Flow Injection Analysis: Caffeine Basics

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Questions and Answers

Which chemical group does caffeine belong to?

Alkaloid

Caffeine is the most widely used...What type of substance is it?

Psychoactive stimulant

What is the functional group of caffeine?

alkene, amide, and amine

What is the chemical formula of caffeine?

C8H10N4O2 Signup and view all the answers

What is the molecular mass of caffeine?

194.19 g/mol Signup and view all the answers

What does the peristaltic pump do?

Create a special flow that raises the small chambers in the carrier liquid Signup and view all the answers

What happens in the detector (in this case, a spectrometer)?

The detector measures the light that is not absorbed by the sample, and the amount that was absorbed is calculated from this. Signup and view all the answers

What is a mixing coil?

A thin tube in which the carrier fluid and the samples are transported to the measurement Signup and view all the answers

What is the purpose of the light source in a spectrophotometer?

A spectrophotometer contains a light source to emit light passing through a given solution. Signup and view all the answers

How is the sample loaded?

It happens automatically via an autosampler that can eject a precise amount of a sample and inject it into the carrier fluid. Signup and view all the answers

What is the purpose of optical fiber cable?

It transmits light from the light source and into the flow cell, where the sample is screened. Signup and view all the answers

There is no disposal waste after taking measurements from the FIA system. How much waste is there?

Small quantities of waste Signup and view all the answers

What is the purpose of the carrier liquid in the FIA?

It transports the samples to the detector for analysis. Signup and view all the answers

What is the function of the peristaltic pump?

To create a discontinuous flow and mix the sample with the carrier. Signup and view all the answers

After being mixed with the carrier, the sample travels through the...before being detected by the spectrophotometer.

Mixing coil Signup and view all the answers

How long does it take a sample with a flow rate of 0.5 mL/min to move through a mixing coil of 50 cm with an internal diameter of 0.8 mm to the detector?

30 seconds Signup and view all the answers

What should we do first, before we start measuring the samples?

Start the pump and wait until the flow is constant Signup and view all the answers

Which of the following is not an advantage of FIA?

It can detect the structure of the molecule Signup and view all the answers

What is the caffeine concentration in a cup (1 cup=237 mL) of brewed coffee containing 80 milligrams of caffeine?

1.738 mM Signup and view all the answers

How many grams of caffeine should we prepare in a 10 mL standard of 3 mM?

0.00583 grams Signup and view all the answers

I have prepared a caffeine stock solution of 0.075M. What volume should we mix with distilled water in order to reach a standard solution of 0.0015M and a final volume of 10 mL?

0.2 mL Signup and view all the answers

What does the x-axis show?

The time that it takes from the sample injection until detection. Signup and view all the answers

What does the Y-axis show?

The amount of light absorbed by the sample. Signup and view all the answers

How can we measure the actual sample concentration?

By comparing the sample's AU to the standard's AU. Signup and view all the answers

What should we do before measuring a solid sample, such as chocolate chips?

Grind the sample and make it soluble. Signup and view all the answers

How do we ensure that our unknown sample lies within the standard range?

We create 2-3 dilutions of our sample. Signup and view all the answers

Some of the samples do not have an AU value, and instead N/A is written. What does this mean?

The absorbance value is outside the detectable range. Signup and view all the answers

Using the standard curve, what is the gradient (m)?

466 Signup and view all the answers

What is the caffeine concentration in the undiluted dark chocolate sample?

0.00133M Signup and view all the answers

What is the approximate caffeine concentration in the syrup sample?

All possible answers might be correct Signup and view all the answers

Study Notes

Caffeine Characteristics

Caffeine is classified as an alkaloid, indicating a nitrogenous organic compound.
It functions as a psychoactive stimulant, affecting the central nervous system and altering consciousness, behavior, and mood.
The chemical formula of caffeine is C8H10N4O2.
Caffeine has a molecular mass of 194.19 g/mol.
Functional groups present in caffeine include alkene, amide, and amine.

Flow Injection Analysis (FIA) System

A peristaltic pump generates a special flow, facilitating the movement of samples through liquid.
The detector (such as a spectrometer) measures both the light absorbed and the light that passes through the sample to determine concentration.
A mixing coil is a thin tube for transporting the carrier fluid and samples to measurement devices.
The light source in a spectrophotometer emits light that passes through the solution for analysis.
Samples are automatically loaded via an autosampler, ensuring precise amounts are injected into the carrier fluid.
Optical fiber cables transmit light from the source to the flow cell for sample screening.
The FIA system produces only small quantities of waste after analysis.

Functions and Operations

The carrier liquid is essential for transporting samples to the detector for analysis.
The peristaltic pump creates a discontinuous flow to mix the sample with the carrier liquid.
Samples, after mixing with the carrier liquid, flow through the mixing coil before detection occurs.
To ensure a consistent measurement, the pump must be started and allowed to stabilize before sampling.

Calculations and Concentration

A brewed coffee cup (237 mL) containing 80 mg caffeine has a concentration of 1.738 mM.
Preparing a 10 mL standard solution at 3 mM requires 0.00583 grams of caffeine.
To create a 0.0015M standard solution from a caffeine stock of 0.075M, mix 0.2 mL with distilled water.
The concentration in undiluted dark chocolate is approximately 0.00133M.
The gradient (m) from the standard curve for absorbance readings is 466.

Measurement Insights

The x-axis in absorption spectrometry denotes the time from sample injection to detection, while the y-axis reflects the amount of light absorbed by the sample.
Actual sample concentration is determined by comparing the sample's absorbance units (AU) with a standard's AU.
Solid samples should be ground and dissolved prior to measurement to ensure accurate readings.
Duplicate or triplicate dilutions help ensure unknown samples fall within the detectable range.
An N/A value indicates that the sample's absorbance is outside the detection capability of the analysis system.

Sample Limitations

In some syrup samples, caffeine concentration may be undetectable due to preparation issues, absence, or it might be present beyond detection limits.

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Description

This quiz focuses on essential concepts related to caffeine and its chemical properties. Explore various chemical groups, functional characteristics, and its classification as a psychoactive stimulant. Test your knowledge about caffeine's role in chemistry and its effects on the central nervous system.