ICP-MS determination and uncertainty assessment of eight mineral elements in blackberry fruits at different developmental stages

【Objective】To clarify changes in the mineral composition of blackberry fruits, this study used organically grown blackberries at different maturity stages as raw materials. It compared wet digestion and microwave digestion methods, incorporated uncertainty analysis, and comprehensively evaluated the reliability of the experimental approach. This research would provide technical support for assessing dynamic changes in mineral elements during blackberry ripening.【Methods】Using inductively coupled plasma-mass spectrometry (ICP-MS) with dynamic collision cell mode, this study compared the sealed digestion (SD) and microwave digestion (MD) methods to investigate the dynamic changes in sodium, potassium, calcium, magnesium, copper, iron, zinc, and manganese during blackberry ripening. The following parameters were included: Spiked recovery u1(Sm), pipette u2 (std), internal standard u2 (Sm), mother liquor u1 (std), sample repeatability u2 (Cp), volumetric flask temperature u2 (V), fitting u3 (std), blank solution repeatability u1 (Cp), volumetric flask calibration u1(V), volumetric flask repeatability u3 (V), balance repeatability u2(m), balance calibration u1(m), and instrument u3(Sm).【Results】The correlation coefficients for the standard curves of all 8 elements exceeded 0.999, with spiked recovery rates ranging from 93.33% to 104.50%. This method demonstrated high sensitivity and precision During blackberry development, as the fruits expanded and ripened, the contents of the 8 minerals showed a significant overall downward trend: an initial decline followed by stabilization. From the green fruit stage to the color change stage, the concentrations of all 8 minerals decreased substantially, with the most pronounced changes observed in sodium, potassium, and zinc. During color change stage Ⅱ, the concentrations of sodium, iron, magnesium, calcium, zinc, and manganese increased, while those of potassium and copper decreased. During color change stage Ⅲ, potassium and manganese increased, while the remaining six elements decreased. At maturity, sodium, potassium and manganese decreased, while the other five elements increased to varying degrees. This indicates that all eight elements show a significant downward trend during blackberry fruit coloration, suggesting that substantial physiological changes accompany this process and significantly impact mineral absorption and metabolism. The contents of sodium, potassium, and manganese show the most pronounced decline during fruit ripening, which would provide theoretical support for water and fertilizer management in blackberry cultivation. The uncertainty values for each component during the testing process, sorted from largest to smallest, are as follows: Spiked recovery u1 (Sm) ＞ Pipette u2 (std) ＞ Internal standard u2 (Sm) ＞ Stock solution u1 (std) ＞ Sample repeatability u2 (Cp) ＞ Volumetric flask temperature u2 (V) ＞ Fitting u3 (std) ＞ Blank solution repeatability u1 (Cp) ＞ Volumetric flask calibration u1 (V) ＞ Instrument u3 (Sm). Among the five uncertainty sources, volumetric flask repeatability u3 (Sm) has the highest uncertainty, (V) ＞ volumetric flask repeatability u3 (V) ＞ balance repeatability u2 (m) ＞ balance calibration u1(m) ＞ instrument u3 (Sm). For the other five uncertainty sources, the uncertainty contribution ranks as follows: sample matrix Urel (Sm) ＞ standard curve preparation Urel (std) ＞ sample preparation Urel (Cp) ＞ volume adjustment Urel (V) ＞ weighing Urel (m). This indicates that standard curve preparation and the sample matrix are the dominant contributors to uncertainty in the determination of eight elements in blackberries by inductively coupled plasma mass spectrometry. Among these factors, spiked recovery, pipette usage, internal standards, and standard stock solutions exerted the greatest influence on the test results in this study. The expanded uncertainty coefficients for all 8 elements were below 5%, and in descending order, they are: Calcium ＜ magnesium ＜ potassium ＜ copper ＜ sodium ＜ iron ＜ manganese ＜ zinc. Component analysis revealed that the spiked recovery of manganese and zinc introduced relatively higher uncertainties. The combined uncertainty for the eight elements ranged from 0.011 271 to 0.022 888, with expanded uncertainty percentages as follows: sodium (2.76% ), potassium (2.54% ), calcium (2.25% ), magnesium (2.49%), copper (2.66%), iron (2.89%), zinc (4.58%), and manganese (3.12%).【Conclusion】This study established a microwave digestion- inductively coupled plasma mass spectrometry (ICP- MS) method to determine the contents of eight minerals in blackberries. After validating the method's linearity, detection capability, precision, accuracy, robustness, and measurement uncertainty, this research clarified the variation trends of these eight mineral contents during the fruit development of blackberries. The findings would provide data support and a theoretical basis for further relevant research.