Analytical Chemistry - Science method

Dears,

I'm using the UV/vis method to determine water-soluble chrome in cement as follows:

I take particulate mass from dichromate to make a stock solution then take various volumes of aliquots into a 50 ml volumetric flask to set up a calibration curve.

for measuring the sample, I take a 25 g sample and 25 ml of water then filter and take 5 ml of filtrate into a 50 ml volumetric flask and dilute to mark with water after adding a color indicator.

my inquiry why don't I consider 50 ml dilution of aliquoted sample in the calculation equation ? and if I deviate from the method and make a dilution of the aliquoted sample 100 ml instead of 50 ml what does the formal calculation equation become?

#analytical Chemistry

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Thierry

After performing boehm titration using HCl,NaOH, Na₂CO₃, and NaHCO_3.  I want to know the formula to calculate functional groups.

I am measuring primary aromatic amines by UV-VIS and using the NEDA solution as my coupling reagent. The method says that the reagent needs to be made fresh every day. However, the solution is sold commercially from 0.1-1.0% with a shelf life of 6-12 months. Why does it have to be made fresh? What is its stability? Is it a temperature or UV dependent reaction? Can storing in a brown(amber) bottle and/or refrigerating allow for longer use?

Dear colleagues,

We have recently optimized a TDS-GC-MS method for VOCs (SVOCs) analysis. (Gerstel + Agilent).

A high-temperature column with mid-polarity is chosen for a better resolution (similar to DB-624ms but with a higher operating temperature of 300/320 °C).

Although the desired separation is achieved with a programmed-temperature method (final temperature: 290 °C), some analytes with low boiling points, such as dichloromethane, benzene, and heptane, show unacceptable intensity variation. (The RSD of three replicas can be as high as 30%). On the other hand, compounds with higher boiling points (such as naphthalene and pentadecane) are more stable. (RSD < 5%)

We further lower the final temperature of the method (from 280 °C to 260 °C), and the repeatability of benzene and heptane is much better (RSD < 5%), while the dichloromethane is still fluctuating (RSD ~ 15%).

Any explanation for this phenomenon?

p.s. the column pressure can be very high under high-temperature

In 2009, while investigating whether injections of methylcobalamin would help my chronic health condition, I chanced upon an intriguing happenstance. The contents of four vials (from a batch of twelve vials) were remarkably effective. All up, over a two-year period I injected methylcobalamin from a total of 41 vials (from four different batches). Injections from 37 of the vials made no impact whatsoever on my condition. Injections from the four effective vials were not consecutive so this wasn't a situation where an initial good response waned.

From the batch of twelve vials that contained four effective vials, the first two effective vials were discarded after use. I saved the remaining ten used vials.

In early 2012 I had the dregs from the ten vials analysed (HPLC at 361 nm). Unfortunately I could not distinguish the two effective vials from the other eight vials so the best I could achieve was to discover if there was anything different about two of the ten vials.

A methylcobalamin injection in light-protected glass ampoule from a different manufacturer was used as the standard (i.e. Methycobal® made by Eisai Co Japan).

Along with the dregs from ten used vials, content from an unused but expired vial (which had been stored correctly) and content from an unused but current vial (sent directly to the analytic lab from the manufacturer's premises) were analysed.

HPLC indicated the standard (i.e. Methycobal®) was pure. It contained two major peaks, the main being MeCbl (eluted at ~ 19 mins) with a smaller OHCbl peak (eluted at ~ 13 mins). Identity of these peaks was subsequently confirmed by MS.

HPLC of the remaining 12 samples (10 x dregs from used vials + 1 x expired vial + 1 x current vial) indicated all were similar to each other. All 12 samples contained four major peaks. Two of these major peaks corresponded to the two peaks in the standard (i.e. MeCbl + OHCbl). Relative ratios of these peaks was as expected – i.e. more MeCbl had degraded to OHCbl according to age of product.

All vials contained significantly more MeCbl than OHCbl (gauged visually from height/width of peaks and subsequently confirmed by calculation of area under peak).

