Which chemical preservation method is required for a sample collected for Total Metals analysis (e.g., Iron or Manganese) to keep the metals dissolved in solution during transport?

• Add Sodium Thiosulfate to remove chlorine
• Store the sample at 35 °C
• Add Nitric Acid (HNO3) to lower the pH to < 2.0
• Add Sodium Hydroxide (NaOH) to raise the pH to > 12.0