Method and portable facility for measurement of trace element concentration in prostate fluid samples using radionuclide-induced energy-dispersive X-ray fluorescent analysis

Method and portable facility for measurement of trace element concentration in prostate fluid samples using radionuclide-induced energy-dispersive X-ray fluorescent analysis 1 corresp first-author Corresponding author: E-mail address: vezai@obninsk.com Corresponding author: E-mail address: vezai@obninsk.com vezai@obninsk.com 2 1 Radionuclide Diagnostics Department, Medical Radiological Research Centre, Korolyev St. 4, Obninsk 249036, Russia. Radionuclide Diagnostics Department, Medical Radiological Research Centre, Korolyev St. 4, Obninsk 249036, Russia. Department of Medicine, University of Illinois, College of Medicine at Chicago, COMRB 1160-1168, Chicago, IL 60612, USA. Department of Medicine, University of Illinois, College of Medicine at Chicago, COMRB 1160-1168, Chicago, IL 60612, USA. A facility and method for 109 Cd radionuclide-induced energy dispersive X-ray fluorescent (EDXRF) were developed to determine the Fe, Zn, Br, Rb, and Sr concentrations in the specimens of human prostatic fluid. Specimens of expressed prostatic fluid were obtained from 51 men (mean age 51 years, range 18-82 years) with apparently normal prostates using standard rectal massage procedure. Mean values (M ± SΕΜ) for concentration of trace elements (mg·L -1 ) in human prostate fluid were: Fe 9.04±1.21, Zn 573±35, Br 3.58±0.59, Rb 1.10±0.08, and Sr ≤0.76. It was shown that the results of trace element analysis in the micro samples (20 μL) are sufficiently representative for assessment of the Fe, Zn, Br, and Rb concentration in the prostate fluid. The facility for 109 Cd radionuclide-induced EDXRF is comparatively compact and can be located in close proximity to the site of carrying out the massage procedure. The means of Zn and Rb concentration obtained for prostate fluid agree well with median of reported means. For the first time the Fe and Br concentrations, as well as the upper limit of the Sr concentration were determined in the human prostate fluid. Radionuclide-induced energy-dispersive X-ray fluorescent analysis Trace elements Human prostate Prostate fluid 109 Cd. 1 Introduction 1 The first finding of remarkable high level of Zn concentration in human prostatic fluid was reported in the beginning of 1960s [ 1 1 ] . Analyzing prostatic secretion expressed from prostate of 8 apparently healthy men aged 25-55 years it was found that Zn concentration varied in range from 300 to 730 mg/L. After this finding several investigators have suggested that the measurement of Zn level in expressed prostatic fluid may be useful as a marker of prostate secretory function [ 2 2 ] . It promoted a more detailed study of prostatic fluid Zn concentration in healthy subjects and in those with different prostate diseases: chronic prostatitis, benign prostatic hyperplasia (BPH) and prostate cancer (PCa). A detailed review of these studies, reflecting the contradictions within accumulated data, was given in our earlier publication [ 3 3 ] . The studies of Zn in prostatic fluid expressed from normal and neoplastic prostate glands were done in the second half of 1970s in the Medical Radiological Research Center in Obninsk, Russia (MRRC) using nondestructive nuclear analytical methods. Nondestructive methods of analysis avoid the possibility of changing the Zn content in the studied samples during sample preparation, which allowed for the first time to obtain reliable results. In particular, it was shown that the average concentration of Zn in prostatic fluid in cancerous gland is 15-17 times lower than in healthy or hyperplastic prostates [ 3 3 ] . Obtained results formed the basis for a new method for differential diagnosis of BPH and PCa, the essence of which was to determine the Zn concentration in the sample of expressed prostatic fluid. For the first time it was proposed to use energy dispersive X-ray fluorescence (EDXRF) to determine Zn concentration in the sample of expressed prostatic fluid. The method has been successfully used in clinical trials of MRRC, and it was patented in Russia [ 4 4 ] . All data on the new method of diagnosing PCa were classified by Ministry of Health of the USSR, and publications were made possible only in the 90's, after the radical political changes in the country. Publications in international scientific journals [ 3 3 ] and presentations at international medical conferences [ 5 5 , 6 6 ] have stimulated the interest in new approaches for early diagnosis of PCa based on the phenomenon of a sharp reduction in the ability of the prostate fluid to accumulate Zn after malignant transformation of gland. Currently, work in this direction is carried out in several research centers and hospitals in the United States [ 7 7 , 8 8 ] , and other countries [ 9 9 ] . To a large extent, the resumption of the search for new methods for early diagnosis of PCa was due to gained experience in a critical assessment of the capacity of the PSA serum test [ 10 10 ] . In order to determine Zn concentration in the sample of expressed prostatic fluid, one can use commercially available systems of different analytical methods like EDXRF, AAS, ICP-AES, ICP-MS, and others. Each of these methods has advantages and disadvantages, the discussion of which is beyond the scope of this work. To determine Zn concentration in the sample of expressed prostatic fluid, we have chosen radionuclide-induced EDXRF. A simple inexpensive device that uses a miniature source of exciting radiation from 109 Cd radionuclide was developed by us. Our decision was based