Verifying the feasibility of using Hand-Held X-ray fluorescence 1 spectrometer to identify the origin of Linqing brick: evaluation of the 2 influencing factors, assessing reliability, and providing scientific 3 advice 4

: 23 Linqing brick is quite popular in Chinese history. In 2008, “The manufacturing 24 process of Linqing brick” was selected as the intangible cultural heritage list in China. 25 Currently, identifying the origin of Linqing brick represents an important issue to be 26 investigated in the field of archeology and architectural history research in China, as it 27 could be used to verify certain assumptions regarding the history of heritage buildings, 28 the resolution for which cannot be obtained by examining the historical documents. 29 Hand Held enables the in-situ determination of the main elements and concentrations of Linqing brick in a rapid non-destructive manner. HH-XRF may prove to be significant in identifying the origin of Linqing brick. However, HH-XRF could be influenced by certain factors and may be capable of measuring only the element concentrations of the surface for the brick in situ. Which method would provide the most reliable data is an important concern. The aim of the present study was to verify the reliability of HH-XRF and to systematically evaluate the different factors influencing measurement precision and accuracy, in order to assist with scientific advice for the usage of HH-XRF. Four experiments were performed to determine the influencing factors and to assess reliability through cross-validation using inductively coupled plasma optical emission spectrometry (ICP-OES). Finally, the reliability of HH-XRF was ensured, and the scientific advice regarding its application in determining the concentrations of the main elements of Linqing brick was provided.


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Linqing brick is quite popular in Chinese history. Several architectural heritages 68 have been built mainly by using Linqing brick, such as the Forbidden City, the 69 Temple of Heaven, Ming Tombs, Eastern Qing Tombs, and Western Qing Tombs. In  [8,9]. 95 HH-XRF has also been used in combination with other scientific instruments, 96 such as diffuse reflectance infrared Fourier transform and Raman spectrometers, in 97 order to examine the building materials (e.g., bricks) for studying the diseases of 98 buildings. Some scholars focused on estimating the impact suffered by the building 99 materials and studying the degradation processes for the heritage buildings close to 100 coastal areas [10,11] The instrument used in the present study was Niton XL2-960 GOLDD XRF 123 Analyzer equipped with an Ag anode operating at a maximum of 45 kV and 100 uA.

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The spot size of the emitted X-Ray beam was 8 mm. 126 Twenty bricks were used as samples (Table S1). In experiment 1 and experiment 127 2, only brick 4 was used. In experiment 3 and cross-validation, all the bricks were 128 used. The main elements studied in the present research were Fe, Ca, K, Al, and Si, 129 the elements with concentrations higher than 1%. However, in order to determine 130 whether HH-XRF could measure all the elements, in experiment 1, the elements with 131 a concentration higher than 0.1% were studied (Fe, Ca, K, Al, Si, Ba, Zr, Mn, Mg, Ti, 132 7 and Cl). The elements studied in experiment 2, experiment 3, and cross-validation (Fe, 133 Ca, K, Al, and Si) were the main elements of the present research. EPA criteria were used to evaluate data quality (Table 1).  The measurements were performed at 10 time points: prior to the rain, and 0, 1, 2, 147 3, 5, 7, 9, and 12 h after rain. The measurement conditions were as follows: rainfall      Three fresh sections were cut for each brick that was subjected to measurements.

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The mean elemental concentrations of these three sections were compared with the  The bricks were cut into small pieces, and each brick sample was subsequently 175 ground into a fine powder with particle diameter less than 150 µm. Next, total 9 microwave digestion was used to digest the sample. The digested sample (500 mg) 177 was placed in a PTFE reactor with 4 mL HNO 3 (70%), 1 mL H 2 O 2 (20%), and 2 178 mL HF (40%). When the foam caused by the decomposition of organic matter 179 disappeared, the container was capped and heated using a microwave digestion   The data generated using HH-XRF were assessed using established criteria 194 through cross-validation ( Table 1). The RSD, R², and inferential statistics were used 195 to assess a data quality level comparable to the relationship between HH-XRF and 196 ICP-OES.

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For the linearity level , if the coefficient of determination (R²) obtained in the 198 10 linear regression analysis between HH-XRF and the validation method was greater 199 than 0.7, a Q2 quality level would be achieved. In order to achieve a Q3 quality level, 200 R² must be greater than 0.85 (Table 1).

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In regard to precision requirements, if RSD ≤ 10%, a Q3 quality level is 202 achieved. In addition, RSD = 20% serves as the threshold between the Q2 and Q1 203 quality levels. RSD is calculated by dividing the size of residual standard error by the 204 mean (Table 1). 205 In regard to inferential statistics, only the gradient of the line is close to 1, and 206 the y-intercept is approximately 0, indicating a Q3 quality level, implying statistical 207 similarity (Table 1).

