LC with UV-detection (λ≈220 nm) is routinely used to separate herbicides such as atrazine and si

LC with UV-detection (λ≈220 nm) is routinely used to...

LC with UV-detection $(\lambda \approx 220 \mathrm{nm})$ is routinely used to separate herbicides such as atrazine and simazine: The presence of herbicides in drinking water is controlled by legislation, and the WHO recommended limit for each of atrazine and simazine is $0.002 \mathrm{mg} \mathrm{dm}^{-3} .$ The following questions relate to the LC-MS analysis of drinking water for atrazine and simazine. (a) What is meant by "UV-detection"? Suggest the origin of the absorption at $220 \mathrm{nm}$ (b) Internal standards of fully deuterated atrazine and simazine are used. Explain why they are added to all samples during both calibration and analyte runs. (c) How would you calibrate the LC instrument (bearing in mind the WHO recommended limits for atrazine and simazine) and how would you determine the concentrations of the herbicides in a sample of drinking water? (d) Why does the analyst record the mass spectrum in addition to LC data for each analyte?

LC with UV-detection $(\lambda \approx 220 \mathrm{nm})$ is routinely used to separate herbicides such as atrazine and simazine:
The presence of herbicides in drinking water is controlled by legislation, and the WHO recommended limit for each of atrazine and simazine is $0.002 \mathrm{mg} \mathrm{dm}^{-3} .$ The following questions relate to the LC-MS analysis of drinking water for atrazine and simazine.
(a) What is meant by "UV-detection"? Suggest the origin of the absorption at $220 \mathrm{nm}$
(b) Internal standards of fully deuterated atrazine and simazine are used. Explain why they are added to all samples during both calibration and analyte runs.
(c) How would you calibrate the LC instrument (bearing in mind the WHO recommended limits for atrazine and simazine) and how would you determine the concentrations of the herbicides in a sample of drinking water?
(d) Why does the analyst record the mass spectrum in addition to LC data for each analyte?

Key Concepts

Mass Spectrometry for Analyte Confirmation

Mass spectrometry, when coupled with liquid chromatography, provides additional structural and mass information that facilitates the confirmation of analyte identity. Recording the mass spectrum alongside the LC data helps to distinguish the target compounds from co-eluting or interfering substances and supports the identification of compounds based on their mass-to-charge ratios. This dual-detection strategy enhances both the selectivity and reliability of the analysis, particularly in complex samples such as drinking water.

Calibration in LC-MS Analysis

Calibration in LC-MS involves preparing a series of standard solutions with known concentrations of the target analytes, ideally spanning the concentration range relevant to regulatory limits. A calibration curve is then constructed by plotting the detector response (often corrected using the internal standard) against the known concentrations. This curve is used to interpolate the concentration of analytes in unknown samples, ensuring that the quantification is accurate even at low levels mandated by legislation.

UV Detection

UV detection in liquid chromatography refers to the use of a UV spectrophotometer to monitor the eluent from the LC column based on its absorbance of UV light. Molecules possessing conjugated double bonds or aromatic rings can absorb UV radiation, typically resulting in electronic transitions, and the detection wavelength is chosen based on the specific absorption characteristics of the analytes. In many cases, 220 nm is selected because it corresponds to a strong absorption band for many organic compounds with such structural features.

Internal Standards

Internal standards are compounds, often isotopically labeled analogues, that are added in a constant amount to all samples, including calibration standards and unknowns. These compounds behave similarly to the analytes during sample preparation and analysis but can be distinguished by the detector, such as in mass spectrometry. Their use helps to account for variability in sample injection, matrix effects, and instrumental drift, thereby improving the accuracy and precision of the quantitative analysis.

Transcript

00:08 In this question, we are told that lc with uv detection, so we have an lc with uv detection, and the wavelength that is approximately 2, 20 nanometer, was used to separate herbicide, such as atrazine, and the presence of herbicide in vector water is controlled by legislation.

00:47 And the world health organization recommend with each atrazine and simazine to be 0 .002 become a computer simulator.

00:58 So the following question relates to the lcms, which is the group chromatography, mass spectrometry analysis of drinking water of atrazine and simazin.

01:09 So the first question is, what is meant by uv detection? so what do we mean by, uv detection.

01:22 So in order to answer this question, first we'll need to talk about the mini -hop for uv.

01:28 Uv is control violence, which is a section in the electromagnetic spectrum where you have other ones like the high heart and the visible and so on and support.

01:48 For uv, it is usually the wave lines that is used here with 220 nanometer.

02:01 So it's like ultraviolet light and it's high energy.

02:05 I have done the visible light.

02:07 The visible light is just a red to the violet light, which is the one that is visible to the human heart.

02:13 But the ultraviolet light is not actually visible to human light.

02:18 Anyways, so we have to suggest what is meant by uv detection.

02:24 So we define what uv is, short -valence, wavelength distance and 400 nanometer.

02:31 So the way that works is that at these wavelengths, that's 220 nanometer, there will be an absorption.

02:39 So if this is the wavelength, which increases in this direction, and for example, maybe this can be the absorbance.

02:51 So when you pass a sample through the lc, then you're looking at a wavelength, at 220 nanometer you will see an absorption and that absorption is characteristic of the compound of interest which in this case is atrazine a similar sensor.

03:10 This is around 220 nanometer absorption of those compounds.

03:22 So that is how you can detect a compound by uv detection through the lcms and whenever you see an absorption at that specific footprint that is characteristic of that compound.

03:35 So that answers that question.

03:38 And the next question is, internal standards of fully caterated atrazine and c -maxen are used.

03:49 So here we talk about internal standard.

04:00 So the question wants us to explain why they are added to all samples during both calibration and analytron.

04:09 So internet standard, i use.

04:12 For quantification.

04:19 They are based for quantification...

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