on two reasons. First, large radiology centers usually have a Spectrometric Laboratory for the measurement of radiations, including photons of 1-100 keV, and such equipment eliminates one’s need additional expensive purchases to use EDXRF. Secondly, the volume of expressed prostatic fluid sample as usual does not exceed a few tens of microliters. Thus, the ultimate goal of research conducted in the MRRC was to develop a method for measurement of Zn concentration in the sample with volume equal one drop (nearly 20 μL) of prostatic fluid and to create a miniature X-ray fluorescence device available for PCa screening. We believe that the creation of such a device is possible on the basis of EDXRF analysis using a miniature radionuclide sources. Therefore, EDXRF analysis experience, using 109 Cd source to determine Zn concentration in the sample of expressed prostatic fluid might be useful for further development of PCa screening. Our previous studies found that not only Zn but many others trace elements may be useful as tumor markers [ 11 11 - 22 22 11-22 ] . Thus, this work had three aims. The first one was to present the design of the method and apparatus for micro analysis of Zn and some other trace elements in the samples of expressed prostatic fluid using EDXRF with radionuclide source 109 Cd. The second aim was to evaluate the quality of obtained results, and the third - to assess the concentration of Br, Fe, Rb, Sr, and Zn in expressed prostatic fluid of normal prostate gland. The study was approved by the Ethical Committee of the Medical Radiological Research Center, Obninsk. 2 Experimental Section 1 Specimens of expressed prostatic fluid were obtained from 51 men (mean age 51 years, range 18-82 years) with apparently normal prostates by qualified urologists in the Urological Department of the Medical Radiological Research Centre using standard rectal massage procedure. Subjects were asked to abstain from sexual intercourse for 3 days preceding the procedure. Specimens of expressed prostatic fluid were obtained in sterile containers which were appropriately labeled. Twenty μL (microliters) of fluid were taken by micropipette from every specimen for trace element analysis, while the rest of the fluid was used for cytological and bacteriological investigations. The chosen 20 μL of the expressed prostatic fluid was dropped on 11.3 mm diameter disk made of thin, ash-free filter papers fixed on the Scotch tape pieces and dried in an exsiccator at room temperature. Then the dried sample was covered with 4 μm Dacron film and centrally pulled onto a Plexiglas cylindrical frame ( Fig. 1 Fig. 1 ). To determine concentration of the elements by comparison with a known standard, aliquots of solutions of commercial, chemically pure compounds were used for a device calibration [ 23 23 ] . The standard samples for calibration were prepared in the same way as the samples of prostate fluid. Because there were no available liquid Certified Reference Material (CRM) ten sub-samples of the powdery CRM IAEA H-4 (animal muscle) were analyzed to estimate the precision and accuracy of results. Every CRM sub-sample weighing about 3 mg was applied to the piece of Scotch tape serving as an adhesive fixing backing. An acrylic stencil made in the form of a thin-walled cylinder with 11.3 mm inner diameter was used to apply the sub-sample to the Scotch tape. The polished-end acrylic pestle which is a constituent of the stencil set was used for uniform distribution of the sub-sample within the Scorch surface restricted by stencil inner diameter. When the sub-sample was slightly pressed to the Scotch adhesive sample, the stencil was removed. Then the sub-sample was covered with 4 μm Dacron film. Before the sample was applied, pieces of Scotch tape and Dacron film were weighed using analytical balance. Those were again weighed together with the sample inside to determine the sub-sample mass precisely. The facility for radionuclide-induced energy dispersive X-ray fluorescence included an annular 109 Cd source with an activity of 2.56 GBq, Si(Li) detector with electric cooler and portable multi-channel analyzer combined with a PC. Its resolution was 270 eV at the 6.4 keV line. The facility functioned as follows. Photons with a 22.1 keV 109 Cd energy are sent to the surface of a specimen analyzed inducing the fluorescence K α X-rays of trace elements. The fluorescence irradiation got to the detector through a 10 mm diameter collimator to be recorded. The duration of the Zn concentration measurement was 10 min. The duration of the Zn concentration measurement together with Br, Fe, Rb, and Sr was 60 min. The intensity of K α -line of Br, Fe, Rb, Sr, and Zn for samples and standards was estimated on calculation basis of the total area of the corresponding photopeak in the spectra. The trace element concentration was calculated by the relative way of comparing between intensities of K α -lines for samples and standards. Following the assumption that the surface density of dried samples and standards meets the criterion of “thin sample” [ 24 24 , 25 25 ] , the trace element concentration in the sample ( C s ) can be calculated from the following simple relation: <math display="block" id="M1"><mrow><msub><mi>C</mi><mtext>s</mtext></msub><mo>=</mo><mtext> </mtext><mo stretchy="false">(</mo><msub><mi>Q</mi><mrow><mtext>st</mtext></mrow></msub><mo>×</mo><msub><mi>N</mi><mtext>s</mtext></msub><mo stretchy="false">)</mo><mtext> </mtext><mo>/</mo><mtext> </mtext><mo stretchy="false">(</mo><msub><mi>m</mi><mtext>s</mtext></msub><mo>×</mo><msub><mi>N</mi><mrow><mtext>st</mtext></mrow></msub><mo stretchy="false">)</mo><mo>,</mo></mrow></math> where