**1.1 Fundamentals**

The spectra of atomic absorption of an element are made up of a series of lines of resonance from the fundamental state to different excited states. The transition between the fundamental state and the first excited state is known as the first line of resonance, being that of greatest absorption, and is the one used for analysis.

The wavelength of the first line of resonance of all metals and some metaloids is greater tan 200 nm, while for most non-metals it is lower than 185 nm. The analysis for these cases requires modifications of the optical systems which increases the cost of atomic absorption instruments.

In atomic absorption spectrometry, no ordinary monochromator can give such a narrow band of radiation as the width of the peak of the line of atomic absorption. In these conditions the Beer Law is not followed and the sensitivity of the method is reduced. Walsh demonstrated that a hollow-cathode, made of the same material as the analyte, emits narrower lines than the corresponding lines of atomic absorption of the atoms of the analyte in flame, this being the base of the instruments of atomic absorption. The main disadvantage is the need for a different lamp source for each element to be analysed, but no alternative to this procedure improves the results obtained with individual lamps.

The energy source most frequently used in atomic absorption spectroscopy is the hollowcathode lamp.

## **1.2 Types**

4 Macro to Nano Spectroscopy

A = abc when b (trajectory of the radiation) is expressed in cm and c (concentration of the substance)

A = εbc when b is expressed in cm and c in mol.L-1, a (absorptivity) is called molar absorptivity and

The absorption of light (A) = log Po/P ( = Optical density or extinction)

The Bouger-Lambert-Beer Law is fulfilled with limitations in molecular absorption

In 1927, Werner Heisenberg proposed the principle of uncertainty, which has important and widespread implications for instrumental analysis. It is deduced from the principle of superposition, which establishes that, when two or more waves cross the same region of space, a displacement is produced equal to the sum of the displacements caused by the individual waves. This is applied to electromagnetic waves in which the displacements are the consequence of an electric field, as well as to various other types of waves in which atoms or molecules are displaced. The equation ∆t x ∆E = h, expresses the uncertainty principle, signifying that, for finite periods, the measurement of the energy of a particle or system of particles (photons, electrons, neutrons, protons) will never be more precise than h/∆t, in which h is the Planck´s constant. For this reason, the energy of a particle may be known as a zero uncertainty only if it is observed for an infinite period (Skoog et al., 2001). In 1953, the Australian Physicist Alan Walsh laid the foundations and demonstrated that atomic absorption spectrophotometry could be used as a procedure of analysis in the laboratory (Willard et al., 1991). The theoretical background on which most of the work in

this field was based is due almost entirely to this author (Elwell & Gidley, 1966).

that of greatest absorption, and is the one used for analysis.

The spectra of atomic absorption of an element are made up of a series of lines of resonance from the fundamental state to different excited states. The transition between the fundamental state and the first excited state is known as the first line of resonance, being

The wavelength of the first line of resonance of all metals and some metaloids is greater tan 200 nm, while for most non-metals it is lower than 185 nm. The analysis for these cases requires modifications of the optical systems which increases the cost of atomic absorption

According to the Bouguer-Lambert-Beer Law:

where:

Po: Incident radiation P: Transmitted radiation

**1.1 Fundamentals** 

instruments.

in g.L-1, the units of a (absorptivity) are L.g-1.cm-1, or

it is represented by the symbol ε and its units are L.mol-1.cm-1

Absorptivity, a, is A/bc (= Coefficient of extinction)

spectrophotometry (Skoog et al., 2008).

Molar absorptivity, ε, is A/bc (= Coefficient of molar extinction)

The field of atomic absorption spectroscopy (AAS) includes: flame (FAAS) and electrothermal (EAAS or ETAAS) atomic absorption spectroscopy (Skoog et al., 2008). The base is the same in both cases: the energy put into the free atoms of the analyte makes its electrons change from their fundamental state to the excited state, the resulting absorbed radiation being detected. However the fundamental characteristic of the FAAS is the stage of atomization which is performed in the flame and which converts the analyte into free atoms, whereas in the EAAS the stage of atomization goes through successive phases of drying, calcination and carbonization, and it is not required to dissolve the sample in the convenient matrix as occurs with the FAAS (Skoog et al., 2008; Vercruysse, 1984).

