Switchable hydrophilicity solvent based and solidification-assisted liquid-phase microextraction combined with GFAAS for quantification of trace soluble lead in raw bovine and derivative milk products

ABSTRACT

A novel microextraction method was developed by combining CO₂-controlled switchable hydrophilicity solvent (SHS) with solidification of the aqueous phase (SAP), referred to as CSHS-SAP. It was applied for pre-concentration/extraction of the complexes of Pb-ammonium pyrrolidine dithiocarbamate (APDC) prior to GFAAS detection in raw bovine milk and milk products (whole-fat, half-skimmed and skimmed milks). In the CSHS-SAP microextraction, a clear interface was easily formed, and convenient and complete collection was achieved by directly transferring the SHS phase into a vial, which overcame the shortcomings of blurred interface and difficult collection of SHS phase using CSHS-based microextraction. SAP led to the increase of extraction recoveries for Pb²⁺ by 8–11%. Some important factors were optimised using a one-factor-at-a-time approach: 800 µL of N,N-dimethylbutylamine and water at a ratio of 1:1 as SHS, 1.0 g L⁻¹ APDC as chelating agent, sample pH = 6.0, 0.6 mL of 1.0 mol L⁻¹ NaOH, solidification time of 70 min and 300 µL of 0.5 mol L⁻¹ HNO₃ for back extraction. Under optimised conditions, limits of detection were as low as 0.01–0.02 µg kg⁻¹ and enrichment factors reached more than 23-fold. Inter- and intra-day precisions had relative standard deviations of 3.6–6.4%. With the CSHS-SAP/GFAAS method Pb²⁺ was detected at 0.5–1.8 µg kg⁻¹ in four bovine raw milk samples, which were collected from Hubei and Henan Provincial oil-producing area, China. However, Pb²⁺ was below the LOD in all of the local milk products. Overall, the newly developed CSHS-SAP/GFAAS method is convenient, efficient and robust, giving it great potential for rapid and accurate analysis of trace Pb²⁺ in liquid milks.

KEYWORDS:

• CSHS-SAP
• switchable hydrophilicity solvent
• lead
• GFAAS
• bovine milk

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This study was jointly funded by the National Natural Science Foundation of China (21876125 and 51608341), Zhejiang Provincial Natural Science Foundation (LY19B070010) and Suzhou City Science and Technology Project (SYG201815, SNG2018047 and SNG2018051).