N s and N st are trace element K α -line intensity (counts per minute) in the sample and standard spectra, respectively; m s is the sample mass (kg) or volume (L); Q st is trace element content in the standard (mg). The relative counting statistical uncertainty (“statistical error”) and the detection limit (DL) depends on mass of the sample and the duration of measurement. The “statistical error” of zinc K α -line measurement for 10 min of most prostate fluid samples did not exceed 3.0%. The DL (mg/L) for the Fe, Br, Rb, Sr, and Zn, determination in 20 μL sample of dry prostate fluid sample with 60 min measurement was about 2.0, 0.5, 0.3, 0.1, and 1.0, respectively. The detection limit of element was calculated as: <math display="block" id="M2"><mrow><mi>D</mi><mi>L</mi><mo>=</mo><mtext> </mtext><mrow><mo>(</mo><mrow><mn>3</mn><mo>√</mo><msub><mi>N</mi><mtext>b</mtext></msub></mrow><mo>)</mo></mrow><mtext> </mtext><mo>/</mo><mi>R</mi><mi>F</mi><mi>，</mi></mrow></math> where N b is the background intensity in K α -line area of corresponding element, and RF is a response function for this element: <math display="block" id="M3"><mrow><mi>R</mi><mi>F</mi><mo>=</mo><mtext> </mtext><mrow><mo>(</mo><mrow><msub><mi>N</mi><mrow><mtext>st</mtext></mrow></msub><mo>−</mo><msub><mi>N</mi><mtext>b</mtext></msub></mrow><mo>)</mo></mrow><mtext> </mtext><mo>/</mo><msub><mi>C</mi><mrow><mtext>st</mtext></mrow></msub><mi>，</mi></mrow></math> where N st is the intensity of corresponding K α -line for the standard and C st is trace element concentration in the standard (mg/L). Using the Microsoft Office Excel program to provide a summary of statistical results, the arithmetic mean, standard deviation, standard error of mean, minimum and maximum values, median, percentiles with 0.025 and 0.975 levels were calculated for all the chemical element concentrations obtained. 3 Results and Discussion 1 Figures 1 Figures 1 and 2 2 depict the dried samples of prostate fluid prepared for the analysis and the facility for Fe, Zn, Br, Rb, and Sr concentration measurement in prostate fluid samples by the 109 Cd radionuclide-induced EDXRF, respectively. Table 1 Table 1 present our calculation which to need for an estimation of the maximum surface density of the “thin sample” for 109 Cd radionuclide-induced EDXRF analysis of Fe content in samples of dry and wet prostate fluid using published data on fluid chemical composition [ 3 3 , 4 4 , 7 7 , 26 26 , 27 27 , 28 28 , 29 29 , 30 30 , 31 31 , 32 32 ] and photon cross sections [ 33 33 ] . Table 2 Table 2 shows 109 Cd radionuclide-induced EDXRF data for Fe, Zn, Br, Rb, and Sr mass fractions in sub-samples of certified reference materials IAEA H-4 (animal muscle) and the certified values of this material. Table 3 Table 3 represents some basic statistical parameters (arithmetic mean, standard deviation, relative standard deviation, standard error of mean, minimal and maximal values, median, percentiles with 0.025 and 0.975 levels) of Fe, Zn, Br, Rb, and Sr concentration (mg·L -1 ) in human prostate fluid. The comparison of our results with published data for Fe, Zn, Br, Rb, and Sr concentration in the prostate fluid expressed out of a normal human gland [ 4 4 , 34 34 , 35 35 ] is shown in Table 4 Table 4 . The estimation of repeatability of the 109 Cd radionuclide-induced EDXRF results for Fe, Zn, Br, Rb, and Sr concentrations determined in 3 sub-samples taken from few specimens of prostate fluid is shown in Table 5 Table 5 . a Mean concentrations for prostate tissue are calculated based on reference data [ 3 3 , 4 4 , 7 7 , 25 25 - 31 31 25-31 ]. b Values of <math id="M8"><mrow><msubsup><mi>μ</mi><mi>i</mi><mn>1</mn></msubsup></mrow></math> and <math id="M9"><mrow><msubsup><mi>μ</mi><mi>i</mi><mn>2</mn></msubsup></mrow></math> are calculated from data of Marenkov et al. [ 32 32 ]. c <math id="M10"><mrow><mover accent="true"><mi>μ</mi><mo>¯</mo></mover><mo>=</mo><mo stretchy="false">(</mo><msubsup><mi>μ</mi><mi>i</mi><mn>1</mn></msubsup><mo>/</mo><mi mathvariant="normal">Sin</mi><mi>ϑ</mi><mo stretchy="false">)</mo><mo>+</mo><mo stretchy="false">(</mo><msubsup><mi>μ</mi><mi>i</mi><mn>2</mn></msubsup><mo>/</mo><mi mathvariant="normal">Sin</mi><mi>ψ</mi><mo stretchy="false">)</mo></mrow></math> , where ϑ is an incidence angle of excitation beam (30 0 ), ψ is a reflection angle of detection beam (90°). 1 1 Element 2 1 Concentration and mass fraction (c i ) a 1 1 <math id="M4"><mrow><msubsup><mi>μ</mi><mi>i</mi><mrow><mn>1</mn><mtext>b</mtext></mrow></msubsup></mrow></math> 1 1 <math id="M5"><mrow><msubsup><mi>μ</mi><mi>i</mi><mrow><mn>2</mn><mtext>b</mtext></mrow></msubsup></mrow></math> 1 1 <math id="M6"><mrow><msubsup><mover accent="true"><mi>μ</mi><mo>¯</mo></mover><mi>i</mi><mtext>c</mtext></msubsup></mrow></math> (cm 2 g -1 ) 2 1 <math id="M7"><mrow><msub><mi>c</mi><mi>i</mi></msub><mtext> </mtext><msub><mover accent="true"><mi>μ</mi><mo>¯</mo></mover><mi>i</mi></msub></mrow></math> (cm 2 g -1 ) 1 1   1 1 Wet prostate fluid (g·ml -1 ) 1 1 Dry prostate fluid (g·g -1 ) 1 1 22.1 keV 109 Cd(сm 2 ·g -1 ) 1 1 6.40keV K α Fe(сm 2 ·g -1 ) 1 1   1 1 Wet tissue of prostate 1 1 Dry tissue of prostate 1 1 H 1 1 0.1000000 1 1 0.0600000 1 1 0.365 1 1 0.399 1 1 1.13 1 1 0.112900 1 1 0.067740 1 1 C 1 1 0.0370000 1 1 0.5000000 1 1 0.375 1 1 8.97 1 1 9.72 1 1 0.359640 1 1 4.860000 1 1 N 1 1 0.0110000 1 1 0.1400000 1 1 0.512 1 1 14.7 1 1 15.72 1 1 0.172964 1 1 2.201360 1 1 O 1 1 0.8420000 1 1 0.1800000 1 1 0.695 1 1 22.6 1 1 23.99 1 1 20.199580 1 1 4.318200 1 1 Na 1 1 0.0030000 1 1 0.0400000 1 1 1.583 1 1 57.8 1 1 60.97 1 1 0.182898 1 1 2.438640 1 1 Mg 1 1 0.0004860 1 1 0.0069000 