PRECIO ESTIMADO DE LA RED WiMAX Wi-Fi A SER

10.0 Introduction

The overall aim o f this European Union project is to develop a quantitative

Aquatic Passive Sampler (APS) that will measure time-integrated concentrations of

pollutants in environmental waters.* In turn, the motivation for this individual Ph.D.

thesis was brought about by the need to investigate and understand the physico­

chemical interactions involved in the retention of pollutants on a Cig solid-phase

extraction (SPE) disk, which has been completed successfully in Chapters 7, 8 and 9.

The disk consists of a PTFE microfibril network embedded with silica-bonded

octadecyl sorbent phase and is taken as the receiving phase in the European Union’s

Aquatic Passive Sampler, which is described in full in Chapter 3. In Chapter 7, it is

shown how the equilibrium constant (Keq) and the uptake rate constant (kup) for the

partitioning of pollutants between water and the Cig SPE disk in a closed system can

be determined by experiment. The findings in Chapter 7 as well as Chapters 8 and 9

show that a novel experimental procedure utilising on-line ultra-violet (UV)

spectroscopy, is a viable method for studying the thermodynamic and kinetic

partitioning of compounds between these two condensed phases.

The successful characterisation of the water-Cig SPE disk system (Chapter 9)

enables one to predict log K@q for the retention o f any compound on the receiving

phase provided the Abraham solute descriptors are known. It is therefore of particular

importance to ascertain if the log Keq values obtained for compounds partitioning

between the water-naked Cig disk system are applicable to a water-APS system too. In

the Aquatic Passive Sampler a rate-limiting membrane (R-LM) forms a physical

barrier between the water and the receiving phase in an attempt to control the rate of

diffusion of pollutants to the surface of the receiving phase/ It is expected that the R-

LM will not ^ffect the physico-chemical interactions involved in retention of

V pollutants onto the Cig disk but may well fe^fect the uptake rate constant, log kup. In

addition to this it is essential to determine if the physical constants determined for a

‘closed’ water-Ci8 disk or -APS system are applicable to an ‘open’ water-Cig disk or -

APS system. The reason being that the APS’s intended use is to monitor time-

integrated pollutant concentrations in environmental waters such as lakes, rivers etc.

These are denoted as ‘open’ systems and are different to the ‘closed’ system used to

obtain Keq and kup in this work. To ensure clarity between the two, ‘closed’ and ‘open’

partitioning systems in this work are defined as follows:

Closed system - water (Vw) and receiving phase ( Vd) volumes are known.

The concentration of pollutant in water ([A]w) decreases

with time as it partitions into the disk / APS.

Open system - receiving phase volume is known but volume of water is

unknown or infinitely large compared to Vq. The

concentration of pollutant in water is constant with time.

!

In this chapter several preliminary experiments are carried out to obtain^ log K^q and

log kup by the UV spectroscopy method detailed in Chapter 7.5 for the partitioning of

diuron between water and the APS. The constants obtained are viewed along side

those for a ‘closed’ water-Cig disk system (from Chapter 7) as well as additional

determine the concentration of diuron in water and the receiving phase during various

partition experiments in both closed and open water-APS systems.^ The R-LM used

for these C3q)eriments is the polysulphone membrane selected for the time-integrated

measurement of relatively polar pollutants by J. Kingston.^ The receiving phase is a

Cl8 sohd-phase extraction disk used in experimental work throughout this thesis. The

idea of the preliminary experiments is to obtain an indication of the values of log Keq

and log kup for a water-APS system and not to quantitatively determine these two

constants. This would be the type of work to be carried out in the future.

10.1 Calculating the Equilibrium Constant

Keq for a closed system (partitioning is followed by recording the change of

pollutant concentration in the waterl is calculated in exactly the same way as

previously defined by equation 7.2:

K e q = [ A ] o e q / [ A ] w e q = X [ A ] w ° ” [ A ] w e q ) / [ A ] w e q (7.2)

Where [ A J o e q and [ A ] w e q are the concentration of pollutant in the disk and the water at

equilibrium respectively, [ A ] w ° is the initial concentration in the water (all in mo 1.1'^)

an d /is the phase ratio (f= VwA^d where Vd and Vw are the volumes of the disk and

water respectively (litres)). For the sake of completion, Keq in an open system is

simply given as (where the change of concentration in the disk is usually recorded

when following the partition process):

K e q = [ A J o e q / [ A ] w e q (5.19)

[ A ] w e q is constant throughout the whole experiment and [ A ] o e q can be determined

directly by various analytical techniques, GC-MS in Kingston’s case.

10.2 Calculating the Uptake Rate Constant

kup is determined by fitting the partitioning data to equation 7.16 in the case of

absorbance data obtained by UV spectroscopy, to obtain constant c which in turn

gives kup from equation 7.17

Abs = sM + (Abs° - eM ) exp’*'"*’^ ^ (7.16)

Z K e q V D Z K e q V D

c = -kupZ (7.17)

where Abs° and Abs are the UV initial absorbance and absorbance at time t for the

pollutant in water. M is the total number of moles in the system, e is the extinction

coefficient for the pollutant under investigation and Z = 1 + Vw / Keq.Vo. In the case

of data collected by any other analytical technique, equation 7.15 is needed instead to

obtain constant c:

[A]w = M + ([A]w° - J y D e x p ^ ' (7.15)

ZKeqVo ZKeq Vo

It is worth pointing out that equation 7.15, 7.16 and 7.17 can not be used to determine

10.3 Results

10.3.1 Data obtained by Kingston

Experimental partition data obtained by Kingston that is comparable to that

obtained in the current work is described for the two scenarios below.^ Kingston uses

GC-MS to quantify either the concentration in water or the Cig disk.

Scenario 1: The concentration in water ([A]w in mo 1.1'*) is obtained for diuron

partitioning between a ‘closed’ water-APS system, 11°C, lOOOrpm.

Scenario 2: The concentration in the disk ([A]d in mo 1.1'*) is obtained for diuron

offloading from a pre-loaded disk, in an ‘open’ water-APS system,

11°C, slow stirring, over 15 days.^

10.3.2 Data obtained in the current work

Two separate experiments carried out in this work utilise the UV spectroscopy

procedure outlined in Chapter 10.7 Details are given below:

Scenario 3: The concentration in water ([A]w in moll'*) is obtained for diuron

partitioning between a ‘closed’ water-APS system, 23°C, 4G0rpm.

Scenario 4: The concentration in water ([A]w in mol.l'*) is obtained for diuron

partitioning between a ‘closed’ water-APS system, 23°C, 200rpm.

Log Keq and log kup for scenarios 1, 3 and 4 are given in Table 10.1. The offloading

rate constant log koff is obtained indirectly from log Keq and log kyp via equation 7.21

for scenarios 1,3 and 4.