysis of heavy metals without concentration. Veolia's ELGA Purified Water Department, which specializes in laboratory water, is happy to assist in the analysis of trace elements in Europe to provide ultrapure water.

4. Performance indicators of ultrapure water

The resistivity of ultrapure water is an easy-to-measure indicator that shows whether the purification system works properly, but it is especially important for the Giulio Cozzi research team to find out what pollutants are in the ultrapure water in their daily research. of. Therefore, whenever the sample analysis of snow is performed, the analysis of ultrapure water is first performed.

TABLE 1 – Trace Element Analysis of Water from Ultra Analytic

The content of impurities in the ultrapure water sample has reached the level of purity of the blank, and the low content of these impurities in the ultrapure water can be stably maintained.

5. Results

The sample from the outermost 2 cm of the sample block was compared with the sample from the inside, and the heavy metal content in the outer layer was found to be particularly high, which indicates that the sample surface is contaminated, and it also indicates how difficult it is to obtain a sample that is completely free from environmental pollution. For this reason, only samples derived from the central portion of the sample block were analyzed.

Samples from different depths have different levels of heavy metals, which allows researchers to discover patterns of heavy metals entering Antarctica. This is often associated with long-distance transmission of crustal dust from arid regions such as South America, South Africa, and Australia. Other modes of entry include volcanic eruptions that cause radiation dust.