1 1 2.100 1 1 76.8 1 1 81.00 1 1 0.039366 1 1 0.558900 1 1 P 1 1 0.0000340 1 1 0.0004800 1 1 3.999 1 1 144 1 1 152.00 1 1 0.005168 1 1 0.072959 1 1 S 1 1 0.0014000 1 1 0.0200000 1 1 5.002 1 1 177 1 1 187.00 1 1 0.261806 1 1 3.740080 1 1 Cl 1 1 0.0010000 1 1 0.0100000 1 1 6.421 1 1 225 1 1 237.84 1 1 0.237842 1 1 2.378420 1 1 K 1 1 0.0018000 1 1 0.0250000 1 1 8.100 1 1 273 1 1 289.20 1 1 0.520560 1 1 7.230000 1 1 Ca 1 1 0.0008000 1 1 0.0100000 1 1 9.706 1 1 318 1 1 337.41 1 1 0.269930 1 1 3.374120 1 1 Mn 1 1 0.0000010 1 1 0.0000143 1 1 16.97 1 1 61.2 1 1 95.14 1 1 0.000095 1 1 0.001361 1 1 Fe 1 1 0.0000090 1 1 0.0001290 1 1 19.41 1 1 70.9 1 1 109.72 1 1 0.000987 1 1 0.014154 1 1 Cu 1 1 0.0000004 1 1 0.0000057 1 1 25.68 1 1 95.2 1 1 146.56 1 1 0.000059 1 1 0.000835 1 1 Zn 1 1 0.0004500 1 1 0.0064290 1 1 28.42 1 1 106 1 1 162.84 1 1 0.073278 1 1 1.046898 1 1 Br 1 1 0.0000030 1 1 0.0000429 1 1 40.62 1 1 163 1 1 244.24 1 1 0.000733 1 1 0.010478 1 1 Rb 1 1 0.0000020 1 1 0.0000286 1 1 46.15 1 1 191 1 1 283.30 1 1 0.000567 1 1 0.008102 1 1 Sr 1 1 0.0000010 1 1 0.0000143 1 1 49.27 1 1 208 1 1 306.54 1 1 0.000307 1 1 0.004384 1 1 Cd 1 1 0.0000001 1 1 0.0000014 1 1 14.45 1 1 408 1 1 436.90 1 1 0.000044 1 1 0.000612 1 1 Σ c i 1 1 0.999 1 1 0.999 1 1   1 1   1 1 Σ c i ·μ i 1 1 22.44 1 1 32.33 Mean – arithmetical mean, SD – standard deviation, C - certified values, N – non-certified values. 1 1 Element 3 1 Certified values 1 1 This work results 1 1   1 1 Mean 1 1 95% confidence interval 1 1 Type 1 1 Mean±SD 1 1 Fe 1 1 49 1 1 47 - 51 1 1 С 1 1 48±9 1 1 Zn 1 1 86 1 1 83 - 90 1 1 C 1 1 90±5 1 1 Br 1 1 4.1 1 1 3.5 – 4.7 1 1 C 1 1 5.0±1.2 1 1 Rb 1 1 18 1 1 17 - 20 1 1 C 1 1 22±4 1 1 Sr 1 1 0.1 1 1 - 1 1 N 1 1 <1 M - arithmetic mean, SD – standard deviation, SEM – standard error of mean, Min – inimum value, Max – maximum value, Per. 0.025 – percentile with 0.025 level, Per. 0.975 – percentile with 0.975 level, DL – detection limit. 1 1 Element 1 1 Mean 1 1 SD 1 1 RSD(%) 1 1 SEM 1 1 Min 1 1 Max 1 1 Median 1 1 Per. 0.025 1 1 Per. 0.975 1 1 Fe 1 1 9.04 1 1 7.28 1 1 80.5 1 1 1.21 1 1 1.27 1 1 39.8 1 1 7.84 1 1 1.29 1 1 21.3 1 1 Zn 1 1 573 1 1 202 1 1 35.3 1 1 28 1 1 253 1 1 948 1 1 552 1 1 260 1 1 941 1 1 Br 1 1 3.58 1 1 3.31 1 1 92.5 1 1 0.59 1 1 0.16 1 1 10.0 1 1 1.63 1 1 0.19 1 1 9.16 1 1 Rb 1 1 1.10 1 1 0.51 1 1 46.4 1 1 0.08 1 1 0.38 1 1 2.45 1 1 1.03 1 1 0.41 1 1 2.36 1 1 Sr 1 1 ≤0.76 1 1 - 1 1 - 1 1 - 1 1 <0.1(DL) 1 1 3.44 1 1 - 1 1 - 1 1 - M - arithmetic mean, SD – standard deviation, ( n ) a – number of all references, ( n ) b - number of samples. 1 1 Element 3 1 Published data [Reference] 1 2 This work results M±SD 1 1   1 1 Median of means( n ) a 1 1 Minimumof means M or M±SD, ( n ) b 1 1 Maximumof means M±SD, ( n ) b 1 1 Fe 1 1 - 1 1 - 1 1 - 1 1 9.04±7.28 1 1 Zn 1 1 453 (19) 1 1 47.1(-) [ 32 32 ] 1 1 9870±10130 (11) [ 33 33 ] 1 1 573±202 1 1 Br 1 1 - 1 1 - 1 1 - 1 1 3.58±3.31 1 1 Rb 1 1 2.26 (1) 1 1 1.11±0.57 (15) [ 4 4 ] 1 1 2.35±1.85 (11) [ 4 4 ] 1 1 1.10±0.51 1 1 Sr 1 1 - 1 1 - 1 1 - 1 1 ≤0.76 Mean – arithmetical mean, SD – standard deviation, RSD – relative standard deviation, DL – detection limit. 1 1 Element 1 1 Specimen No 3 1 Sub-sample 1 1 Mean 1 1 SD 1 1 RSD (%) 1 1 Mean RSD (%) 1 1   1 1   1 1 No 1 1 1 No 2 1 1 No 3 1 1   1 1   1 1   1 1   1 1 Fe 1 1 55 1 1 12.3 1 1 10.2 1 1 14.2 1 1 12.2 1 1 2.00 1 1 16.4 1 1 11.0 1 1   1 1 59 1 1 17.3 1 1 16.0 1 1 18.7 1 1 17.3 1 1 1.35 1 1 7.8 1 1   1 1   1 1 61 1 1 7.3 1 1 7.1 1 1 7.6 1 1 7.33 1 1 0.25 1 1 3.4 1 1   1 1   1 1 62 1 1 7.3 1 1 8.7 1 1 8.8 1 1 8.27 1 1 0.84 1 1 10.1 1 1   1 1   1 1 65 1 1 14.0 1 1 19.8 1 1 16.5 1 1 16.8 1 1 2.91 1 1 17.4 1 1   1 1 Zn 1 1 55 1 1 740 1 1 552 1 1 628 1 1 640 1 1 94.6 1 1 14.8 1 1 8.3 1 1   1 1 59 1 1 549 1 1 614 1 1 493 1 1 552 1 1 60.6 1 1 11.0 1 1   1 1   1 1 61 1 1 566 1 1 555 1 1 578 1 1 566 1 1 11.5 1 1 2.0 1 1   1 1   1 1 62 1 1 593 1 1 662 1 1 625 1 1 627 1 1 34.5 1 1 5.5 1 1   1 1   1 1 65 1 1 458 1 1 533 1 1 470 1 1 487 1 1 40.3 1 1 8.3 1 1   1 1 Br 1 1 55 1 1 1.46 1 1 1.57 1 1 1.30 1 1 1.44 1 1 0.14 1 1 9.4 1 1 29.9 1 1   1 1 59 1 1 5.46 1 1 7.66 1 1 3.26 1 1 5.46 1 1 2.20 1 1 40.3 1 1   1 1   1 1 61 1 1 3.57 1 1 5.83 1 1 1.32 1 1 3.57 1 1 2.26 1 1 63.1 1 1   1 1   1 1 62 1 1 8.92 1 1 7.74 1 1 10.0 1 1 8.89 1 1 1.13 1 1 12.7 1 1   1 1   1 1 65 1 1 8.53 1 1 8.53 1 1 5.45 1 1 7.50 1 1 1.78 1 1 23.7 1 1   1 1 Rb 1 1 55 1 1 1.35 1 1 1.03 1 1 1.67 1 1 1.35 1 1 0.32 1 1 23.7 1 1 22.3 1 1   1 1 59 1 1 1.31 1 1 1.56 1 1 1.06 1 1 1.31 1 1 0.25 1 1 19.1 1 1   1 1   1 1 61 1 1 0.44 1 1 0.38 1 1 0.85 1 1 0.56 1 1 0.26 1 1 46.0 1 1   1 1   1 1 62 1 1 0.41 1 1 0.41 1 1 0.49 1 1 0.44 1 1 0.05 1 1 10.6 1 1   1 1   1 1 65 1 1 1.03 1 1 1.15 1 1 0.90 1 1 1.03 1 1 0.13 1 1 12.2 1 1   1 1 Sr 1 1 55 1 1 <DL 1 1 <DL 1 1 <DL 1 1 - 1 1 - 1 1 - 1 1 - 1 1   1 1 59 1 1 1.33 1 1 1.29 1 1 1.37 1 1 1.33 1 1 0.04 1 1 3.0 1 1   1 1   1 1 61 1 1 <DL 1 1 <DL 1 1 <DL 1 1 - 1 1 - 1 1 - 1 1   1 1   1 1 62 1 1 <DL 1 1 <DL 1 1 <DL 1 1 - 1 1 - 1 1 - 1 1   1 1   1 1 65 1 1 1.97 1 1 3.44 1 1 1.50 1 1 2.30 1 1 1.01 1 1 43.9 1 1   Distribution of trace elements on filter paper disk in the samples prepared for 109 Cd radionuclide-induced EDXRF can be inhomogeneous. To reverse the effect of inhomogeneous distribution of the element on the outcome of the analysis we have used annular 109 Cd source, providing an even distribution of exciting radiation at the surface of the sample ( Fig.2 Fig.2 ). In addition to photons with 22.16 keV (Ag K α1 ), 21.99 keV (Ag K α2 ), 24.9 keV (Ag K β1 ), and 25.5 keV (Ag K β2 ), a 109 Cd source emits gamma-quanta with energy 88 keV (output 4.2%). To protect the crystal detector from a direct hit of 88 keV