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<p>The zinc chloride back-titration procedure in GB 1886.229–2016 converts total aluminum to alum content (reported as anhydrous AlK(SO<sub>4</sub>)<sub>2</sub> on a dry basis) without measuring potassium and therefore lacks an internal Al–K stoichiometric check, potentially missing adulteration-related inconsistencies (e.g., substitution with sodium/ferric alum or addition of potassium salts). Al and K were simultaneously quantified by ICP-MS. Alum content was independently calculated from Al and from K (as anhydrous AlK(SO<sub>4</sub>)<sub>2</sub>, dry basis), and their agreement was assessed by both the K/Al molar ratio and a relative deviation metric (Δ =|<i>C</i><sub>K</sub>—<i>C</i><sub>Al</sub>|/((<i>C</i><sub>K</sub> + <i>C</i><sub>Al</sub>)/2) × 100%). Decision rules were pre-defined (<i>R</i> = K/Al molar ratio; Δ agreement metric) to classify stoichiometrically consistent vs. K-deficient or Al-deficient patterns and to select the appropriate conversion channel. The workflow showed good linearity (<i>r</i> &gt; 0.9997), good precision (RSD &lt; 8%), and satisfactory spike recoveries (99.6–107.8%). It enabled rapid screening and corrected quantification in typical adulteration scenarios, whereas the Al-only conversion in the national standard could substantially overestimate alum content under Al-rich substitution. Market samples and simulated adulteration mixtures were used to demonstrate screening sensitivity and quantification correction compared with GB 1886.229–2016. By operationalizing Al-K dual-element stoichiometric screening (K/Al and Δ-based agreement) and applying correction-based quantification for abnormal samples, this practical workflow addresses the analytical blind spot of Al-only conversion and provides a robust solution for routine quality control and regulatory surveillance of food additive alum.</p>

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A Dual-Element Stoichiometric-Consistency Workflow Using Simultaneous Al and K Measurement for Reliable Alum Assay and Adulteration Screening

  • 期刊论文

  • 发表日期：

    2026年4月1日

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  • Zhiji Chen,
  • Li Wang,
  • Micong Jin

摘要

The zinc chloride back-titration procedure in GB 1886.229–2016 converts total aluminum to alum content (reported as anhydrous AlK(SO4)2 on a dry basis) without measuring potassium and therefore lacks an internal Al–K stoichiometric check, potentially missing adulteration-related inconsistencies (e.g., substitution with sodium/ferric alum or addition of potassium salts). Al and K were simultaneously quantified by ICP-MS. Alum content was independently calculated from Al and from K (as anhydrous AlK(SO4)2, dry basis), and their agreement was assessed by both the K/Al molar ratio and a relative deviation metric (Δ =|CK—CAl|/((CK + CAl)/2) × 100%). Decision rules were pre-defined (R = K/Al molar ratio; Δ agreement metric) to classify stoichiometrically consistent vs. K-deficient or Al-deficient patterns and to select the appropriate conversion channel. The workflow showed good linearity (r > 0.9997), good precision (RSD < 8%), and satisfactory spike recoveries (99.6–107.8%). It enabled rapid screening and corrected quantification in typical adulteration scenarios, whereas the Al-only conversion in the national standard could substantially overestimate alum content under Al-rich substitution. Market samples and simulated adulteration mixtures were used to demonstrate screening sensitivity and quantification correction compared with GB 1886.229–2016. By operationalizing Al-K dual-element stoichiometric screening (K/Al and Δ-based agreement) and applying correction-based quantification for abnormal samples, this practical workflow addresses the analytical blind spot of Al-only conversion and provides a robust solution for routine quality control and regulatory surveillance of food additive alum.