X-Ray Fluorescence in Biological Sciences. Группа авторов
development and function, and also interfere with the normal functioning of other bodily organs and systems. Exposure to Pb can pose a substantial risk to nervous, immune, renal, skeletal, and hematopoietic systems of both adult and children. Neurological, physiological, and behavioral disorders in children due to Pb exposure, are very common. According to the US Centers for disease control and prevention (CDC), 10 μg/dl or higher concentration of Pb in blood is considered as “elevated” or a “level of concern.” However, it has been shown that even blood Pb concentrations below 10 μg/dl are inversely associated with children's intelligence quotient (IQ) scores at three to five years of age. As a result of these findings, the CDC has recommended changes for the threshold of acceptable elevated blood Pb concentrations to 5 μg/dl.
6.3.2 Role of EDXRF in Diagnosis of Blood Lead Level
Lead (Pb) enters the body primarily by absorption through the gastrointestinal tract or by inhalation. It is estimated that about 11% of Pb in adults and 25–48% in children has been absorbed from the gastrointestinal track. After entering the body it infiltrates different bodily organs unequally. Pb concentrations in bone tissue rises from 8% to 90% after just 20 hours after entering in the body. Blood is the media responsible for transporting Pb throughout the body, and hence Pb can be monitored by measuring Pb concentrations in blood serum (S─Pb), blood plasma (P─Pb) or whole blood (W─Pb) samples. However, blood serum and blood plasma do not give a full indication of blood‐Pb level in a human body; therefore measurement Pb levels in whole blood is preferable to S─Pb or P─Pb measurements. According to Donald Smith et al. [14], Plasma Pb levels are approximately 0.29% on average of whole‐ blood Pb level.
Atomic absorption spectrometry (AAS), inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES), polarography, and inductively coupled plasma mass spectroscopy (ICP‐MS) have been used for determining blood Pb levels in S─Pb or P─Pb for years. But this poses problems, namely that all these techniques require large volumes of samples. Moreover they cannot measure whole blood samples, as these contain fat bodies. However, collection of biological samples in large volumes is very complicated. On the other hand sample preparation for those instruments requires special attention and is thus time‐consuming. In this case EDXRF is the only suitable tool for measuring Pb concentrations in whole blood samples as it requires only small amounts of sample material, and is nondestructive and versatile in comparison with other techniques.
6.3.3 Collection of Blood Sample and Preparation
Five milliliters of venous whole blood was drawn by disposable syringe. The blood sample was transferred immediately into a labeled container and stored in an ultra‐freezer at −20 °C to avoid any microbial growth. Blood samples should be collected in plastic containers prior to pretreatment and kept in a 20% nitric acid solution for 24 hours, properly rinsed with deionized water, and dried. The empty weight of all containers were taken before being stored in a plastic covering. The total weight of blood with containers was taken at room temperature. Subtracting the empty weight of the container gave the weight of the fresh sample. The samples were dried in an oven at 60–70 °C for four to six days. The dried samples were powdered in a carbide mortar with the help of a pestle and preserved in desiccators until subsequent analysis [15].
6.3.4 Preparation of Pellets from Powdered Sample
For the preparation of pellets, 100 mg of powdered blood sample was pressed into a pellet having diameter of 1 cm and thickness of 1 mm using a pellet maker (CARVER, 10 mm, model no:018735C) applying 3 tons of pressure (Figure 6.4). The pellet was then irradiated using an EDXRF machine [Figure 6.5].
6.3.5 Sample Irradiation
Irradiation of the sample pellet was done with a 30 m Ci Cd‐109 radioisotope annular source for about one thousand seconds to excite the characteristic X‐rays of the elements present in the sample. The X‐rays were detected with the Si (Li) detector of 170 eV resolution. The X‐ray spectrum of each sample was collected by a multichannel analyzer and transferred to a computer for storage, processing, and evaluation of the net X‐ray intensities. Commercial software “AXIL” installed on the system was employed for the qualitative and quantitative analysis of the respective elements in the sample. Detailed of the machine set up and its working principles are described elsewhere [16, 17].
Figure 6.4 Pellet of blood sample.
Figure 6.5 Energy dispersive X‐ray fluorescence (EDXRF) system.
6.3.6 Precision and Accuracy of the Result
EDXRF being a comparison method of elemental analysis requires the construction of a calibration curve to validate results. This curve is obtained by irradiating a commercially available standard reference material (SRM) (prepared in the same manner as the real sample) of a similar matrix. The basic concept operative here is that both the real sample and SRM should produce identical sensitivity, thus nullifying the matrix effect. In this study, commercially available standard reference material Spinach (NIST 1570a) was used to construct the calibration curve [15], taking into account that plants and blood have similar biological matrices. The constructed calibration curve has been validated by analyzing CRM (certified reference material) Orchard Leaf (NIST1571) and the obtained values were found to be in good agreement with the certified values. The relative error and coefficient of variation in percentage were in the acceptable range (<10%) as shown in Table 6.2.
6.4 Conclusion
Analysis of body tissue (urine, blood, plasma, nail, or hair) for the determination of its composition has become the most powerful and ubiquitous tool for disease detection and control in recent years. If there any case of suspected exposure to different toxic element (Pb, Cd, and As), measurement of those element by using EDXRF is an excellent technique. Moreover, the presence of even some essential elements in more than the required quantities in any body tissue, like iron in urine, or manganese in blood, that can cause organ malfunction or pathogen‐initiated disease can also be detected by EDXRF. In addition, it may be said that XRF analysis using EDXRF spectrometers is a unique technique for the identification and quantification of elements in any substance, including body tissue. It is a fast, accurate technique for the determination of elements in even very small quantities of samples. it is notable that, for the rapid, nondestructive clinical analysis of trace element recently XOS, the Alzheimer's Center of Albany Medical Center, Albany, NY, USA in colaboration with the Wadsworth Center (New York State Department of Health, Albany, NY, USA) started to measure trace elements of interest; potential diagnosis and treatment of neurodegenerative diseases using an NIH‐supported study (NIH 2R44RR021797‐02) toward development of an HD XRF‐based analyzer [18].
Table 6.2 Precision and accuracy of the method.
| Elements | Elemental concentration in Orchard leaf/NIST 1571 (mg/kg) | Mean | SD | Certified value Orchard leaf/NIST 1571 | RE (%) | CV (%) |
|---|---|---|---|---|---|---|