#### **1.2.1 Flame atomic absorption spectroscopy**

Prior steps to the stage of atomization in flame are the treatment of the sample, dissolving it in a convenient matrix, and the stage of pneumatic nebulisation. In FAAS the stage of atomization is performed in flame. The temperature of the flame is determined by the fuel/oxidant coefficient. The optimum temperatures depend on the excitation and ionization potentials of the analyte.

The concentration of excited and non-excited atoms in the flame is determined by the fuel/oxidant coefficient and varies in the different regions of the flame (Willard et al., 1991).

#### **1.2.2 Electrothermal atomic absorption spectroscopy**

The electrothermal atomic absorption spectrophotometer has three part: the atomizing head, the power source and the controls for feeding in the inert gas. The atomizing head replaces the nebulising-burning part of the FAAS. The power source supplies the work current at the correct voltage of the atomizing head. The computer control of the atomizing chamber ensures reproducibility in the heating conditions, establishing a suitable profile of temperatures in the heating scale from environmental temperature to that of atomization so that the successive stages of drying, calcination and carbonization the sample must go through are those required. The working temperature and the duration of each stage of the electrothermal process must be carefully selected taking into account the nature of the analyte and the composition of the matrix of the sample. The control unit which measures and controls the flow of an inert gas within the atomizing head is designed to avoid the destruction of the graphite at high temperatures due to oxidation with the air.

Atomic Absorption Spectroscopy: Fundamentals and Applications in Medicine 7

The disintegration of uranium and plutonium atoms in atomic explosions provokes the appearance of a series of elements with maxima in atomic weight of around 90 and 140. The isotopes of heavier atomic weight (140) fall in the area of the explosion while those of lower atomic weight (90) enter the troposphere and stratosphere. The particles which enter the troposphere spread out forming a gigantic belt around the area and are later deposited in local rain. Those others which reach the higher zones – the stratosphere – can be

Atmospheric and tropospheric precipitation follow more or less quickly but the contaminants in the stratosphere may take many years before falling into the troposphere

Among the elements thrown into the troposphere and stratosphere are found those of the first peak of atomic weight (about 90), with two of the artificial isotopes of Sr, 89Sr and 90Sr,

The Sr deposited by the rain together with the Sr present in nature is absorbed by plants through the roots and that which is deposited on the leaves may also be absorbed. From here it enters the human organism, either directly by consuming the plants or, indirectly, by

Once the Sr has entered the organism it is carried in the blood to the cartilage and bone,

In face of this threat, the analyses of animal milk for human consumption as markers of radioactive contamination and strategies to prevent the uptake (intestinal absorption) or to facilitate the elimination of 90Sr from the bone once it has bonded are priority research into

**2.1.2.1 A curiosity in biological barriers: discrimination between strontium and calcium**  It is assumed axiomatically that biological organisms use Sr less effectively than Ca, which means that they discriminate against Sr in favour of Ca. This may be expressed in another manner by the concept "Strontium-Calcium Observed Ratio" (OR), the value of which is lower than 1. Comar et al. (1956) introduced the term to denote the overall discrimination observed in the movement of the two elements from one phase to another under steadystate conditions. The term OR denotes the comparative rates of Sr and Ca in balance

OR= (Sr/Ca) sample/(Sr/Ca) precursor. More precisely, the OR can be defined as the product of a number of 'discrimination factors' (DF), each of which is a measure of the extent to which the physiological process to which it

In this line it is shown one of the first studies which aimed to ascertain at what intestinal level the Sr/Ca discrimination takes place. Vitamin D3, 25-hydroxy-cholecalciferol (25-0H-CC) and 1,25-dihydroxy-cholecalciferol (1,25 (OH)2-CC) were administered to rats. The apparent and

with different half lives. In particular, the half life of 90Sr is 28.79 years.

choice sites for bonding. Far lower rates are found in other tissues.

between a sample and its precursor and is defined as:

refers contributes to the overall discrimination.

**2.1.1 Introduction** 

disseminated in over wide areas.

and being deposited in zones of greater rainfall.

eating the animals which have eaten them.

Sr domain (Escanero, 1974).

**2.1.2 Development** 

One variant of the graphite oven is the carbon bar atomizer.

The main advantages of electrothermal atomic absorption are:

