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N/10 HCl (Hydrochloric Acid Solution) supplied by laboratory distributors like IBEX SCIENCES is a standardized volumetric reagent. The designation “N/10” denotes a Normality of 1/10 (or 0.1 N). [1, 2, 3]
Because hydrochloric acid is a monoprotic mineral acid (releasing exactly one hydrogen ion per molecule), its normality is equivalent to its molarity (0.1 M). It contains precisely 3.646 grams of pure hydrogen chloride gas dissolved per liter of purified water. [1, 2, 3, 4]
In medical diagnostic and pathology laboratories across Pakistan, its most prominent and critical application is serving as the primary reacting reagent for the manual visual estimation of hemoglobin using Sahli’s Method (also known as the Acid Hematin Method). [1, 2]
Core Diagnostic Principle (Sahli’s Method)
The reagent acts directly on the iron-bearing proteins in a blood sample to produce a measurable color change: [1]
- Acid Hematin Conversion: When fresh, anticoagulated whole blood is mixed with N/10 HCl, the acid lyses the red blood cells and chemically alters the released hemoglobin molecules. [1, 2]
- Color Presentation: This reaction converts the hemoglobin into acid hematin, a distinct, stable brown compound. The intensity of this brown color is directly proportional to the concentration of hemoglobin present in the patient’s blood. [1, 2, 3, 4]
Standard Manual Laboratory Procedure
Technicians strictly utilize the solution within a graduated Sahli hemoglobinometer kit according to a precise timing cycle: [1]
- Initial Dispensing: Add the N/10 HCl Solution into the specialized graduated Sahli tube exactly up to the lowest marked boundary (typically marked as 2 g% or the 10% line). [1, 2]
- Blood Addition: Using a precise Sahli pipette, draw exactly 20 µL (0.02 mL) of whole blood. Wipe the outside of the pipette tip and expel the blood sample directly into the acid layer. Rinse the pipette by drawing the acid mixture up and down twice. [1]
- Incubation: Mix the solution gently using a thin glass stirrer and let the tube rest undisturbed at room temperature for exactly 10 minutes. This delay is critical because the dark brown acid hematin complex develops slowly, reaching its maximum color saturation at the 10-minute threshold. [1, 2]
- Dilution & Color Matching: Place the tube inside the Sahli comparator box alongside the built-in tinted glass color standards. Add distilled water drop-by-drop, stirring after each addition, until the brown color of the solution perfectly matches the tone of the reference glass rods. [1]
- Result Reading: Read the level of the lower liquid meniscus directly from the graduated scale on the tube to find the hemoglobin result expressed in grams per deciliter (g/dL or \(\text{g\%}\)). [1, 2]
Key Storage & Analytical Workbench Guidelines
- Strict Volumetric Accuracy: Dispensing less than the required amount of N/10 HCl can lead to incomplete conversion of hemoglobin or sample clotting. Conversely, adding too much acid initially can cause an overly faint reaction from the start, making accurate comparison impossible for anemic patients. [1]
- Carbon Dioxide Protection: Keep the container tightly capped when not in use. Prolonged exposure to ambient air can result in evaporation or small fluctuations in stability, which can alter titration accuracy over time. [1]
- Safety Handling Profile: While a 0.1 N concentration is highly diluted and considerably safer to manage than concentrated mineral acids, it retains a low pH (< 2). It remains a mild irritant to skin and mucous membranes. Technicians must wear appropriate laboratory personal protective equipment (PPE)—including lab coats, gloves, and protective eyewear—during testing. [1, 2, 3, 4, 5]
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