I have a 2000ppm benzoic acid solution.I want to prepare a 20ppm benzoic acid solution.Is it better to
1) do serial dilutions i.e. from 2000 to 200 to 20ppm
or
2) prepare 20ppm standard fresh when required( take 10ul of 2000ppm stock and top up to 1ml in a LC vial with 990ul 70% ethanol)
You want to dilute it 100 times, which means one part concentrated, 99 part dilutant.
I would do fresh, I always found the chance of contimination doubled with each dilution. Maybe I never had clean bottles.
I will see if I can get other views on this.
I have had the opposite experience from Bob Pursley. My problem has been that I never trusted the 10 ul pipets. Too large a relative error in 10 ul. Therefore, I always went the serial dilute route.
To prepare a 20ppm benzoic acid solution, you have two options: serial dilutions or preparing a fresh standard when required. Both methods can give you the desired concentration, but each has its advantages and considerations.
1) Serial dilutions: This method involves diluting a high concentration solution with a known concentration incrementally to obtain the desired concentration. In your case, you would need to perform multiple dilutions from 2000ppm to 200ppm and then down to 20ppm. Here's how you could do it:
- Take a known volume (let's say 1mL) of the 2000ppm solution and dilute it with a suitable solvent (such as distilled water or ethanol) to obtain a 200ppm solution.
- Then, take a known volume (e.g., 1mL) of the 200ppm solution and dilute it again to yield a 20ppm solution.
Advantages:
- Once you have prepared the diluted solutions, they can be stored for future use.
- You can use the diluted solutions for multiple analyses without having to prepare a fresh standard each time.
Considerations:
- Accuracy and precision are critical in serial dilutions, as any errors in pipetting or measurement can accumulate and affect the final concentration.
- Chemical stability of the solution may be a concern if stored for a long time, as some compounds may degrade over time.
2) Fresh standard preparation: This method involves preparing a fresh solution of the desired concentration each time it is needed. In your case, you would take 10μL of the 2000ppm stock solution and dilute it with 990μL of 70% ethanol in an LC vial to obtain a 20ppm solution.
Advantages:
- Eliminates any potential errors or concerns associated with serial dilutions.
- Ensures fresh and accurate standard solutions for each analysis.
Considerations:
- This method requires preparation each time you need a standard solution, which can be time-consuming if multiple analyses are required.
- It may require more stock solution if you need to perform several analyses.
Ultimately, the choice depends on the specific needs of your analysis. If you require a high degree of accuracy and precision, and you are performing multiple analyses, serial dilutions may be more suitable. Conversely, if you need to minimize time and maximize accuracy for each analysis, preparing fresh standards may be the better option.