The lab is a reputable commercial lab with up-to-date equipment.

The results look 'pristine'.

All major peaks are symmetrical, narrow, distinct, well separated, no tailing, twin peaks etc.

The lab ran blanks before and between samples.

The order of run was –

10 x dregs* > 1 x expired vial > 1 x standard (Methycobal®) > 1 x current vial

* The first 4 x dregs were rerun the following morning (approx 20 hrs later) because operator was not happy with initial results (I think there was rt drift)

Additional listed ingredients do not account for the unidentified peaks.

Additional listed ingredients –

• Methycobal® – D-mannitol 50 mg (per 500μg MeCbl in 1mL ampoule)

• The vials – Sodium Chloride 18 mg (per 10,000 μg MeCbl in 2mL vial)

Neither product contains preservative.

Concentration of the samples for analysis made from the dregs varied due to variable volume of dregs in each vial.

Looking at the HPLC chromatogram –

Visually it is obvious that two of the ten vials with dregs contain significantly more of one of the two unidentified major peaks (eluted at ~ 15 mins). Relative to the height of the MeCbl peak this peak is ¼ to ⅓ MeCbl height in 8 x dregs. In 2 x dregs it is around ½ the height (i.e. there is around twice as much of this substance in 2 x dregs than in the other 8 x dregs).

I used the height (mAU) of the MeCbl peak to plot a standardised graph of the height of the peaks in Excel. That is, I multiplied the mAU for the MeCbl peak of each sample by a factor^ so that MeCbl peaks from each sample were equal – i.e.they appear as a single dot on the Excel graph. (In the chromatogram the mAU of the MeCbl peak for the standard + expired and current vials was similar but the mAU for the dregs varied due to limited volume available for analysis.)

^ For each sample, mAU of each major peak was raised by the same factor (i.e. factor needed to equalise MeCbl).

When plotted in Excel the results look orderly. The unidentified peak at 15 mins is more or less the same height as the OHCbl peak for all samples except for 2 x dregs. The unidentified peak at ~ 12 mins is a little lower than the OHCbl peak in all samples. (These two peaks are missing from the standard.)

The OHCbl peak is lowest in the current vial and in the standard – I'll call this the baseline. OHCbl peak is approx 70% higher than baseline in expired vial and in 6 x dregs (in 4 x dregs OHCbl is ~ 55% higher than baseline).

The unidentified peak at 12 mins is lowest in the current vial (baseline). It is around 70% higher in the expired vial, and higher still in the 10 x dregs (varies from 130% to 250% higher than baseline, evenly distributed through this range).

The unidentified peak at 15 mins is lowest (baseline) in current and expired vials (around 20% higher in expired than in current vial). In 8 x dregs the height of this peak varies from 36% to 85% higher than baseline (evenly distributed through this range). In 2 x dregs the height of this peak is 200% to 220% higher than baseline.

The baseline for each peak:

~12 mins 175 mAU

~13 mins (OHCbl) 375 mAU

~15 mins 357 mAU

~19 mins (MeCbl) 2270 mAU

At the time of HPLC analysis the attitude from analytical lab and manufacturer of vials was that it was virtually impossible for there to be any difference between vials within a batch. The lab's report – on the HPLC chromatogram – advised all vials were similar and did not comment on the disparity between height of peak at 15 mins in 2 x dregs. The lab attributed the extra two major peaks in the vials to an unlisted ingredient (when questioned the manufacturer resorted to legalese, but it is unlikely there are any unlisted ingredients in the vials).

The lab considers the method it used its IP and will not disclose. However, it used a phosphate buffer. After HPLC there was no residue left to analyse in the 10 x dregs. The lab suggested it could develop a different method, suitable for LC-MS, and run a sample from the expired or current vial. It offered to provide raw data on 20 peaks but I would not know which, if any, of the 20 peaks corresponded to the two unidentified major peaks found in previous HPLC. I couldn't see the point of this exercise.

