Solutions work best when combined with ionic strength and pH adjustors, which eliminate interferences from other ion species and adjust standards and samples to an optimal pH range. All standardizing solutions and ionic strength adjustors come in 475-ml bottles except model 05730-15, (1 gal), and model 05730-53, (five 50-ml bottles). All filling solutions for reference electrodes come in cartons of one or five 50-ml bottles.