Patent blue 5 sodium salt

Paracetamol was selected as a representative test compound with characteristics typical of APIs. It is commercially available, as are its impurities of synthesis. Two extremes of size distribution (granular and micronized) were selected to challenge different aspects of filtration, washing, and drying. The granular material (batch 161713J561; Mallinckrodt Inc., Staines-upon-Thames, UK) represents a challenge for uniform particle suspension and transfer into the filter and exhibits very rapid settling and filtration. The micronized material (batch 042213E407; Mallinckrodt Inc.) settles and filters slowly, has a large wetted surface area to wash, and is more challenging to dry than the granular material.
Wash performance and cake purity were evaluated using a solvent soluble dye, Patent Blue V sodium salt (LOT: BCBP1872V; Sigma-Aldrich). The dye aids visualization of the filtration and washing process as well as being readily quantified spectroscopically.
Ethanol (absolute, !99.8%; Sigma-Aldrich) was used to create the feed suspension; it is widely used as crystallization solvent. Millipure water was selected as wash solvent due to paracetamol's relatively low aqueous solubility and because Patent Blue V dye is very soluble in water, as reported by Newton et al. 21

Pepsin (2188 U mg -1 ) from porcine gastric mucosa, α-amylase (1333 U mg -1 ) from Bacillus sp., trypsin from bovine pancreas, Patent Blue V sodium salt, ethylenediaminetetraacetic acid (EDTA), disodium salt dihydrate, ascorbic acid, 1,1,3,3-tetraethoxypropane and 2,4-dinitrophenylhydrazine (DNPH) were purchased from Sigma-Aldrich (Stockholm, Sweden). Brij 35 was obtained from Fisher Scientific (Acros Organics, Västra Frölunda, Sweden). Lipase F-AP 15 (150 U mg -1 ) from Rhizopus oryzae was purchased from Amano Enzyme Inc. (Nagoya, Japan). Fresh porcine bile was obtained from TNO (Zeist, The Netherlands). Pancreatin (Pancrex-Vet, Pfizer, Karlsruhe, Germany) was purified by centrifugation (9000g, 20 min, 4 °C) before use. Wheat flour bread containing 1% vegetable oil (0.4% saturated) was bought in a local supermarket. 4-Hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE) were purchased from Cayman Chemicals (Michigan, USA). All other chemicals used were of analytical grade.