I sent all samples to another lab (at a major university). The lab advised there was no residue for analysis in the 10 x dregs. It analysed a sample from the expired vial and from a new (unopened) ampoule of Methycobal®. The previous lab would not disclose its method so this lab used the method outlined in Japanese Pharmacopoeia, although it used 361 nm rather than 266 nm. This lab could not find the additional two major peaks (using C8 reverse phase ODS column with phosphate/methanol buffer it found only MeCbl and OHCbl in both samples, which it identified using MS). In further attempt to find the additional two major peaks the lab used a C18 column with water and acetonitrile under acidic conditions but chromatograms from the two samples again looked identical (with two major peaks). The lab attempted to identify these two fractions using static nanospray MS but results were inconclusive – "It is worth noting the fractions collected did not contain the pink colour common to all cobalamins. . . . The ion counts from all the fractions were quite low which was surprising given that the fractions should have been very concentrated."

The analytical chemist later elaborated on this aspect of her report –

"I cannot say definitively that these peaks from the C18 column are not cobalamin. It is possible that only a small amount of cobalamin eluted and the majority remained on the column. However, it is also possible that it was not cobalamin but something else which did not ionise using ESI and therefore could not be identified. The evidence is not conclusive one way or the other."

The samples were returned to the first lab for repeat analysis under identical conditions (I requested this include using the same HPLC analyser and operator).

The lab was certain its previous HPLC did not find ghost peaks and was sure it would find the peaks again, so it considered my request for identical conditions unnecessary.

HPLC was run using same method but different analyser and operator. The results were more or less nonsensical. The lab advised it was the fault of the samples (it claimed the university lab had most likely mishandled the vials/ampoule). The chemist advised that he believed material in vials and ampoule had fully degraded to OHCbl prior to analysis. I thought the results indicated the samples had degraded rapidly during HPLC.

Eventually the lab agreed to run HPLC again, but again declined to use original analyser and operator.

This time it checked degradation of samples over time (and included an MECbl standard purchased from Sigma-Aldrich).

Results indicated that material in the vials and ampoule had not degraded (plenty of MeCbl was present). However, results also indicated that samples degraded rapidly (to OHCbl) when in the buffered diluent that was used in original HPLC analysis – samples completely degraded to OHCbl after 12 hours in autosampler. And yet, during the original HPLC, four of the samples sat in the autosampler for approx 20 hours before being reanalysed at 9 am the following morning, and those samples showed no sign of degradation during storage (the 2 x outlier dregs were among these four samples). When asked to explain this discrepancy the lab advised that the original autosampler was refrigerated whereas the one used for the time study was not.

The lab now offers to inject a single sample (from the expired vial) using the original analyser and the original operator. This almost meets my request to rerun the analysis under identical conditions, except for the method of injection (autosampler vs manual injection). In reading through many troubleshooting guides available online I get the impression that manual injection (if done well, i.e. completely fill the loop) is more likely to produce reliable result than injection from an autosampler. Also, will temperature of injection vary (i.e. will manual injection be at same temperature as one from refrigerated autosampler)? How important is temperature?

Is it unusual for ghost peaks to produce such orderly results?

I came across the bi-amperometric technique in analytic chemistry, but I don't understand why the analysis is possible only if the sample contains reversible redox couples. Before of that I'd like to understand when a redox reaction could be defined as reversible and when it cannot.

Thanks in advance.

Is there a technological niche in pharmaceutical research that makes NQR or NMR the only measurement methods practically applicable?

Hello,

I actually have a salt of potassium formate, but the issue is that there are many impurities in the salt. I wanted to know which analytical technique is appropriate to quantify the composition of the salt as well as identify all the impurities present in the salt.

I am thinking of HPLC and GC-MS. Which of these is better and how to go about it? Lastly, are there any better methods than the ones I have listed? There is a lab with most of the equipment, but I just want to make sure I go with the most suitable one.