gamma-quanta we designed a tantalum shield ( Fig.2 Fig.2 ). The choice of a suitable geometry in «source - sample - detector crystal» was based on the results of a special study [ 36 36 ] . By definition, the "thin sample" self-absorption does not exceed 10% [ 24 24 , 25 25 ] . In the process of 109 Cd radionuclide-induced EDXRF, samples and standards meet the criterion of “thin sample” provided their surface density ( ρ ·d ) did not exceed the following value: <math display="block" id="M11"><mrow><mi>ρ</mi><mo>·</mo><mi>d</mi><mo>≤</mo><mfrac><mrow><mn>0.1</mn></mrow><mrow><mstyle displaystyle="true"><munder><mo>∑</mo><mrow/></munder><mrow><msub><mi>c</mi><mi>i</mi></msub><mover accent="true"><mrow><mo>⋅</mo><msub><mi>μ</mi><mi>i</mi></msub></mrow><mo stretchy="true">¯</mo></mover></mrow></mstyle></mrow></mfrac><mo>,</mo></mrow></math> where ρ is mass density of the analysed sample, d is a sample thickness, c i is a relative individual mass fraction of the element in the sample, <math id="M12"><mrow><msub><mover accent="true"><mi>μ</mi><mo>¯</mo></mover><mi>i</mi></msub></mrow></math> is a mean value of the total mass attenuation coefficient of exciting and characteristic radiation with regard to geometry in the system of “source-sample-detector” [ 24 24 , 25 25 , 36 36 ] . The value of Σ c i · μ i is 22.4 cm 2 ·g -1 and 33.2 cm 2 ·g -1 for Fe (element with lowest characteristic X-ray radiation 6.4 keV measured in the study) in the wet and dry prostate fluid sample, respectively ( Table 1 Table 1 ). It follows that samples of dry prostate fluid meet the criterion of “thin sample” only in case if their surface density does not exceed 0.0030 g·cm -2 . The sample mass of dry prostate fluid which fills the backing area of 1 cm 2 (11.3 mm diameter filter paper disk) should not exceed 3.0 mg. The content of H 2 O in the prostate fluid equals 93% [ 27 27 ] . Therefore, dry mass of 20 μL prostate fluid sample (1.4 mg) is under the limit. We can accept that chemical matrix of dried animal muscle is similar to matrix of dried prostate fluid (both are mainly proteins). Thus, the results of calculation showed that the prepared prostate fluid and CRM IAEA H-4 samples conformed to the criterion of “thin sample”. In its turn, the conformity of samples and standards with the criterion of “thin sample” confirmed the competence of using the chosen way for calculation of Fe contents in the analysed samples. Energies of K α X-rays of Zn, Br, Rb, and Sr are higher than K α Fe. It means that the prepared samples complied with the criterion of “thin sample” for the measurement of Zn, Br, Rb, and Sr contents too. Good agreement of the Fe, Zn, Br, Rb, and Sr contents analyzed by 109 Cd radionuclide-induced EDXRF with the certified data of CRM IAEA H-4 ( Table 2 Table 2 ) indicate an acceptable accuracy of the results obtained in the study of trace elements of the prostate fluid presented in Tables 3 Tables 3 - 5 5 . The 109 Cd radionuclide-induced EDXRF allowed the assessment of the mean concentrations or an upper limit of concentration of 5 trace elements (Fe, Zn, Br, Rb, and Sr) in the micro samples (20 μL) of prostate fluid. The contents of Fe, Zn, Br, and Rb were measured in all or a major portion of prostate fluid samples. Mean values (M±SΕΜ) for concentrations (mg·L -1 ) of 4 trace elements in the prostate fluid between ages 18-82 years were: Fe – 9.0±1.2, Zn – 573±28, Br – 3.58±0.59, and Rb – 1.10±0.08 ( Table 3 Table 3 ). The Sr concentration was determined in a few samples. The possible upper limit of the mean (≤M) for this trace element was calculated as the average concentration, using the value of the detection limit (DL=0.1 mg·L -1 ) instead of the individual value when the latter was found to be below the DL: <math display="block" id="M13"><mrow><mo>≤</mo><mi>M</mi><mo>=</mo><mrow><mo>(</mo><mrow><mstyle displaystyle="true"><munderover><mo>∑</mo><mi>i</mi><mrow><msub><mi>n</mi><mi>i</mi></msub></mrow></munderover><mrow><msub><mi>C</mi><mi>i</mi></msub><mo>+</mo><mi>D</mi><mi>L</mi><mo>⋅</mo><msub><mi>n</mi><mi>j</mi></msub></mrow></mstyle></mrow><mo>)</mo></mrow><mo>/</mo><mi>n</mi><mo>,</mo></mrow></math> where Ci is the individual value of the trace-element mass fraction in sample -i , n i is number of samples with mass fraction higher than the DL, n j is number of samples with mass fraction lower than the DL, and n = n i + n j is number of samples that were investigated. The upper limit of mass fraction of this trace element was: Sr ≤1.05 mg·L -1 . The mean values concentrations and all selected statistical parameters were calculated for Fe, Zn, Br, and Rb in the prostate fluid of apparently healthy males aged 18-82 years ( Table 3 Table 3 ). The mean of Zn concentration obtained for prostate fluid, as shown in Table 4 Table 4 , agrees well with median of means cited by other researches [ 1 1 - 4 4 1-4 , 9 9 , 29 29 - 32 32 29-32 , 34 34 , 35 35 ] . The mean of Rb concentration obtained for prostate fluid agrees well with our data reported 35 years ago [ 4 4 ] . No published data referring to Fe, Br, and Sr concentrations in prostate fluid were found. Uncertainties expressed as mean relative standard deviation of the 109 Cd radionuclide-induced EDXRF results from Fe, Zn, Br, and Rb determination in 3 sub-samples of 5 prostate fluid specimens were 11%, 8%, 30% and 22%, respectively ( Table 5 Table 5 ). These values of result uncertainties are 2-7 times lower than RSD connected to individual variations of the Fe, Zn, Br, and Rb concentrations in prostate fluid– 81%, 35%, 93%, and 46%, respectively (see Table 3 Table 3 ). It means that developed method of Fe, Zn, Br, and Rb measurement in micro specimens