Chemistry Reference
In-Depth Information
21.3.1
Blood and its extracts
Blood is a very complex bio-fluid consisting huge number of chemicals. Human blood contains erythrocytes
(red blood cells) and leukocytes (white blood cells) suspended in plasma. Several other bio-active structures
such as hormones, anti-bodies, dissolved proteins, glucose, mineral ions and also CO
2
and CO dissolved
gases exist in blood. Biochemical laboratories in which blood is analyzed use developed procedures including
quantitative determination of several indices such as sugar, total protein, bilirubin, creatinine, urea, uric acid,
several enzymes, lipid structures and dissolved cations. Any of the molecular indices in which concentration
level in blood falls in to the detection limit of IR spectroscopy could be proposed for quantitative assay. IR
spectrum of whole blood is full of interfering signals which are really hard to assign. In case of biomedical
analysis, blood spectrum is usually acquired by IR sampling techniques in which the quantification process
is performed. In this way, IR spectroscopic analyses are performed using fixed path-length accessories such
as attenuated total reflectance (ATR) or microspectrometry.
One of the most common applications of IR spectroscopy for whole blood analysis is in monitoring of
blood sugar. Diabetes is a very harmful metabolic disease. Medical concerning services report a wide range
of body organ damage such as renal failure, blindness, brain damage or heart attack related to diabetes. About
5
of US citizens have diabetes and usually they have no control system which inhibits the increment in
blood sugar content. Thus they need some medical treatment and also continuous monitoring of fast blood
sugar as an informative parameter in disease stage recognition. One of the primary methods for measurement
of glucose by IR spectroscopy was based on tissue penetration of IR ray which demonstrated some drawbacks.
There were also some assays using whole blood as the sample matrix but problems due to interference of
other constituents such as RBC gamma globulin and albumin lead to some limitations [8-10]. Later on and
by development of data processing utilities the interference problems were resolved and IR spectroscopy
could precisely monitor the whole blood glucose.
There are several reports indicating different sample physical states such as fresh blood, EDTA stabilized
blood or dried samples which can be analyzed as a film. On the other hand, diffuse reflectance, attenuated total
reflectance, photo acoustic and also transmission techniques have been applied for this aim [11-17]. Of course
in case of liquid samples the role of water (about 90
%
of blood) is very important. There is a problem in
mid-IR spectral region due to the intensive absorbance signals of water which restricts the extraction of useful
signals and behaves as a shield which covers most of the important spectra characteristics. The common idea
to avoid this problem is to use water's spectrum as the background. There is also a trend for development of
more precise, accurate and sensitive procedures based on mid-IR spectroscopy. Researchers investigating the
mid-IR spectroscopy for application in determining glucose in whole blood samples have reported a very
different spectral region or even a single wavenumber as the best characteristic for the data extraction and
analysis of signal-concentration correlation. The most indicted ones are 1200-950, 1500-750, 1119-1022,
1109, 1093, 1082 and 1040 cm
−1
[18-22]. Thus it seems very important to select the optimal spectral region or
signal by utilizing wavelength selection chemometric routes. Software supported elimination of spectral
interferences and selection of more powerful instrumental hardware will also provide more reliable results.
Some other constituents in whole blood samples have also been quantitatively and qualitatively analyzed by
means of mid-IR spectroscopy, for example; hematocrit, albumin, glycoproteins and fibrinogen [23-25].
Recently, the suggestion was made to use the whole blood sample's mid-IR spectra for disease pattern
recognition [26]. This idea will be discussed later in this chapter. It is a common pre-treatment procedure to
use ethylene diamine tetra acetic acid (EDTA) as anticoagulant agent prior to analyze the whole blood samples.
Plasma and serum are two major blood components which have been commonly applied in IR spectroscopic
studies as the analyzed sample. Plasma is a yellow liquid (more than 50
%
%
volume) in which blood cells are
suspended. Water makes up about 90
of plasma. Glucose, hormones, proteins, clotting factors, hormones,
dissolved ions and hormones are the main ingredients of plasma. The experimental procedure for preparation
%