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Abstract:

Over the past few decades, instrumental analysis has come a long way in terms of sensitivity, efficiency, automation, and the use of sophisticated software for instrument control and data acquisition and processing. However, the full potential of such sophistication can only be realized with the user’s understanding of the fundamentals of method optimization, statistical concepts, calibration strategies and data processing, to tailor them to the specific analytical needs without blindly accepting what the instrument can provide. The objective of this course is to provide the necessary knowledge to strategically exploit the full potential of such capabilities and commonly available spreadsheet software. Topics to be covered include Analytical Statistics, Propagation of Errors, Signal Noise, Uncertainty and Dynamic Range, Linear and Non-linear Calibration, Weighted versus Un-Weighted Regression, Optimum Selection of Calibration Range and Standard Intervals, Gravimetric versus Volumetric Standards and their Preparation, Matrix effects, Signal Drift, Standard Addition, Internal Standards, Drift Correction, Matrix Matching, Selection from multiple responses, Use and Misuse of Dynamic Range, Evaluation and Visualization of Calibrations and Data from Large Data Sets of Multiple Analytes using EXCEL, etc. Although the demonstration data sets will be primarily selected from ICPES/MS and Chromatographic measurements, the concepts discussed will be applicable to any analytical technique, and scientific measurements in general.

Learning Objectives:

After this course, you will be familiar with:

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Access to a personal laptop for the participants during the course would be helpful, although internet access during the course is not necessary. However, some sample- and work-out spreadsheets, and course material need to be distributed (emailed) to the participants day before the course.

Target Audience: Analytical Technicians, Chemists, Scientists, Laboratory Managers, Students

Is there a technological niche in pharmaceutical research that makes NQR or NMR the only measurement methods practically applicable?

Analytical Chemistry

I am interested in ELSD, an HPLC detector.

Is there anyone who is currently using or has used this detector?

I would appreciate it if you could share information on the problems, concerns, and advantages of using it in real world situations.

It would also be appreciated if you could introduce, for example, review articles explaining the characteristics of quantitative measurements of analogous compounds without their standards.

I would like express my gratitude to everyone in this community.

I appreciate it.

Best regards,

For determination of water contents(moisture) spectrophotometrically.

Currently working on a USP assay method for HPLC that requires water-saturated butyl chloride as a mobile phase and water-saturated chloroform as a diluent.

What is the whole point of using water-saturated solutions like this?

Would there be alternative ways to substitute these solutions?

In analytical chemistry, a linear model is developed on multiple concentration levels with a goal to predict target analyte concentration in an unknown sample. Will the model prediction favorize a concentration if more calibration samples at that concentration level is used in the model development? I have not found literature article on this topic.

Is sample cleanup not a part of sample preparation. Are there any examples sample cleanup that are not sample preparation in analytical chemistry?

Hello everybody. Our instrument (i.e., ion chromatography) must stop working for more than 4 months because of some maintenance. My question is, during 4 months or more, does it need anything done for preservation? However, we have already removed the columns and are storing them in the refrigerator.

Thanks a lot

Couldnt find any for a long time…

I need a scientific gaps for those topic and I am doing it in an analytical chemistry lab

What is the difference between Principal Component Analysis (PCA) and Partial Least Square (PLS)? In which conditions is it better to use PCA over PLS practically, let's say in environmental chemistry or analytical chemistry? Or, even can we combine both methods? Thanks for your explanations.

How many grams of K2Cr2O7 to dissolve it in 1 liter Distilled water to obtain 50 ppm of Chromium? to become aqueous solution, Is there a specific equation to apply? Thanks

Ali

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Dear researchers,

I would like to ask you whether the retention of analytes of interest on the C18 column can be slightly affected by buffer concentration.

I have analyzed a mixture containing sulpiride (weak base) and diclofenac (weak acid) at 250 ng/mL on the C18 column with mobile phase A: ammonium formate and mobile phase B: methanol.

I have observed that when the concentration level of ammonium formate increased from 2mM, 5mM, to 10mM, the retention time of sulpiride slightly decreased from 6.72 min, 6.52 min to 6.46 min respectively, whereas that of diclofenac slightly increased from 10.04 min, 10.17 min to 10.28 min respectively.