of prostate fluids is acceptable for using in clinical studies [ 37 37 , 38 38 ] . The 109 Cd radionuclide-induced EDXRF analysis developed to determine the Fe, Zn, Br, Rb, and Sr concentrations in prostate fluid samples is a nondestructive method. It has a great advantage over destructive analytical methods. Almost all analytical methods used for chemical element measurements in prostate fluid were based on investigation of processed fluid with a goal to destroy and remove organic matrix. In such studies prostate fluid samples were acid digested or dried and then ashed before analysis. There is evidence that certain quantities of chemical elements are lost as a result of such treatment [ 39 39 - 41 41 39-41 ] . Thus, when using destructive analytical methods it is necessary to control for the losses of trace elements, for complete acid digestion of the sample, and for the contaminations by trace elements during sample decomposition, which needs adding some chemicals. It is possible to avoid these not easy procedures using non-destructive methods, including the 109 Cd radionuclide-induced EDXRF. The 109 Cd radionuclide-induced EDXRF developed to determine trace element concentrations in prostate fluid is micro method because sample volume 20 μL (one drop) is quite enough for analysis. It is another advantage of the method. Amount of human prostatic fluid collected by massage of the normal prostate is usually in range 100-500 μL [ 25 25 ] but in a pathological state of gland, particularly after malignant transformation, this amount may be significantly lower. Therefore, the micro method of 109 Cd radionuclide-induced EDXRF developed to determine trace element concentrations in prostate fluid is available for using in clinical studies. 4 Conclusion 1 The facility and method for 109 Cd radionuclide-induced EDXRF were developed to determine the Fe, Zn, Br, Rb, and Sr concentrations in the micro samples (20 μL) of expressed prostate fluid. The results of trace element analysis in the micro samples are sufficiently representative for assessment of the Fe, Zn, Br, and Rb concentration in the prostate fluid. The 109 Cd radionuclide-induced EDXRF analysis of Fe, Zn, Br, Rb, and Sr concentration in the prostate fluid requires no preliminary sample preparation; it is non-destructive and takes not more than 10 min for Zn and 60 min for all trace element measurement. The facility for 109 Cd radionuclide-induced EDXRF is comparatively compact and can be located in close proximity to the site of carrying out the massage procedure. The means of Zn and Rb concentration obtained for prostate fluid agree well with median of reported means. For the first time the Fe, Br, and Sr concentrations were determined in the human prostate fluid. References A.R. Mackenzie , T. Hall , Jr W.F. Whitmore . Zinc content of expressed human prostate fluid . Nature (London) 193 ( 4810 ), 72 - 73 ( 1962 ). Zinc content of expressed human prostate fluid J.L. Marmar , S. Katz , D.E. Praiss , T.J. DeBenedictis . Values for zinc in whole semen, fraction of split ejaculate and expressed prostatic fluid . Urology 16 ( 5 ), 478 - 480 ( 1980 ) doi: 10.1016/0090-4295(80)90599-3 http://doi.org/10.1016/0090-4295(80)90599-3 Values for zinc in whole semen, fraction of split ejaculate and expressed prostatic fluid V. Zaichick , T. Sviridova , S. Zaichick . Zinc concentration in human prostatic fluid: normal, chronic prostatitis, adenoma, and cancer . Int. Urol. Nephrol . 28 ( 5 ), 687 - 694 ( 1996 ) http://www.ncbi.nlm.nih.gov/pubmed/9061429 http://www.ncbi.nlm.nih.gov/pubmed/9061429 Zinc concentration in human prostatic fluid: normal, chronic prostatitis, adenoma, and cancer V. Zaichick , A. Tsyb , V.N. Dunchik , T.V. Sviridova . Method for diagnostics of prostate diseases . Certificate of invention No 997281 ( 30.03.1981 ). Method for diagnostics of prostate diseases V. Zaichick , A. Tsyb . In vitro and in vivo radiation techniques of the element analysis for cancer diagnostics . In: International Congress of Radiation Oncology - ICRO’93 (21-25 June 1993) . Kyoto, Japan , p. 410 ( 1993 ). In vitro and in vivo radiation techniques of the element analysis for cancer diagnostics V. Zaichick , A. Tsyb . Nuclear methods of chemical element analysis in body tissues and fluids for cancer diagnostics . Eur. J. Nucl. Med . 23 ( 9 ), 1220 ( 1996 ). Nuclear methods of chemical element analysis in body tissues and fluids for cancer diagnostics L.C. Costello , R.B. Franklin . Prostatic fluid electrolyte composition for the screening of prostate cancer: a potential solution to a major problem . Prostate Cancer Prostate Dis . 12 ( 1 ), 17 - 24 ( 2009 ). doi: 10.1038/pcan.2008.19 http://doi.org/10.1038/pcan.2008.19 . Prostatic fluid electrolyte composition for the screening of prostate cancer: a potential solution to a major problem Z. Medarova , S.K. Ghosh , M. Vangel et al . Risk stratification of prostate cancer patients based on EPS-urine zinc content . Am. J. Cancer. Res . 4 ( 4 ), 385 - 393 , ( 2014 ). http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4106656/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4106656/ Risk stratification of prostate cancer patients based on EPS-urine zinc content Y. Gómez , F. Arocha , F. Espinoza et al . Zinc levels in prostatic fluid of patients with prostate pathologies . Invest. Clin . 48 ( 3 ), 287 - 294 ( 2007 ) Zinc levels in prostatic fluid of patients with prostate pathologies K. Lin , R. Lipsitz , T. Miller et al . Benefits and harms of prostate-specific antigen screening for prostate cancer: an evidence update for the U.S. Preventive Services Task Force . Ann. Intern. Med . 