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The present study demonstrated that an optimal measurement time is strongly 237 dependent on the element under investigation (Fig. 1). In the case of Fe, Ca, K, Al, 238 and Si, the main research elements of the present study, RSD was less than 5% for 239 each measurement time (Fig. 1a). In the case of Ba, Zr, and Mn, RSD was less than 10% 240 for each measurement time (Fig. 1b). Therefore, it is suggested that 60 s should be 241 selected as the measurement time for Fe, Ca, K, Al, Si, Ba, Zr, and Mn (Table 2).

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However, for Mg, RSD was 64.93% when 60 s was selected as the measurement time.

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The RSD value obviously decreased from 64.93% for 60 s to 11.42% for 180 s. This 244 rule was also applicable to Ti (Fig. 1c). Therefore, it is suggested that 180 s be 245 selected as the measurement time for Mg and Ti (Table 2). In the case of Cl, RSD 246 values fluctuated, covering a wide range; at certain times, the values were larger than 247 30%, while at other times, the values were smaller than 5%, without exhibiting any 248 relationship with the corresponding measurement time (Fig. 1d). Therefore, it was 249 inferred that using a Niton XL2-960 GOLDD XRF Analyzer to measure Cl in a

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Linqing brick is inappropriate.   The present study demonstrated that all the investigated elements, with the only 268 exception of K, are greatly influenced by rain, and that it takes a long time for the 269 concentrations of these elements to return to the pre-rain values (Fig. 2). In the present  The bricks on the exterior wall of the ancient buildings have been exposed to the   (Table S2-S6). Interestingly, the differences between the maximum and minimum 308 concentrations within 10 points were under 0.4% for almost all the bricks investigated 309 for elements Fe, K, and Al, while for Si, the differences were under 1%. Only a few 310 points did not satisfy this condition, such as point 1 in brick 1 for K (Table S4); these 311 specific values should be ignored as exceptions. In regard to Ca, certain cases are 312 similar to those for Fe, K, and Al, while in other cases, the concentration difference 313 between points is huge (Table S3), which might be led by the concentration 314 distributions for the bricks itself. Therefore, if this phenomenon occurs, the value 315 measured for this element of this brick should be discarded.

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In order to ensure the accuracy of the measurements, 10 points must be selected   It is clear that the value differences between the sections and the points were not 332 much large for most cases. However, for K and Ca, there were a few cases that 333 exhibited large differences between the sections and the points (Table S7). The main 334 reason for this was that Ca and K were greatly affected by crystalline bloom, while the 335 elements Fe, Al, and Si were affected less by this phenomenon.

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18 In regard to this phenomenon, it would be better to select a brick located on a 337 higher position in the wall. In comparison to the bricks close to the ground, capillary 338 suction of the wall at a higher position is much smaller. Therefore, crystalline bloom 339 at a higher position would be lighter, leading to a lesser impact on K and Ca.

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Meanwhile, if conditions permit, it is better to select the bricks inside a room of the 341 ancient building for the measurements. phases [23]. In this context, total microwave acid digestion, which is suitable for 359 organic-rich and silicate-containing media with proven recoveries approaching 100%, 360 was used in the present study to ensure maximum comparability between the 361 HH-XRF and ICP data.

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In order to verify the reliability of the HH-XRF results in the present study, 363 correlation regression analysis was performed between the concentration values 364 measured using ICP-OES and those measured using HH-XRF (Fig. 3). In case of Fe, 365 Al, and Si elements, all the 20 bricks were used, while for K and Ca, 16 and 12 bricks 366 were used, respectively, after removing certain cases in which either the surface was 367 not uniform or the difference between the surface and the interior was huge.

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In the case of Fe, Al, and Si, the coefficient of determination was greater than 369 0.85, implying that a Q3 quality level was achieved ( Fig. 3a and 3c-3d). In the case of 370 K, a Q2 quality level was achieved (Fig. 3b). All these four elements fulfilled the 371 precision requirements for Q3 level (<10% RSD). In addition, for the inferential 372 statistics (gradient and intercept), all these four models fulfilled the requirements for a 373 Q2 quality level, i.e., the relationship y = mx or y = mx + c was accepted.

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In the case of Ca, even after removing certain values as stated in 3.3.1 and 3.3.2, 375 the R² for this element reached only 0.61. Therefore, the reliability of HH-XRF for Ca 376 was not satisfactory (Fig. 3e).

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In the case of Fe, K, Al, and Si, the value obtained using ICP-OES was used to

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It was concluded that HH-XRF is a reliable instrument for the in-situ