As far as I am concerned, for a basic compound such as sulpiride, an increase in buffer concentration (ammonium formate) can result in a decrease in silanol activity so a positively charged compound such as sulpiride can have a slight loss of retention due to the ion exchange interaction between the compound and silanol group during a loading step. Consequently, the retention time of sulpiride was slightly decreased with an increase in buffer concentration.

However, for an acidic compound such as diclofenac, it is quite difficult to explain this phenomenon. In my opinion, it seems that when the concentration level of ammonium formate increases, the pH of the mobile phase slightly increases so the charged state degree of diclofenac slightly increases either. As a result, the energy configuration of diclofenac diffusing inside the pore of the C18 column is lower at a higher concentration level of ammonium formate (10mM) so it will have more interaction surface area with the C18 column, leading to more retention. However, this explanation seems not to be convincible because the higher charged state degree of diclofenac is, the more soluble is and the less retention is.

However, for the retention behavior of sulpiride and diclofenac, the above explanations are just my own opinion. Of course, I am not sure whether they are right or wrong.

If someone here can help me clear the retention behavior of sulpiride and diclofenac, I am really happy to listen to your valuable suggestions.

Thank you so much in advance,

Hello,

When working with methanol, I noticed that I could never take the exact volume of methanol with micropipette.

Is there any other tool or method that could solve this problem?

Many thanks for your concern,

application

Many methods call for reconstituting experimental samples in methanol/ water, but diluting the standards with some sort of plasma (typically blank bovine plasma). Why not dilute the standards in methanol/ water to match the experimental samples?

My peptide is Cholecystokinin (CCK8), MW=1142.35 (COOH-D-Y-M-G-W-M-D-F-NH2).

Stock solution in NH4OH 0.05M and working solution in acetonitrile.

I do MS infusion at conc. 500 ng/ml in acetonitrile.

I use two LC/MS machines: Micromass - Quattro Premier XE of Waters (Tamdem Quadrupole) and Applied Biosystems - API 3200 LC/MS/MS (triple quadrupole)

I run ES + but I can not see the peak at 1+, 2+, 3+,4+,...for [M+H], [M+Na], [M+K]

I wonder whether I have missed some other adduct ions that could be created during the ionization?

Or maybe my peptide is being degraded during preparing the sample?

Please give me some advice! Thank you!

Does someone have any practical experience with those columns?

The producer suggest ODS-B are more suitable for hydrophilic analytes, but without any concrete information.

Can they be used interchangeably with ODS-A columns? Are there expected changes in retention times of non-polar analytes? Are there differences in their pH tolerance?

Green analytical procedure index (GAPI) and National environmental methods index (NEMI) are assessment tools used for evaluating the greenness of an analytical method. Is there is any software through which GAPI and NEMI pictograms are constructed?

I am working on a project that requires the measurement of neuromelanin purity, and I have found papers that say that they have measured the purity, but they do not say how ( ).

Neuromelanin does not have a commercially available 100% standard, so I cannot do typical comparisons. Does anyone know where to begin or how to do the purity measurements?

Any help would be appreciated.

Thank you!

I'm a Chemistry student currently working on a thesis that involves phytoremediation of Lead in aqueous solution using a specific plant.

The FTIR results for both the stems and leaves of the plant after phytoremediation are almost identical, having the presence of O-H stretch and C-H stretch on both IR spectrum.

The FTIR result for the roots after phytoremediation, however, showed a possible trace amount of H2O at 3457.1 cm-1 (it was a tiny peak, therefore it cannot be called an O-H stretch), along with the presence of a C-H stretch and C=O stretch.

I need help in understanding what caused this deviation from the two other samples (stems and leaves). Could it be the presence of the metal in the root sample or are there any factors that I need to consider?

Thank you to anyone who'd be willing to give their insight/s on this, it would really help me a lot.

Hello

Laboratory techniques of biological and analytical chemistry to investigate the anticancer properties of plant samples.

thanks

Dear to whom it may concern,

I would like to kindly ask you about the ionization of acidic and salty forms of a given compound in electrospray ionization.