149 ( 3 ), 192 - 199 ( 2008 ). doi: 10.7326/0003-4819-149-3-200808050-00009 http://doi.org/10.7326/0003-4819-149-3-200808050-00009 Benefits and harms of prostate-specific antigen screening for prostate cancer: an evidence update for the U.S. Preventive Services Task Force V. Zaichick V . Iodine and some other trace elements of the thyroid gland: Standard and Disease . In: Nuclear Analytical Methods in the Life Sciences (13-17 Sept 1993) . Prague , 32 - 33 ( 1993 ). Iodine and some other trace elements of the thyroid gland: Standard and Disease V. Zaichick . Instrumental activation and X-ray fluorescent analysis of human bones in health and disease . J. Radioanal. Nucl. Chem . 179 ( 2 ), 295 - 303 ( 1994 ). Instrumental activation and X-ray fluorescent analysis of human bones in health and disease V. Zaichick , A. Tsyb , B.M. Vtyurin . Trace elements and thyroid cancer . Analyst 120 , 817 - 821 ( 1995 ) http://www.ncbi.nlm.nih.gov/pubmed/7741233 http://www.ncbi.nlm.nih.gov/pubmed/7741233 Trace elements and thyroid cancer S. Zaichick , V. Zaichick . Trace elements of normal, benign hypertrophic and cancerous tissues of the human prostate gland investigated by neutron activation analysis . Appl. Radiat. Isot . 70 , 81 - 87 ( 2012 ). doi: 10.1016/j.apradiso.2011.08.021 http://doi.org/10.1016/j.apradiso.2011.08.021 Trace elements of normal, benign hypertrophic and cancerous tissues of the human prostate gland investigated by neutron activation analysis S. Zaichick , V. Zaichick . Neutron activation analysis of Ca, Cl, Mg, Na, and P content in human bone affected by osteomyelitis or osteogenic sarcoma . J. Radioanal. Nucl. Chem . 293 ( 1 ), 241 - 246 ( 2012 ). Neutron activation analysis of Ca, Cl, Mg, Na, and P content in human bone affected by osteomyelitis or osteogenic sarcoma S. Zaichick , V. Zaichick . EDXRF determination of trace element contents in cancerous tissues of human prostate . In: Fundamental Interactions and Neutrons, Neutron Spectroscopy, Nuclear Structure, Related Topics . Join Institute Nuclear Research , Dubna , 303 - 309 ( 2013 ). EDXRF determination of trace element contents in cancerous tissues of human prostate V. Zaichick , S. Zaichick . The Ca, Cl, Mg, Na, and P mass fractions in human bone affected by Ewing’s sarcoma . Biol. Trace Elem. Res . 159 ( 1-3 ), 32 - 38 ( 2014 ). doi: 10.1007/s12011-014-9966-y http://doi.org/10.1007/s12011-014-9966-y The Ca, Cl, Mg, Na, and P mass fractions in human bone affected by Ewing’s sarcoma V. Zaichick , S. Zaichick , G. Davydov , T. Epatova . The Ca, Cl, Mg, Na, and P mass fractions in benign and malignant giant cell tumors of bone investigated by neutron activation analysis . J. Radioanal. Nucl. Chem . 304 ( 3 ), 1313 - 1320 ( 2015 ). The Ca, Cl, Mg, Na, and P mass fractions in benign and malignant giant cell tumors of bone investigated by neutron activation analysis V. Zaichick , S. Zaichick . The silver, cobalt, chromium, iron, mercury, rubidium, antimony, selenium and zinc contents in human bone affected by Ewing's sarcoma . Journal of Cancer and Tumor International 2 ( 1 ), 21 - 31 ( 2015 ). doi: 10.9734/JCTI/2015/17464 http://doi.org/10.9734/JCTI/2015/17464 The silver, cobalt, chromium, iron, mercury, rubidium, antimony, selenium and zinc contents in human bone affected by Ewing's sarcoma S. Zaichick , V. Zaichick . The content of silver, cobalt, chromium, iron, mercury, rubidium, antimony, selenium, and zinc in osteogenic sarcoma . Journal of Cancer Therapy 6 ( 6 ), 493 - 503 ( 2015 ). doi: 10.4236/jct.2015.66053 http://doi.org/10.4236/jct.2015.66053 The content of silver, cobalt, chromium, iron, mercury, rubidium, antimony, selenium, and zinc in osteogenic sarcoma V. Zaichick , S. Zaichick . The silver, cobalt, chromium, iron, mercury, rubidium, antimony, selenium, and zinc contents in human bone affected by chondrosarcoma . Journal of Hematology and Oncology Research 1 ( 4 ), 25 - 36 ( 2015 ). doi: 10.14302/issn.2372-6601.jhor-15-666 http://doi.org/10.14302/issn.2372-6601.jhor-15-666 The silver, cobalt, chromium, iron, mercury, rubidium, antimony, selenium, and zinc contents in human bone affected by chondrosarcoma V. Zaichick , S. Zaichick . Trace element contents in adenocarcinoma of human prostate investigated by energy dispersive X-ray fluorescent analysis . Journal of Adenocarcinoma 1 ( 1 ), 1 - 7 ( 2016 ). http://adenocarcinoma.imedpub.com/trace-element-contents-in-adenocarcinomaof-human-prostate-investigated-by-energydispersive-xray-fluorescent-analysis.pdf http://adenocarcinoma.imedpub.com/trace-element-contents-in-adenocarcinomaof-human-prostate-investigated-by-energydispersive-xray-fluorescent-analysis.pdf Trace element contents in adenocarcinoma of human prostate investigated by energy dispersive X-ray fluorescent analysis V. Zaichick . Applications of synthetic reference materials in the medical Radiological Research Centre . Fresenius J. Anal. Chem 352 , 219 - 223 ( 1995 ). http://link.springer.com/article/10.1007%2FBF00322330# http://link.springer.com/article/10.1007%2FBF00322330# Applications of synthetic reference materials in the medical Radiological Research Centre R.I. Plotnikov , G.A. Pshenichny . Fluorescent X-ray radiometric analysis , Atomizdat, Moscow ( 1973 ). Fluorescent X-ray radiometric analysis V.P. Afonin , N.I. Komyak , V.P. Nikolaev , R.I. Plotnikov . X-ray fluorescent analysis , Nauka, Novosibirsk ( 1991 ). X-ray fluorescent analysis R.A. Moore , M.L. Miller , A. Mc Lellan . The chemical composition of prostatic secretion in relation to benign hypertrophy of the prostate . J. Urol . 