Standard for paraquat dichloride technical concentrate active constituent

Effective Date: 
25 January 2011
1. Description: 

The material shall consist of paraquat dichloride together with related manufacturing impurities, in the form of an aqueous solution, free from visible extraneous matter, and must contain an effective emetic (see note 2). The material may also include colorants and olfactory alerting agents.

2. Common Name: 
Paraquat dichloride technical concentrate
3. Chemical Name (IUPAC): 

1,1'-dimethyl-4,4'-bipyridinium dichloride


4. CAS Number: 
1910-42-5 (4685-14-7 dication)
5. Identity test: 
identity of the active constituent must be established by one or more of the following methods: spectroscopic tests (IR spectrum, NMR, mass spectra), Chromatography (HPLC or GC retention time with reference compound) or any other suitable test method.
6. Composition: 

6.1 Active constituent: Paraquat dichloride content shall be declared. The minimum purity on a dry weight basis is 920 g/kg.  Paraquat dichloride manufacturing concentrate shall contain a lower limit of 500 g/L paraquat dichloride, which corresponds nominally to 442 g/kg paraquat dichloride (320 g/kg paraquat ion). When determined, the average measured content shall not differ from that declared by more than ± 25 g/L, which corresponds to ± 5% on a g/kg basis.

6.2 Toxicological Impurities:
Total terpyridines: 0.001 g/kg (1.0 ppm) maximum 
4,4'-bipyridyl: 1.0 g/kg (1000 ppm) maximum

Note 1:
The product must not be allowed to come into direct contact with metal.  If metal is used, containers must be lined with suitable polymeric material, or the internal surfaces treated to prevent corrosion of the container and/or deterioration of the contents.

Note 2:
An effective emetic, having the following characteristics, must be incorporated into the TK.

  • It must be rapidly absorbed (more rapidly than paraquat) and be quick acting. Emesis must occur in about half an hour in at least 50% of cases
  • It must be an effective (strong) stimulant of the emetic centre of the brain, to produce effective emesis. The emetic effect should have a limited ‘action period’, of about two to three hours, to allow effective treatment of poisoning
  • It must act centrally on the emetic centre in the brain
  • It must not be a gastric irritant because, as paraquat is itself an irritant, this could potentiate the toxicity of paraquat
  • It must be toxicologically acceptable. It must have a short half-life in the body (to comply with the need for a limited action period).
  • It must be compatible with, and stable in, the paraquat formulation and not affect the herbicidal efficacy or occupational use of the product

To date, the only compound found to meet these requirements is 2-amino-4,5-dihydro-6-methyl-4-propyl-s-triazole-(1,5a)pyrimidin-5-one (PP796). PP796 must be present in the TK at not less than 0.8 g/l.

7. Analytical methods: 
  • The analytical method used for the determination of the active constituent and toxicological significant impurities must be validated in accordance with the APVMA guidelines for the validation of analytical methods
  • The APVMA guidelines on validation of analytical methods state that 'Analytical methods described in CIPAC handbooks and AOAC International Manual, and in recognized pharmacopoeias [BP, BP (Vet), Ph Eur and USP] for a particular active constituent or formulation are regarded as validated and do not require revalidation'. However, the suitability of these methods must be verified under actual conditions of use ie, the selectivity and accuracy of the method should be demonstrated for the published method when applied to the relevant sample matrix and laboratory conditions.
  • When a CIPAC or AOAC method is used for the assay of an active constituent in a bulk active constituent, there is no matrix. The registrants need to check the specificity of the method to ensure there is no interference from impurities or degradation products. However, determination of accuracy of the method is not required as there is no potential for the product matrix to have an effect on the determination of the active constituent. However, when a CIPAC or AOAC method is used for the assay of an active constituent in a formulated product, determination of both specificity and accuracy is required as the matrix is relevant in formulated products (formulated products have different composition and quantities of excipients).
  • Unless the scope of the collaborative method (CIPAC and AOAC) also includes toxicologically significant impurities in the active constituent, validation data for impurities are required.



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