AHMAD RAZALI BIN ISHAKDEPARTMENT OF ENVIRONMENTAL HEALTHFACULTY OF HEALTH SCIENCESUITM PUNCAK ALAM

Sample Preparation for inorganic trace analysis

Lecture 2

Solid Samples

Introduction

Analysis for metals in solids-2 different approach

1. Direct analysis of solid-X-ray florescence (self study-assignment)

2. After decomposition

Decomposition techniques

involves liberation of analyte (metal) of interest from interfering matrix

Using a reagent (mineral/oxidizing acids or fusion or flux) And/or Heat

Problem- risk of contamination and loss of analytes

Dry ashing

The simplest of all decomposition systems involves the heating of the samples in porcelain crucible in a muffle furnace in the presence of air at 400-800C

After decomposition, the residue is dissolved in acid and transferred to a volumetric flask prior to analysis.

Allow organic matter to be destroyed.May lead to the loss of volatile elements (Hg,

Cd, Ca, As, Sb, Cr and Cu)

Cont..

Disadvantages of this method: Loss due to volatilization Resistance to ashing by some materials Difficult dissolution of ashed materials High risk of contamination

It has largely been replace by wet ashing

Wet digestion (Acid digestion)

The use of mineral or oxidizing acids and an external heat sources to decompose the sample matrix.

The choice of an individual acids is dependent upon the nature of the matrix to be decomposed

Once the choice of acid is made the sample is placed into an appropriate vessel for decomposition stage

Vessel- carried out in open glass vessels(beakers or boiling tubes) using hotplate (in FSK) or multiple sample digester

The US EPA method for acid digestion of sediments, sludges and soils are outlined in figure 1

Figure 1

The digestion of food stuffs can be carried out in a similar manner

A typical procedure for digestion of foodstuffs e.g. cereals, meats, fish and vegetable for determination of total metal content (cadmium,cooper,iron, lead and zinc) in figure 2

Figure 2

Microwave digestion

An alternative approach to conventional heating involves the use of microwave heating

Advances in technology by a variety of manufacturers means that today there are two types of microwave heating systems commercially available : open-focused and closed vessel system.

closed vessel system

Liquids-Natural and waste waters

Introduction

Analysis of liquid samples for metals-required no sample pre-treatment-just a simple filtration (0.2 um)of the sample to remove particulates prior to introduction into chosen instrument.

However, reality is often very different and even most sensitive of analytical technique (e.g. ICP-MS) may require some additional sample pre-treatment; separation or pre-concentration

Pretreatment/pre-concentration-potential contamination-great care required

Liquid-liquid extraction

Addition of a suitable chelating agent to the water samples to form metal complex

Will effectively partition into an immiscible organic solvent

Metal present in a large volume of sample water is effectively and quantitatively transferred into a small volume of organic solvent.

The important variables in LLE are as follows:

a) Choice of chelating agentb) Choice of organic solventc) pH of the aqueous sampleThe most commonly used chelating agent in

AAS is Ammonium pyrrolidine dithiocarbamate (APDC). This reagent can be directly extracted with methyl isobutyl ketone (MIBK) as the organic solvent.

Typical procedure LLE of metals

AHMAD RAZALI BIN ISHAKDEPARTMENT OF ENVIRONMENTAL HEALTHFACULTY OF HEALTH SCIENCESUITM PUNCAK ALAM

Sample preparation for organic analysis

Lecture 3

Solid Samples

Introduction

New instrumental approaches-led to development -speed of extraction, reduction in organic solvent consumption and introduction of automation.

However, this instrumental approaches-higher price tag than the conventional.

Extraction of env. Pollutant from solid or semi solid matrices can be divided into several categories based on the method of extraction, mode of heating, and presence or not of some type of agitation.

Various method of extraction of analyte from solid matrices

Types of extraction-Solid

Soxhlet extractionShake flask extractionUltrasonic extractionSupercritical Fluid Extraction (SFE)Microwave assisted extractionPressurized Fluid ExtractionMatrix solid phase dispersion

Soxhlet Extraction

The basis of soxhlet extraction apparatus consist of a solvent reservoir, and extraction body, a heat sources (e.g. isomantle) and a water-cooled reflux condenser

A soxhlet uses a range of organic solvent to remove organic compounds, primarily from solid matrices

The solid sample (e.g. 10 g soil) and a similar mass of anhydrous sodium sulfate are placed in the porous thimble (cellulose) which in turn is located in the inner tube of Soxhlet apparatus

The apparatus is then fitted to a round- bottom flask of appropriate volume containing organic solvent of choice and to reflux condenser.

The solvent is then boiled gently-The solvent vapor passes up through the tube is condensed by the reflux condenser and the condensed solvent falls into the thimble and slowly fills the body of soxhlet apparatus

When the solvent reaches the top of the tube, it syphons over into the round-bottomed flask the organic solvent containing the analyte extracted from the sample in the thimble. This solvent is then said to have completed one cycle.

The whole process is repeated frequently until the pre-set extraction time is reached.

As the extracted analyte will normally have higher boiling point than the solvent, it is preferentially retained in the flask and fresh solvent re-circulates

Typical procedure for Soxhlet extraction

Shake Flask Extraction

Conventional LLE in the form of shake flask extraction is carried out by placing samples (e.g. soil) into a suitable glass container, adding a suitable organic solvent and the agitating or shaking

Typical procedure used for shake flask extraction

Ultrasonic extraction

Sonication involves the use of sound waves to agitate a sample immersed in an organic solvent-using sonic probe or sonic bath

The sample is placed in suitable glass container and enough organic solvent is then added to cover the sample.

The system is then sonicated for a short period typically 3 min using sonic bath or probe

After extraction, the solvent containing the analyte is separated by centrifugation and/or filtration and fresh solvent added.

The whole process is repeated three times and all of the solvent extract are then combined.

Typical procedure for ultrasonic extraction

Cont..

Liquid Samples

Types of extraction-Liquid

Liquid Liquid extraction (LLE)Solid phase extraction (SPE)Solid Phase Microextraction (SPME)

Liquid-Liquid Extraction

The sample is distributed/partitioned into two immiscible solvent which analyte and matrix have different solubility

Advantage-wide availability of pure solvent, low cost apparatus

Typical procedure for LLE

Solid phase extraction

Liquid-solid extractionBringing a liquid sample into contact with a

solid sorbent whereby the analyte is selectively adsorbed onto the surface of solid phase.

The latter is then separated from solution and other solvents are added.

Solid Phase extraction

The first solvent-wash to remove possible contaminant

Then, Liquid sample bring into contact with a solid phase/sorbent whereby analyte is selectively adsorbed onto the surface of solid phase.

The analyte then separated from the solid phase by eluting solvent.

This solvent is then collected for analysis.

Typical procedure for SPE

Solid Phase Micro Extraction (SPME)

The process whereby an analyte is adsorbed onto the surface of a coated silica fiber as a method of concentration.

This is follow by desorption of the analyte into a suitable instrument for separation and quantification

Volatile Compounds

Introduction

Volatile compounds in the atmosphere, workplace and on industrial sites need to be monitored with regard to safety consideration

This VOC, can be trapped either on a solid support material (for thermal desorption) or liberated from water sample and then trapped (e.g. via purge and trap) prior to analysis.

Self study

Thermal desorptionPurge-and-trap

Thank You