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Introduction of a spectrophotometric method for salivary iodine determination on microplate based on Sandell-Kolthoff reaction

Adrijana Oblak

Adrijana Oblak

  • Division of Nuclear Medicine, University Medical Centre LjubljanaLjubljana, Slovenia
  • Faculty of Medicine, University of LjubljanaLjubljana, Slovenia
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Oblak, Adrijana
, 
Jernej Imperl

Jernej Imperl

Faculty of Chemistry and Chemical Technology, University of LjubljanaLjubljana, Slovenia
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Imperl, Jernej
, 
Mitja Kolar

Mitja Kolar

Faculty of Chemistry and Chemical Technology, University of LjubljanaLjubljana, Slovenia
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Kolar, Mitja
, 
Gregor Marolt

Gregor Marolt

Faculty of Chemistry and Chemical Technology, University of LjubljanaLjubljana, Slovenia
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Marolt, Gregor
, 
Blaz Krhin

Blaz Krhin

Division of Nuclear Medicine, University Medical Centre LjubljanaLjubljana, Slovenia
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Krhin, Blaz
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Katja Zaletel

Katja Zaletel

  • Division of Nuclear Medicine, University Medical Centre LjubljanaLjubljana, Slovenia
  • Faculty of Medicine, University of LjubljanaLjubljana, Slovenia
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Zaletel, Katja
 and 
Simona Gaberscek

Simona Gaberscek

  • Division of Nuclear Medicine, University Medical Centre LjubljanaLjubljana, Slovenia
  • Faculty of Medicine, University of LjubljanaLjubljana, Slovenia
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Gaberscek, Simona
  
Jul 22, 2024
Introduction of a spectrophotometric method for salivary iodine determination on microplate based on Sandell-Kolthoff reaction's Cover Image
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Article Category: Research Article
Published Online: Jul 22, 2024
Page range: 357 - 365
Received: Apr 16, 2024
Accepted: May 28, 2024
DOI: https://doi.org/10.2478/raon-2024-0035
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© 2024 Adrijana Oblak et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.

FIGURE 1.

Comparison of measurements of artificial saliva standards (ASS) by two different methods, inductively coupled plasma mass spectrometry (ICP-MS) and Sandell-Kolthoff method (S-K) using ammonium peroxydisulfate on microplate.
Comparison of measurements of artificial saliva standards (ASS) by two different methods, inductively coupled plasma mass spectrometry (ICP-MS) and Sandell-Kolthoff method (S-K) using ammonium peroxydisulfate on microplate.

FIGURE 2.

Comparison of different ammonium peroxydisulfate concentrations and their influence on the determined salivary iodine concentration. Comparison between 0.5 and 1.5 mol/L, as well as between 0.5 and 1.0 mol/L for all three samples showed significantly different values (P<0.001) for all three samples, whereas P values for samples 1, 2, and 3, showed no difference between 1.0 and 1.5 mol/L. The corresponding P values were 0.275, 0.085, and 0.761, respectively.
Comparison of different ammonium peroxydisulfate concentrations and their influence on the determined salivary iodine concentration. Comparison between 0.5 and 1.5 mol/L, as well as between 0.5 and 1.0 mol/L for all three samples showed significantly different values (P<0.001) for all three samples, whereas P values for samples 1, 2, and 3, showed no difference between 1.0 and 1.5 mol/L. The corresponding P values were 0.275, 0.085, and 0.761, respectively.

FIGURE 3.

Comparison of salivary iodine concentration (SLIC) determined by the Sandell-Kolthoff (S-K) method using ammonium peroxydisulfate on microplate and by the Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using Passing-Bablock regression. The solid line shows the regression line, dashed lines show 95% confidence interval (CI) for the regression line, and dotted line shows the identity line Y = X. The sample size is N = 110. The regression equation is Y = 0.89*X+6.2. The slope is 0.89 (95% CI, 0.86−0.92), and the intercept is 6.2 (95% CI, 3.3−8.6). The Cusum test for linearity showed no significant deviation from linearity (P = 0.89).
Comparison of salivary iodine concentration (SLIC) determined by the Sandell-Kolthoff (S-K) method using ammonium peroxydisulfate on microplate and by the Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using Passing-Bablock regression. The solid line shows the regression line, dashed lines show 95% confidence interval (CI) for the regression line, and dotted line shows the identity line Y = X. The sample size is N = 110. The regression equation is Y = 0.89*X+6.2. The slope is 0.89 (95% CI, 0.86−0.92), and the intercept is 6.2 (95% CI, 3.3−8.6). The Cusum test for linearity showed no significant deviation from linearity (P = 0.89).

