What Is Auto Zero in UV-VIS Spectrophotometer? – Let’s Find Out

A UV-Vis spectrophotometer’s auto-zero capability enables the instrument’s baseline drift or noise to be automatically corrected.  The current wavelength will automatically be set to 100% transmittance (zero absorption) when you press the ‘Auto Zero’ key.

The spectrophotometer detects the absorbance of the blank solution when the auto-zero mode is turned on, and it automatically resets the baseline to zero. In order to account for baseline noise or drift, it subtracts the observed absorbance of the blank from subsequent sample measurements.

Functions of Auto Zero Mode in UV-VIS Spectrophotometer

The baseline in UV-Vis spectrophotometer is the absorbance value of the solvent or blank solution when no sample is present. The baseline should ideally be a fixed absorbance value of zero. The baseline can, however, drift or diverge from zero as a result of elements like electronic noise, temperature variations, or minor contaminants in the solvent.

Fig. 1: Baseline Drift in UV-Vis Spectrophotometer

Eliminating baseline drift is crucial to achieving reliable readings, particularly for samples with low absorbance values. The auto-zero feature is useful in this situation. The spectrophotometer ensures that the true absorbance of the sample is measured, regardless of any changes in the baseline, through automatic zeroing. 

This feature improves UV-Vis spectrophotometric measurements’ precision and dependability, especially for samples with low absorbance values or where long-term stability is essential. An outline of the typical measurement procedure using auto zero is provided below.

Blank Measurement

The spectrophotometer measures the absorbance of the blank solution that has been placed in the cuvette. Any baseline drift or noise that the instrument may have is measured by this measurement. Assume that the spectrophotometer reads an absorbance value of 0.02 AU (arbitrary units) when measuring the blank solution.

Baseline Correction

A reference value is employed, which is the measured absorbance of the blank. By deducting the recorded blank absorbance from successive sample measurements, the spectrophotometer automatically resets the baseline absorbance to zero. For example, to adjust the baseline, the measured absorbance of the blank solution, 0.02 AU, is utilized as a reference.

Sample Measurement 

The spectrophotometer measures the sample solution’s absorbance once the baseline has been adjusted. Subtracting the corrected baseline absorbance yields the absorbance value that has been corrected for the baseline. Let’s say you measure a sample solution’s absorbance and get a result of 0.10 AU.

Result Analysis

The calculated baseline-corrected absorbance value is used to make additional calculations, such as calculating the concentration or examining the spectral properties of the sample. You deduct the corrected baseline absorbance from the sample measurement to get the absorbance value that has been adjusted for the baseline. For example,

Sample Absorbance – Baseline Absorbance = Baseline-Corrected Absorbance

Absorbance corrected for the baseline = 0.10 AU – 0.02 AU

Absorbance corrected for baseline = 0.08 AU

The derived baseline-corrected absorbance value of 0.08 AU accurately captures the sample’s actual absorbance, regardless of baseline alterations. The spectrophotometer performs this calculation automatically when the auto zero function is turned on. 

It makes sure that any differences in the baseline are taken into account when adjusting the recorded absorbance values, leading to more precise and trustworthy data analysis, such as concentration determination or spectrum analysis.

Benefits of Auto Zero in UV-VIS Spectrophotometer

The auto-zero feature has a number of benefits. Some of them are given below:

Enhanced Accuracy

The auto-zero function improves the accuracy of absorbance measurements by adjusting for baseline drift and noise. It makes sure that sample features, rather than instrument changes, are predominantly reflected in the recorded absorbance values.

Superior Sensitivity

Particularly helpful for samples with low absorbance values is the auto-zero function. It enables the accurate identification of minute fluctuations in sample concentration or spectral characteristics by allowing for the assessment of minor changes in absorbance.

Long-lasting Stability

The auto-zero function contributes to the stability of the instrument’s measurements over long periods of time by automatically adjusting the baseline at predetermined intervals.

Frequently Asked Questions and Answers – FAQs

If I Don’t Have Problems With Baseline Drift, Can I Turn off the Auto Zero Feature?

As a precaution, it is typically advised to keep the auto zero function turned on. The auto zero capability can, however, be turned off if preferred if baseline stability is verified and validated through the required controls and inspections.

How Frequently Should I Use the Auto Zero Feature?

Depending on the instrument in question and the circumstances of the experiment, auto-zeroing occurs frequently. It is advised to use the auto zero feature on a regular basis or anytime baseline drift is noticed, usually at the beginning of a measurement session or following significant changes in the environment.

Conclusion

In UV-Vis spectrophotometers, the auto zero function is a useful feature that automatically corrects for baseline drift or noise. It makes sure that measurements of sample absorbance are precise and trustworthy by measuring the absorbance of the blank solution and setting the baseline to zero.