Fundamentals Of Environmental Sampling And Analysis Pdf


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Fundamentals Of Environmental Sampling And Analysis Pdf

Three of the more common classical open tubed acid digestion procedures were explored with the purpose of optimizing the variables and selecting the single most efficient, convenient and inexpensive digestion method. The effect of parameters such as digestion media, digestion time and digestion temperature on the efficiency of extraction of heavy metals from fish tissue was examined.

Concentrated nitric acid was determined to be the most efficient digestion media for all the metals studied. This procedure describes a low cost open digestion method.

The main advantages of this method are superior extraction efficiency, speed, ability to analyze multiple elements including volatile elements, ability to digest large volumes of samples and reduced cost. Many researchers use microwave digestion techniques to solubilize biological samples [1] , [2] , however, without such costly equipment available, open acid digestion presents the most viable option. There exists no single open acid digestion procedure for the analysis of metals for all biological materials [3].

The nature of the biological sample, the analyte, the reagent availability and equipment usually play a decisive role in the selection of the digestion procedure because it helps to select the best conditions suitable to give the highest yield of extractable metals. The selection of digestion reagents depends on the sample matrix and the metals being analyzed. Their oxidizing strength can be increased by the addition of chlorate, permanganate and hydrogen peroxide.

Nitric acid is the most commonly used acid for oxidation of organic matrices. Its oxidizing strength can be increased when used in conjunction with other acids. Although hydrochloric acid is a non-oxidizing acid when used alone, when mixed with nitric acid aqua regia in a certain proportion HCl:HNO 3 ratio , it becomes a strong oxidizing agent. This is because the products of their reaction, nitrosyl chloride and chlorine are strong oxidizing agents [3].

Some metals form insoluble precipitates with the anion of the acid therefore some acids are totally incompatible with certain metals [4]. The digestion efficiency can also be influenced by other factors such as temperature and digestion time.

The digestion temperatures of open acid digestion systems are determined by the boiling points of the acids and the volatility of the analyte [5]. Temperature increases the average kinetic energy resulting in increased collisions between the acid and biological sample which enhances the dissolution of metals [6].

However, when heat is applied to the vessel containing the solution it usually takes time for the solution to begin to heat up.

The digestion process is also limited by the boiling point of the acid or acids used. In multi-acid digestion, the most volatile acids boil away first followed by the next most volatile [7]. High temperatures, in excess of the boiling point of the acid or acid mixture, can result in a loss of volatile metals such as mercury and lead [6].

Digestion time is another important factor because it controls the length of exposure of the matrix to the oxidizing acid. The length of exposure can increase exothermic processes which will increase the extent of solubilization of the metal of interest from the biological matrix as well as the loss of these metals through volatilization [8]. Therefore, it is important to ensure that the most efficient digestion temperature and time is selected to obtain the best recovery of the element.

A simple, efficient and cost effective method had to be adopted because a large quantity of fish muscles samples needed to be analyzed hence the purpose of this study were to optimize the extraction of a range of metals by:.

Obtaining the most efficient and cost-effective combination of digestion media, digestion time and digestion temperature that would completely extract all the metals of interest. The homogenized tissue was subsampled and 0. Samples were then cooled and filtered through Whatman No. Additional treatment steps were required for arsenic, antimony, selenium and mercury following digestion. Mercury had to be reduced to the ground state atoms while arsenic, antimony and selenium had to be converted to the respective hydrides before analysis.

The acid blank digests and spiked samples were processed in a similar manner. See Fig. Flowchart outlining pre-reduction and stabilization steps between acid digestion and sample analysis. The specific atomic absorption spectrophotometry technique and the corresponding conditions used to achieve the best analytical sensitivity and precision for each metal is shown in Table 2.

The reducing agents, stannous chloride and sodium borohydride were prepared daily. Since arsenic, antimony, mercury and selenium were both being determined on the same sample, mercury and selenium were determined first to avoid cross-contamination from the potassium iodide used in the reduction process for Antimony and Arsenic.

