An Overview on Analytical Techniques in Chemistry
Diving into the intricate world of chemistry, an exploration of analytical techniques unfolds, offering a panoramic view of methodologies essential for unraveling the secrets held within chemical substances. Read An Overview on Analytical Techniques in chemistry laboratories for smooth analysis operations.
Author
Izaz Ul Islam
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What Is a Quality Control Chemist?
A quality control chemist (QC chemist) is a specific type of laboratory chemist, whose primary duties are to measure and test lab materials and products according to industry-specific standard procedures. Jobs are typically in the pharmaceutical or manufacturing fields. As a QC chemist, you assure adherence to all federal regulations and safety procedures. In addition to performing rigorous quality assurance of samples, some QC chemists are responsible for calibrating and performing maintenance on lab equipment. Relevant qualifications for this career include a bachelor’s degree in chemistry, experience in a chemistry lab setting, and skills like attention to detail and the ability to multitask.
Duties and Responsibilities:
There are the following duties that have to be performed by the Qc chemist officer.
· Organize raw materials
· Test products before, during, and after production
· Coordinate waste management
· Follow all company and governmental safety procedures
· Clean, maintain and store testing tools and equipment
· Create thorough reports on tests and your findings
· Evaluate testing protocols and suggest improvements.
Need to understand Importance of Analytical Chemistry
· In today’s era, the analytical chemist has a significant role, and to carry that role appropriately, they need to have the required skills and stick to an ethical code of conduct.
· Analytical research and development work in laboratories
· Drug formulation and development
· Chemical or forensic analysis
· Process and product development
· Product validation
· Quality control
· Toxicology
· Verify compliance with regulatory requirement
Work in marketing and law
· Teaching
· Food and Agriculture
· Oil and Petroleum
· Design instruments used in analytical analysis.
Important Questions you may ask during the Interview.
this section is a further extension of the topic, An Overview on Analytical Techniques in Chemistry.
Firstly, we have clarity in minds that why we selected analytical chemistry to study in this era of advanced sciences. Let go to sections that are important to understand chemistry.
1.U.V Visible:
Q. Basic Principle of U.V?
When matter absorbs ultraviolet radiation, the electrons present in it undergo excitation. This causes them to jump from a ground state (an energy state with a relatively small amount of energy associated with it) to an excited state (an energy state with a relatively large amount of energy associated with it). It is important to note that the difference in the energies of the ground state and the excited state of the electron is always equal to the amount of ultraviolet radiation or visible radiation absorbed by it.
Q Ranges of U.V and Visible?
200-400 U.V
400-800 Visible Below
200 vacuum region
Q. Calibration of U.V.?
The most commonly used solution for checking absorbance accuracy is potassium dichromate. Method tests absorbance at four wavelengths – 235, 257, 313 and 350 nm using between 57.0 and 63.0 mg of potassium dichromate in 0.005 M sulphuric acid diluted to 1000 mL. Since 2005 a second solution has been added to provide an additional test point at 430 nm. This uses the same amount of potassium dichromate but is made up to 100 mL (i.e. it is ten times more concentrated than the original solution). In both cases the A 1%/1 cm value is recorded and checked against the target range.
Wavelength accuracy is normally assessed by using either a sample containing a series of very sharp peaks such as a solution of holmium perchlorate or a holmium oxide and/or didymium doped glass filter or by measuring the emission from a lamp. If the instrument is equipped with a deuterium (D2) lamp as the UV source, this can be used. An external mercury (Hg) lamp can also be used. This is less convenient than using the previously mentioned methods but methodology exists (e.g. in the Ph. Eur. tests) for its use as an alternative to a glass or liquid standard. The advantage of emission lines is that they are inviolate (i.e. the emission wavelengths don’t change over time)
Q. On which principle U.V works?
It works on Lambets Beer Law
Q. Lamberts Beer Law?
As per the Beer-Lambert law, the greater the number of absorbing molecules (that have the ability to absorb light of a specific wavelength), the greater the extent of absorption of the radiation.
A=C ×L Q.
Transmittance and Absorbance?
Transmittance (T) is the fraction of incident light which is transmitted. In other words, it’s the amount of light that “successfully” passes through the substance and comes out the other side. Absorbance (A) is the flip-side of transmittance and states how much of the light the sample absorbed. It is also referred to as “optical density
Q. which Range of absorbance that follow lamberts Beer Law?
0—2 Absorbance
What kinds of detectors are used in UV-Visible spectroscopy?