FIGURE 4.

Bland-Altman plot of comparison of salivary iodine concentration (SLIC) determined by the Sandell-Kolthoff method (S-K) and by the Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Differences between the methods are plotted against the ICP-MS method, which is a gold standard method. Sample size is N = 110. Horizontal lines represent the mean SLIC by ICP-MS, zero difference, and 95% confidence interval limits of agreement, which are defined as mean difference plus/minus 1.96 times the standard deviation (SD) of the differences. The mean shows a positive bias of 5.9%.
Bland-Altman plot of comparison of salivary iodine concentration (SLIC) determined by the Sandell-Kolthoff method (S-K) and by the Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Differences between the methods are plotted against the ICP-MS method, which is a gold standard method. Sample size is N = 110. Horizontal lines represent the mean SLIC by ICP-MS, zero difference, and 95% confidence interval limits of agreement, which are defined as mean difference plus/minus 1.96 times the standard deviation (SD) of the differences. The mean shows a positive bias of 5.9%.

Recoveries of 6 different saliva samples spiked with 19_6, 38_5, 74_1, and 193_5 mg/L of stock solutions of potassium thiocyanate and of caffeine to saliva samples_ Recoveries are expressed as percentages of observed amount of iodine over expected amount of iodine after thiocyanate or caffeine stock solutions added to samples_ Each sample was measured 8 times and results are presented as mean salivary iodine concentration (SLIC) (SD) and as the mean percentage recovery (range) of iodine at each concentration level

Thiocyanate Caffeine
SLIC, μg/L (SD) Recovery, % (range) SLIC, μg/L (SD) Recovery, % (range)
Sample 1 34.7 (3.0) 97.9 (97.3–100.5) 29.1 (1.0) 93.2 (90.7–96.3)
Sample 2 86.0 (7.4) 101.2 (99.0–102.8) 73.0 (1.6) 99.3 (97.0–100.9)
Sample 3 90.7 (3.7) 102.4 (99.0–105.0) 75.2 (1.9) 96.1 (92.0–100.4)
Sample 4 109.0 (3.9) 109.0 (95.9–104.9) 101.3 (3.8) 96.3 (94.1–99.0)
Sample 5 143.0 (2.2) 106.2 (103.8–108.7) 142.1 (2.5) 98.7 (96.1–105.3)
Sample 6 150.6 (3.3) 102.4 (98.2–107.7) 152.8 (3.0) 99.3 (97.3–101.3)

Dilutions of 4 saliva samples with deionised water_ Each sample was measured 8 times and results are presented as mean measured concentration (SD)_ Recoveries are expressed as the percentages of mean measured amount of iodine over expected amount of iodine after dilution

Dilution Measured (M) μg/L (SD) Expected (E) μg/L M/E %
Sample 1 Non-diluted 105.7 (1.3) / /
1:2 56.9 (1.3) 52.9 107.7
1:4 28.8 (2.0) 26.4 109
Sample 2 Non-diluted 35.6 (1.0) / /
1:2 19.2 (1.4) 17.8 108.2
Sample 3 Non-diluted 76.7 (1.3) / /
1:2 40.2 (1.7) 38.4 104.8
1:4 17.3 (1.2) 19.2 90.3
Pooled sample Non-diluted 165.1 (5.4) / /
1:2 65.0 (3.6) 61.9 105.0
1:4 33.8 (1.7) 31.0 109.1
1:8 17.2 (1.6) 15.5 111.1

Coefficients of variation (CV [%]) for intra- and inter-assay for 4 different iodine concentrations for salivary iodine concentration (SLIC)

Level Target value, μg/L Number of measurements Intra-assay imprecision, % Number of measurements Inter-assay imprecision, %
1 20 40 18.4 198 20.7
2 100 40 5.1 192 6.7
3 350 40 2.8 121 4.3
Pooled sample 165 40 5.7 80 5.1
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