46 , 132 - 137 ( 1941 ). The chemical composition of prostatic secretion in relation to benign hypertrophy of the prostate C. Huggins , W.W. Scott , J.H. Heinen . Chemical composition of human semen and of the secretion of the prostate and seminal vesicles . Amer. J. Physiol . 136 ( 3 ), 467 - 473 ( 1942 ). Chemical composition of human semen and of the secretion of the prostate and seminal vesicles Z.T. Homonnai , H. Matzkin , N. Fainman , G. Paz , P.F. Kraicer . The cation composition of the seminal plasma and prostatic fluid and its correlation to semen quality . Fertil. Steril . 29 ( 5 ), 539 - 542 ( 1978 ). http://europepmc.org/abstract/med/27390 http://europepmc.org/abstract/med/27390 The cation composition of the seminal plasma and prostatic fluid and its correlation to semen quality J.P. Kavanagh , C. Darby . The interrelationships between acid phosphatase, aminopeptidase, diamine oxidase, citric acid, β-glucuronidase, pH and zinc in human prostate fluid . Int. J. Androl . 5 ( 5 ), 503 - 512 ( 1982 ). doi: 10.1111/j.1365-2605.1982.tb00282.x http://doi.org/10.1111/j.1365-2605.1982.tb00282.x The interrelationships between acid phosphatase, aminopeptidase, diamine oxidase, citric acid, β-glucuronidase, pH and zinc in human prostate fluid J.P. Kavanagh . Sodium, potassium, calcium, magnesium, zinc, citrate and chloride content of human prostatic and seminal fluido . J. Reprod. Fertil . 75 ( 1 ), 35 - 41 ( 1985 ). http://www.ncbi.nlm.nih.gov/pubmed/4032375 http://www.ncbi.nlm.nih.gov/pubmed/4032375 Sodium, potassium, calcium, magnesium, zinc, citrate and chloride content of human prostatic and seminal fluido I. Romics , D. Bach . Zn, Ca and Na levels in the prostatic secretion of patients with prostatic adenoma . Int. Urol. Nephrol . 23 ( 1 ), 45 - 49 ( 1991 ). doi: 10.1007/BF02549727 http://doi.org/10.1007/BF02549727 Zn, Ca and Na levels in the prostatic secretion of patients with prostatic adenoma Z.-N. Mo , W.-H. Huang , J. Chen et al . Early and late long-term effects of vasectomy on Zn, Cd, and Cu levels in prostatic fluid and serum . Asian J. Androl . 2 , 121 - 124 ( 2000 ). http://www.ncbi.nlm.nih.gov/pubmed/7500459 http://www.ncbi.nlm.nih.gov/pubmed/7500459 Early and late long-term effects of vasectomy on Zn, Cd, and Cu levels in prostatic fluid and serum O.S. Marenkov , N.I. Komyak , Photon coefficients of interactions for X-ray radiometric analysis, Energoatomizdat, Leningrad ( 1988 ). Photon coefficients of interactions for X-ray radiometric analysis, Energoatomizdat, Leningrad M.H. Burgos . Biochemical and functional properties related to sperm metabolism and fertility . In: Male accessory sex organs (Ed.: Brandes D. ) Academic press , New York , 151 - 160 ( 1974 ). Biochemical and functional properties related to sperm metabolism and fertility Y. Gómes , F. Arocha , F. Espinoza et al . Niveles de zinc en líquido prostático de pacientes con patologías de próstata . Invest. Clin . 48 ( 3 ), 287 - 294 ( 2007 ). http://www.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0535-51332007000300003 http://www.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0535-51332007000300003 Niveles de zinc en líquido prostático de pacientes con patologías de próstata A. Leonov , V. Zaichick . A choice of optimum geometric parameters for the source-sample-detector system using X-ray fluorescent analysis with Si(Li) detector and 109Cd . Voprosy atomnoy nauki i tekhniki. Series: Joint and Nuclear Physics (Kharkov) 2 ( 8 ), 70 - 73 ( 1979 ). A choice of optimum geometric parameters for the source-sample-detector system using X-ray fluorescent analysis with Si(Li) detector and 109Cd X. Fuentes-Arderiu , C.G. Fraser . Analytical goals for the interference . Ann. Clin. Biochem . 28 , 393 - 395 ( 1991 ). http://acb.sagepub.com/content/28/4/393.abstract http://acb.sagepub.com/content/28/4/393.abstract Analytical goals for the interference C.G. Fraser . Biological variation: from principles to practice , AACC Press ( 2001 ). https://www.amazon.com/Biological-Variation-Principles-Callum-Fraser/dp/1890883492 https://www.amazon.com/Biological-Variation-Principles-Callum-Fraser/dp/1890883492 Biological variation: from principles to practice V. Zaichick . Medical elementology as a new scientific discipline . J. Radioanal. Nucl. Chem . 269 , 303 - 309 ( 2006 ). doi: 10.1007/s10967-006-0383-3 http://doi.org/10.1007/s10967-006-0383-3 Medical elementology as a new scientific discipline V. Zaichick . Sampling, sample storage and preparation of biomaterials for INAA in clinical medicine, occupational and environmental health . In: Harmonization of Health-Related Environmental Measurements Using Nuclear and Isotopic Techniques . International Atomic Energy Agency , Vienna 123 - 133 ( 1997 ). https://inis.iaea.org/search/search.aspx?orig_q=RN:29019688 https://inis.iaea.org/search/search.aspx?orig_q=RN:29019688 Sampling, sample storage and preparation of biomaterials for INAA in clinical medicine, occupational and environmental health V. Zaichick . Losses of chemical elements in biological samples under the dry ashing process . Trace Elements in Medicine 5 ( 3 ), 17 - 22 ( 2004 ). http://journal.microelements.ru/microelements_of_midicine/2004_3/17-22.pdf http://journal.microelements.ru/microelements_of_midicine/2004_3/17-22.pdf Losses of chemical elements in biological samples under the dry ashing process The authors are grateful to Dr. Tatyana Sviridova, Medical Radiological Research Center for supplying prostate fluid samples. 10.1007/s41365-016-0133-3 2016-05-30 2016-07-11 2016-07-24 2016-10-12 2016-12-20 2021-04-11 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2016 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-016-0133-3 http://dx.doi.org/10.1007/s41365-016-0133-3 . 2016 Nuclear Science and Techniques 06 27