Potassium iodide has the potential to suppress the analytical signal for these metals [10]. In order to evaluate the accuracy of the acid digestion method 0. The results obtained were compared with certified results, and recoveries determined. In addition to the use of a Certified Reference Material, spiked sample recoveries were also determined for each metal. The recoveries were determined. Heavy metal analysis of biological material requires the metals to be completely solubilized from the matrix through acid digestion.

This is one of the most labor intensive and time consuming steps of the procedure. The suitable optimized conditions for each variable digestion media, temperature and time were selected for each metal being analyzed. Due to the large number of fish samples to be analyzed the optimized conditions that gave the best metal recoveries and could be applied to the widest range of metals was desirable.

Such a procedure would reduce analysis time as well as the quantity of chemicals to be used, which lowers risks and ensures cost effectiveness.

The experiment was conducted using three acid combinations while varying the digestion temperatures and times. The optimized acid for digestion of all the metals was nitric acid as shown in Fig. From the data obtained and the graphical displays of Fig. This finding was supported by research done by [15] which suggested Nitric Acid as the most efficient digestion agent for fish muscle tissue. The digested samples were clear and transparent which indicated there was complete digestion of the sample and therefore release of the bound heavy metals from the sample matrix.

These are summarized in Table 3. This occurs when metals adhere to the surface of the vessel and does not reach the atomizer to be atomized [10]. To prevent this from occurring a longer delay time is recommended to allow all the metal to enter the atomizer. In addition, flushing the tubing with deionized water between consecutive samples could further prevent memory effects. This is generally in keeping with the theory that acid digestions will yield the highest recovery at the boiling point of the acid.

The extent of dissolution of the metals were possibly enhanced by the prolonged exposure of the sample to nitric acid. Arsenic and antimony behaved quite similarly because they both exist in the same oxidation state and yielded good recoveries in a shorter space of time compared to the other metals. A spiked recovery analysis was performed as an additional form of quality control to calculate the recovery of the analyte spike added to the sample prior to sample preparation Table 3.

It was used to determine any matrix effects and sample preparation losses [3]. This study proves that efficient digestion of fish tissue can be achieved with minimal losses using simple controlled open acid digestions. National Center for Biotechnology Information , U. Journal List MethodsX v. Published online Nov Author information Article notes Copyright and License information Disclaimer. Elisabeth Mohammed: moc. Received Feb 3; Accepted Nov 3. This article has been cited by other articles in PMC.

Graphical abstract. Open in a separate window. Method name: Acid digestion of fish tissue. Keywords: Heavy Metals, Digestion, Optimization. Method details This procedure describes a low cost open digestion method. The variables to be optimized include: 1. Table 1 Variables acid, temperature and time optimized for acid digestion. Discussion Heavy metal analysis of biological material requires the metals to be completely solubilized from the matrix through acid digestion.

Table 3 A summary of the acid digestion optimized conditions selected. References 1. Determination of heavy metals in fish samples of the Middle Black Sea Turkey by graphite furnace atomic absorption spectrometry. Food Chem. Uluozlu O. Trace metal content in nine species of fish from the Black and Aegean Seas, Turkey. Xiao Jing. Brock University; MSc Diss. Zhang C. Wiley Piblishing; Fundamentals of Environmental Sampling and Analysis. Robinson J. CRC Press; Undergraduate Instrumental Analysis.

Theory of sample preparation using acid digestion, pressure digestion and microwave digestion microwave decomposition. Kingston H. Comparison of microwave versus convention dissolution for environmental applications. Gavriloaiei T. Considerations of microwave- assisted digestion: towards a conceptual model; pp.

Analele Stiintifice De Universitatii A. Cuza Din Iasi.

Fundamentals of Environmental Sampling and Analysis

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Analytical chemistry

Analytical chemistry studies and uses instruments and methods used to separate , identify, and quantify matter. Separation isolates analytes. Qualitative analysis identifies analytes, while quantitative analysis determines the numerical amount or concentration. Analytical chemistry consists of classical, wet chemical methods and modern, instrumental methods.

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Comprehensive Sampling and Sample Preparation is a complete treatment of the theory and methodology of sampling in all physical phases and the theory of sample preparation for all major extraction techniques.

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