A widely used detector in UV-Vis spectroscopy is the Photomultiplier tube. It consists of a photoemissive cathode (which is a cathode that releases electrons when it is hit by radiation photons), multiple dynodes (which is a device that emit multiple electrons for each striking electron), and an anode.
Light Sources
Hydrogen-Deuterium lamps are most widely used and suitable light source as they cover the whole UV region. Tungsten filament lamps are rich in red radiations used in visible Region.
2. FTIR:
Q. Basic Principle of FTIR.
FT-IR stands for Fourier Transform InfraRed, the preferred method of infrared spectroscopy. In infrared spectroscopy, IR radiation is passed through a sample. Some of the infrared radiation is absorbed by the sample and some of it is passed through (transmitted).A the result the molecules goes on vibrating of different types, as the wavelenth becomes longer the energy is not much enough to transist the radiations.
Q. What is Fourier transformer method?
The term Fourier-transform infrared spectroscopy originates from the fact that a Fourier transform (a mathematical process) is required to convert the raw data into the actual spectrum.
Q. Range of FTIR.
The commonly used region for infrared spectroscopy is 4000 ~ 400 cm-1. Near-infrared region (12800 ~ 4000 cm-1 ), mid-infrared region (4000 ~ 200 cm-1 ) and far-infrared region (50 ~ 1000 cm-1 )
Q. Solvents used in FTIR.
Commonly used solvents in IR solution cells are CCl4, CS2, and CHCl3; they are usually transparent in the important absorption region of the spectrum. Many organic compounds and polymers have poor solubility in IR solvents, such as CCl4, CS2
Q. Regions of FTIR.
The region between 400 cm-1 and 1500 cm-1 is known as the fingerprint region, so called because it’s difficult to assign all the absorption bands, and because of the unique patterns found there. Absorption bands in the 4000 to 1450 cm-1 region are usually due to stretching vibrations of diatomic units, and this is sometimes called the group frequency region.
3. HPLC:
Q. Basic Principle of HPLC.
The separation principle of HPLC is based on the distribution of the analyte (sample) between a mobile phase (eluent) and a stationary phase (packing material of the column). Depending on the chemical structure of the analyte, the molecules are retarded while passing the stationary phase.
Q. Types of Column used in HPLC.
Silica gel is the earliest chromatographic column packing used in liquid chromatography. It has a wide range of applications. However, it can only be used under the condition of pH 2.0-7.5.
C18 is the most commonly used non-polar reversed-phase column, and it has a wide range of applications. And the separation effect is good.
Cyano and Diol ion HPLC Columns.(Polar columns).
Q. Difference between C8 and C18 columns
C18 retain non polar compounds (Hydrophobic) while C8 has low hydrophobicity. As the carbon chains increases the polarity of columns will be reduced.
Q. normal and Reverse phase Chromatography and their Columns.
The main difference between normal phase and reverse phase chromatography is that normal phase chromatography has a very polar stationary phase and a non-polar mobile phase whereas reverse phase chromatography has a non-polar stationary phase and a polar mobile phase. Furthermore, the stationary phase of the normal phase chromatography is mainly pure silica, and the mobile phase is a non-aqueous solvent such as chloroform while the stationary phase of the reverse phase chromatography is a modified silica substrate with long hydrophobic long chains and the mobile phase is mainly water, methanol or acetonitrile.
Q. How HPLC gives quantitative and qualitative Analysis.
Peak area gives us quantitative and retention time determines qualitative
Retention time.
The retention time refers to the time which is required for a compound from the moment of injection until the moment of detection. Accordingly, it represents the time the analyte is in the mobile and stationary phase
Difference between HPLC & UHPLC.
The main difference is the size of used particles filled into the column. Particle sizes ≤ 2 µm are commonly used for UHPLC. Particles with a size of 3 µm up to 5 µm are usual for classical analytical HPLC
Q. What are hyphenated Techniques.
Combination of Chromatography and spectroscopy bring to hyphenated methods .e.g LCMS (HPLC-mass spectroscopy)
Components of HPLC.
The HPLC system mainly consists of an infusion pump, a sampler, a chromatographic column, a detector, and a data recording and processing device. Among them, the infusion pump, the chromatographic column, and the detector are key components. In addition, the gradient elution device, online degasser, auto sampler, pre-column or guard column, and column temperature controller can also be configured as required.
Types of Detectors in HPLC.
