Organotin Compound Testing

Organotin compound testing mainly conducts scientific testing and analysis on tributyltin, triphenyltin, monomethyltin, dimethyltin and trimethyltin, monooctyltin and dioctyltin, and mixed organotin compounds, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Tributyltin (TBT) and its derivatives: Tributyltin is one of the most widely used and most toxic organotin compounds, and was once widely used as the active ingredient of antifouling paints for ships. Its testing items usually include TBT itself and its degradation products, such as dibutyltin (DBT) and monobutyltin (MBT), to evaluate its environmental fate and ecological risks.

Triphenyltin (TPT) and its derivatives: Triphenyltin compounds are mainly used as agricultural fungicides and industrial mildew inhibitors. During testing, TPT and its degradation products diphenyltin (DPhT) and monophenyltin (MPhT) need to be paid attention to at the same time, especially in agricultural products, wood products and water environment samples where monitoring is needed as a priority.

Monomethyltin, dimethyltin and trimethyltin: Methyltin compounds mainly come from the decomposition and release of PVC plastic heat stabilizers, and also exist in some industrial wastewater. They have neurotoxicity. During testing, the three different alkylated forms need to be separately quantified, to accurately evaluate their toxic equivalent.

Monooctyltin and dioctyltin: Octyltin compounds are common heat stabilizers in PVC products. The testing focus is on monitoring their migration from plastic products, especially the application safety in fields such as food-contact materials, children's toys and medical supplies.

Mixed organotin compounds: In actual environmental media or commodities, mixtures of multiple organotin compounds often exist. The testing items need to be designed to simultaneously screen and quantify multiple target substances, including compounds with different alkyl chain lengths (such as propyl and cyclohexyl) and different numbers of substituents.

Testing Scope

Environmental water bodies and sediments: The water bodies and sediments of ports, docks, waterways and coastal waters are the key monitoring areas for organotin pollution, mainly testing the antifouling paint residues such as TBT and TPT. Freshwater environments such as rivers and lakes also need to monitor the organotins from agricultural and industrial discharges.

Food and agricultural products: Aquatic products (such as fish, shellfish and crustaceans) are the testing focus due to their bioaccumulation, and the residues such as TBT and TPT need to be monitored. In addition, grains, fruits and vegetables may also need testing due to the use of tin-containing pesticides or soil contamination, and the relevant food safety standards have strict limits for this.

Daily consumer goods and food-contact materials: Including food packaging bags, water pipes and sealing gaskets made of PVC, as well as textiles, leather products and cosmetics (as preservatives). The purpose of the testing is to evaluate the migration risk of organotin stabilizers or additives to food or the human body.

Industrial products and waste: Quality control and compliance testing are carried out on products such as ship antifouling paints, wood preservatives, industrial catalysts and PVC resins. At the same time, wastes such as industrial wastewater and sludge are monitored to prevent pollutants from entering the environment.

Biological tissues and human biomonitoring: The bioaccumulation effect in the ecological chain is evaluated by testing animal tissues (such as whale blubber and liver). In occupational health and epidemiological investigations, human blood and urine are also tested to evaluate the exposure levels.

Testing Methods

Gas chromatography-mass spectrometry (GC-MS): This is the classic method for detecting organotin compounds. After the derivatization treatment of the sample, it is separated by GC, and qualitative and quantitative analysis is carried out by MS. This method has high sensitivity and good selectivity, and can simultaneously analyse multiple organotin species. It is the core technology of the international and domestic standard methods (such as ISO, EPA and GB).

Liquid chromatography-mass spectrometry (LC-MS/MS): Particularly suitable for thermally unstable or strongly polar organotin compounds, without the derivatization step, simplifying the pretreatment. The highly selective reaction monitoring mode can effectively reduce matrix interference, and has obvious advantages in the analysis of complex matrices (such as biological tissues and food).

Inductively coupled plasma mass spectrometry (ICP-MS): As an element-specific detection method, it is often combined with chromatographic separation techniques, such as GC-ICP-MS or HPLC-ICP-MS. This method quantifies by detecting the tin element (¹¹⁸Sn, ¹²⁰Sn), with extremely high sensitivity and a wide linear range, and is a powerful tool for speciation analysis.

Atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry (AFS): Usually used as detectors after chromatographic separation, i.e., combined techniques (such as GC-AAS). Although the sensitivity may be lower than that of MS methods, the equipment is relatively common, and it is still applied in specific laboratories, especially suitable for the determination of specific organotins in relatively simple matrices such as water bodies.

Derivatization technology: This is the key pretreatment step of the GC analysis method. Common derivatization reagents include sodium tetraethylborate (NaBEt₄) and Grignard reagents. Derivatization converts the ionic organotins into volatile alkylated derivatives, thereby improving their separation efficiency and detection sensitivity on GC.

Testing Standards

Domestic Standards:

1. GB/T 20385-2006, Textiles — Determination of organotin compounds

International Standards:

1. ISO 23161:2018, Water quality — Determination of selected organotin compounds — Gas chromatographic method

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Gas chromatography-triple quadrupole mass spectrometer (GC-MS/MS): The mainstream equipment for the current trace detection of organotins. Its triple quadrupole structure can realize accurate quantification of the target substances under complex background interference through the multiple reaction monitoring mode, and the detection limit can reach ng/L (ppt) or even lower, meeting the most stringent regulatory requirements.

Liquid chromatography-tandem mass spectrometer (LC-MS/MS): Equipped with an electrospray ionization source (ESI) or atmospheric pressure chemical ionization source (APCI). It is suitable for the direct analysis of polar organotins and their metabolites, avoiding the errors that may be caused by incomplete derivatization in the GC method, and is increasingly popular in biological sample and food analysis laboratories.

Gas chromatography-inductively coupled plasma mass spectrometer (GC-ICP-MS): The cutting-edge equipment in the field of speciation analysis. GC realizes the separation of compounds, and ICP-MS, as an element-specific detector, is almost free of matrix interference, with an extremely low detection limit and extremely high specificity for tin element detection. It is the first choice for the value assignment of reference materials and cutting-edge research.

Fully automatic sample pretreatment platform: Including automatic solid-phase extraction instruments, microwave digestion/extraction systems and automatic derivatization equipment. They are used to realize the automation and standardization of sample extraction, purification and derivatization, greatly improving the pretreatment efficiency and reproducibility, and reducing human errors and solvent exposure.

Auxiliary equipment and consumables: The key auxiliary equipment includes high-speed centrifuges, nitrogen blowing concentrators and ultrasonic extraction instruments. The dedicated consumables such as C18, HLB and SAX solid-phase extraction cartridges are used for sample purification; and low-polarity chromatographic columns such as DB-5MS and HP-1 are used for GC separation. Reference materials and isotope-labelled internal standards (such as ¹¹⁸Sn-labelled TBT) are crucial for ensuring the quantitative accuracy.