What does standard additions mean?

Document ID

Document ID TE774

Published Date

Published Date 10/09/2019
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Question
What does standard additions mean?
Summary
Definition of standard additions
Answer
The standard additions method is a widely accepted technique for checking the accuracy of a test. While most Hach chemistries are compatible with a variety of sample types, there are a few analytical methods that only accurately work with a specific type of sample. Most Hach procedures list many types of samples compatible with the test. It is possible to determine whether a method is compatible with a specific sample by using standard additions. A standard addition (or standard spike) is a method of verifying the compatibility of an analysis method with a particular sample and determining if there are any substances in the sample that will interfere with the analysis method.

To perform a standard spike:
  1. Analyze an unspiked sample and record the sample concentration.
  2. Add a known amount of standard to a known volume of fresh sample.
  3. Repeat the test
  4. Check to see if the additional amount of standard was completely recovered.
Total recovery of the spiked standard supports that the sample is compatible with the test. Less than 90% or greater than 110% of recovered spiked concentration may indicate that a substance in the sample interfered with the sample analysis method. The sample may need to be pretreated before it can be analyzed, or an alternate testing method may need to be used.

Step-by-step instructions for the standard additions process are included as part of most Hach procedures under a section titled Accuracy Check, Standard Additions Method.

How to calculate recovery for Standard Additions

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