UV Visible detector
Refractive index detector
Evaporative light scattering detectors
Photodiode array Fluoresce Detector
Conductivity detectors
Q. Role of Equilibrium in separation?
Equilibration buffer is made to equilibrate the system (here it’s a column) with defined condition supposed to favor the first step in affinity chromatography which is to adsorb the molecule of interest onto the solid matrix.
Q. Types of Mobile phase?
Gradient: Polarity of Mobile phase is same during whole analysis
Isocratic: Polarity of Mobile phase is changes during analysis.
Things important for operation of HPLC.
· Degassing of mobile phase
· Proper dissolvation of sample.
· Column Washing
· Column saturation with Mobile phase before starting analysis.
· Fimilarization of nature of sample (to select column)
· Sample Filtration at micro levels.
· After analysis again washing of column.
Column washing and Care.
Start any wash procedure at the end of your day with the replacement of any buffer or modifier. In your case wash the column with 70% water; 15% methanol; 15% acetonitrile. Divert the column eluent to waste not to contaminate your detector(s). Wash the column slowly over to 100% methanol and wash for at least 15 minutes. Wash the column over to 100% acetonitrile and wash for at least 15 minutes. Depending on the type of column you are using you can store the column in 100% organic depending on the manufacturer’s recommendations. We store most of my C18 columns in 100% acetonitrile and the columns last for years.
4. Statistical Data Questions:
this section is an addition to the topic, An Overview on Analytical Techniques in Chemistry.
Accuracy:
Refers to how closely the measured value of a quantity corresponds to its “true” value.
Determinate errors:
These are mistakes, which are often referred to as “bias”. In theory, these could be eliminated by careful technique.
Error analysis:
Study of uncertainties in physical measurements.
Indeterminate errors:
These are errors caused by the need to make estimates in the last figure of a measurement, by noise present in instruments, etc. Such errors can be reduced, but never entirely eliminated.
Mean (m):
Defined mathematically as the sum of the values, divided by the number of measurements.
Median:
Is the central point in a data set. Half of all the values in a set will lie above the median, half will lie below the median. If the set contains an odd number of datum points, the median will be the central point of that set. If the set contains an even number of points, the median will be the average of the two central points. In populations where errors are evenly distributed about the mean, the mean and median will have the same value.
Precision:
Expresses the degree of reproducibility, or agreement between repeated measurements.
Range:
Is sometimes referred to as the spread and is simply the difference between the largest and the smallest values in a data set.
Random Error:
Error that varies from one measurement to another in an unpre- dictable manner in a set of measurements.
Sample:
A substance or portion of a substance about which analytical information is sought.
Sampling:
Operations involved in procuring a reasonable amount of material that is representative of the whole bulk specimen. This is usually the most challenging part of chemical analysis.
Sampling error:
Error due to sampling process(es).
Significant figures:
The minimum number of digits that one can use to represent a value without loss of accuracy. It is basically the number of digits that one is certain about.
Standard deviation (s):
This is one measure of how closely the individual results or measurements agree with each other. It is a statistically useful description of the scatter of the values determined in a series of runs.
Variance (s2):
This is simply the square of the standard deviation. It is another method of describing precision and is often referred to as the coefficient of variation.
5. Some General Questions:
this section is an addition to the topic, An Overview on Analytical Techniques in Chemistry.
Q. Explain What Is Buffer?
A buffer is an aqueous solution which has highly stable pH. It is a blend of a weak acid and its conjugate base or vice versa. On adding small amount of base or acid to buffer, its pH hardly change
Q. What Is Use Of Ion Pair Reagents?
The chemical substances that pair each other, to form complexes. These can use for stabilization of one of the molecule that is more active or to colorifying etc
Question 4. Explain What Is A Base Line?
Base line is nothing but the detectors response to the mobile phase
Q. What Is Use of Acetonitrile Compare to Methanol In Rp-hplc Method Development?
ACN is highly polar as compare to Methanol So provide Better resolution for many compound and it has property to form hydrogen bond so provide better selectivity.
Q. What Is Quality Control?
Quality control means to maintain the quality of product by calculating their content, different physical parameters, as per their specification IP/BP/USP/EP/JP.
Q. When We Get Moisture Content By Kf Higher Than By Lod, What Does This Indicate?
KF titration is the most accurate method in analyzing moisture content. But it is costlier and maintaince is too high. So in analysis of moisture content an alternative experiment is Loss on Drying (LOD), which gives approximate moisture value present in the given substance.
