The indicator used is Tashiro's indicator. It is a mixed indicator, namely, a mixture of methylene blue and methyl red.

Request you to search for it through a suitable search engine. 

With best wishes,

ARB

Dear Purkayastha,

Please go through attached link and go further page no. 36.

http://www.isca.co.in/ENVIR_SCI/lab_manual/Hand%20Book%20of%20Water,%20Air%20and%20Soil%20Analysis.pdf

Thank u sir for such an helpful pdf.

Regards,

Debasree

methyl red and methylene blue mixed indicator works better.

tashiro

Tashiros indicator works well

Mixed indicator ( methyl red +methylene blue)

In kejldahl methode for nitrogen content i m getting blue color insted of green in distillation step when i m adding boric aid indicator why? Please suggest me some solution of this problem.

Dear Esteemed Colleague,

Thank you for reaching out with your inquiry regarding the Kjeldahl method, specifically concerning the appropriate indicator to use during the titration step. The Kjeldahl method is a well-established analytical technique for the determination of nitrogen content in organic substances, widely applied in food analysis and environmental studies. The method consists of three primary stages: digestion, neutralization, and titration. The choice of indicator in the titration step is crucial for achieving accurate results.

Indicator Used in the Titration Step of the Kjeldahl Method:

During the titration phase of the Kjeldahl method, the solution's acidity is neutralized, and the amount of acid equivalent to the ammonia (which in turn is equivalent to the nitrogen content) is measured. The most commonly used indicator for this purpose is Bromocresol Green. This choice is due to Bromocresol Green's ability to provide a clear and distinct color change at the pH range encountered at the endpoint of the ammonia titration, which typically occurs around a pH of 4.2 to 5.4.

Why Bromocresol Green?

Bromocresol Green transitions from yellow to blue-green as the pH moves from acidic to slightly alkaline, making it particularly suitable for detecting the endpoint of the titration in the Kjeldahl method. This sharp color change allows for precise determination of the moment when all the ammonia has been neutralized, ensuring the accuracy of the nitrogen content calculation.

Additional Considerations:

• Accuracy of Endpoint Detection: The precision in detecting the titration endpoint can be affected by the sample's color and clarity. It is essential to consider these factors when interpreting the color change.
• Alternative Indicators: While Bromocresol Green is widely used, alternative indicators such as Methyl Red or Bromothymol Blue may also be employed under certain conditions or based on specific laboratory preferences. Each indicator has its pH range of color change, so the choice may vary depending on the exact nature of the sample and the titration conditions.
• Standardization: Regardless of the indicator chosen, it is imperative to perform a standardization of the titration procedure using a known nitrogen-containing standard. This practice ensures that the titration results are accurate and reliable.

In conclusion, Bromocresol Green serves as the preferred indicator for the titration step in the Kjeldahl method due to its effective and distinct color change at the relevant pH range. Ensuring the use of this indicator under optimal conditions will facilitate the accurate determination of nitrogen content in your samples.

Should you have further questions or require additional clarification on this matter, please do not hesitate to contact me.

Best regards.

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