Explain The Term Aliquot And Diluent?
Aliquot: It is a measured sub-volume of original sample Diluent: Material with which sample is diluted.
What is difference between QC and QA
Although QA and QC are closely related concepts, and are both aspects of quality management, they are fundamentally different in their focus:
· QC is used to verify the quality of the output;
· QA is the process of managing for quality.
Q. What is LOD/LOQ
LOD: Minimum amount of analyte that can be detected.
LOQ: Minimum amount of analyte that can be quantified.
Difference between Distilled and Deionized water?
Distilled water is free of inorganic materials, suspended impurities, and most organic contaminants. To make or buy distilled water is expensive. While there may be school laboratory applications where distilled water is required, in many applications, deionized (aka demineralized) water will do just as well. Deionized water, like distilled water, is free of inorganic materials and most suspended contaminants. If you need organic-free water, buy a still or buy distilled water.
Q. Hardness of water:
The greater amount of Ca and Mg determines hardness of water.
What is Good Laboratory Practice (GLP)
Good Laboratory Practice contains a set of principles that provides a framework within which laboratory studies (Activities) are planned, performed, monitored, recorded, reported and archived. GLP help assure regulatory authorities that the data submitted are a true reflection of the results obtained during the study and can therefore be confidence upon when marking risk/safety assessment. This is An Overview on Analytical Techniques in Chemistry.
What is Working & Reference Standard?
A reference standard is the traceable, raw material standard (usually in crystallized form) that we dissolve and volumetrically dilute to make our working standard. The working standard is what we use to “do our work.” and this information makes it traceable and is recorded in the preparation notebook.
A reference standard is prepared for use as the standard in an assay, identification, or purity test and should have a quality appropriate for its use.
Q. What is Assay test?
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a target entity (the analyte).
2.6 .Pharmaceutical Qc Questions:
this section is a further extension for the topic, An Overview on Analytical Techniques in Chemistry.
Disintegration Test:
It is the time required for the Tablet / Capsule to break into particles
Friability Test:
Friability is defined as the percentage of weight loss of powder from the surface of the tablets due to mechanical action.
Types of Tablets:
Coated, Sugar coated, Film coated, Enteric coated, capsules, Chewable tablets
Dissolution test:
Dissolution tests are performed to establish drug (Active Pharmaceutical Ingredient) release characteristics of solid oral products, such as tablets and capsules. The rationale for conducting these tests is that for a product to be therapeutically effective, the drug must be released from the product and should generally be dissolved in the fluid of the gastrointestinal (GI) tract. Q’ is the amount of dissolved active ingredient specified in the monograph which is required to be released in the stated time. This is An Overview on Analytical Techniques in Chemistry.
Which tablets are used in Calibration of dissolution Apparatus?
Non disintegrating (Salicylic Acid) and disintegrating (Prednisone) tablets are used in the calibration of dissolution test apparatus.
What is Out of Specification?
Out of Specification (OOS) means the test result that falls outside the specifications or acceptance criteria which has been specified in the official monographs or the Blend
Inside Qc department:
In process, Raw material, Packing material, Stability and finished product specification.
What is Out of Trend?
Out of Trend (OOT) means the test result that is within the specification limit or acceptance criteria as mentioned in the Blend, in process, Raw material, Packing material, Stability and finished product specification but outside the trend of previously tested batches.
Difference between Humidity and Relative Humidity?
Humidity – Measure of amount of water vapor present in the atmosphere.
Relative humidity– Water vapors amount exists in air expressed as a percentage of the amount needed for saturation at the same temperature
Tablets Test:
Dt test, Friability test, Dissolution test, Weight variation, Physical Apperance, Assay test
All test are performed according United state Pharrmacopeia,British Pharmacopeia and all complies authorties.
Injectables Tests:
Bacterial growth tests, Ph test, Conductivity test, Assay test.
Suspensions Tests:
Color , Odor, Ph Viscosity, Particle size, Redespersbility
7. Lab Accreditations:
this section is an extension of the original topic, An Overview on Analytical Techniques in Chemistry
Pakistan National Accreditation accredited first laboratory in 2004. SO/IEC 17025 is a company level accreditation based on a standard published by the International Organization for Standardization (ISO) titled “General requirements for the competence of testing and calibration laboratories”.17025 is advanced level of 17025.It has 15 Management requirements and 10 Technical requirements.
Also read: Difference Between Research Paper & Review Paper
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