To be more specific, when I successively infused the reference standard solutions of atorvastatin in both its acidic (atorvastatin with an exact mass of 558.25) and salty (atorvastatin calcium with an exact mass of 1154.45) forms into the ionization source (electrospray ionization known as ESI) of the mass spectrometer, I always obtained the same precursor ion (m/z 559.5 in positive mode) of its forms.

I do not understand the reason why the atorvastatin calcium could show the same precursor ion as that of the acidic form of atorvastatin.

May you please give me an explanation of how the salty form of atorvastatin is ionized in ESI, resulting in the same precursor ion as that of the acidic form of atorvastatin?

Thank you so much.

Best regards,

I want to quantify the chromium in solution. I want to know whether atomic adsorption spectroscopy is better or UV vis spectrophotometer.

According to the pourbaix diagram of Fe(2+), it should be dissolve in pH<6, but it is solid even in pH=1. I realy dont know what is the reason.

I am looking for a method to completely remove proteins from plasma without using heat or adding salt ions. I have considered using activated carbon, but I am unsure if this is feasible. Are there any other effective methods for achieving this goal?

Chemical Informations

In the Column treatment of aqueous solution of Chromium Removal by Adsorption

Hello, I am a student in analytical chemistry, I am supposed to prepare samples, quality control, and calibration serial dilution for a forensic project which is working on larvae and flies (for quantification of benzodiazpines).

would you please correct what I wrote here even in terms of the specific volume and concentration?

I have powdered diphenylcarbazide and I want to make 0.5% w/v solution of diphenyl carbazide. Since it is dissolved in acetone.

Does it mean 0.5 g in 100 mL acetone? Is there any need to add distilled water?

In literature it is prepared by dissolving in acetone and then 200 mL distilled water was added.

Thanks for your guidance

I want to deacetylate the chitosan in sodium hydroxide (50 % w/w) solution. Does that mean 50 g NaOH in 50 mL of distilled water? What should be the appropriate time and temperature for the complete process? There are different temperatures and times are reported in literature.

Thank you for your help!

I made several reactions with 3,5-Dinitrobenzoyl chloride. When I looked at similar reactions for this substance, no heat was ever given in the reaction (even though heat increases the yield).

The interesting thing is that this substance turns black as soon as the heat is given to the reaction environment. Due to the fact that, theoretically, the polymerization of this material is impossible. Do you know the reason why they do not give heat to this material?

Hello everyone,

I want to calculate a ratio, but for some measurements, I have <LOD in the denominator

There is actually a range of possible numbers <LOD

One solution could be to consider: =LOD, or LOD/2, etc. ?

Are there methodological references which I can confront?

Thank you in advance

Hello everyone,

I want to calculate a ratio, but for some measurements, I have <LOD in the denominator

There is actually a range of possible numbers <LOD

One solution could be to consider: =LOD, or LOD/2, etc. ?

Are there methodological references which I can confront?

Thank you in advance

Hello

I have received the FTIR graph after the analysis of the sample but the graph isn't aligned to the baseline. I am attaching the file. Kindly guide me is it the sample or machine error?

We are looking for a way to identify the composition of a polymer blend that we do not know the composition. The composition is based on a polyurethan polymer, silicone elastomer, polyester-based polymer, and enzyme (that we know).

We have done some research and it seems that FTIR combined with TGA (Thermogravimetric analysis) can possibly be helpful for polymer blend identification.

We hope that our colleagues can share their point of views on how to approach the situation and suggest any helpful tools that can help us.

Thank you in advance.

Is it necessary to carry out validation tests on model mixtures prepared using both substances, or is it enough to use one substance for testing?

What validation tests should be carried out for an "alternative" substance only? If there is a quantitative method: what validation tests should be checked, for example?

Is it necessary to use a risk-based approach to determine validation tests when registering a new alternative substance during revalidation?

I'm really looking forward to your response, thank You for your attention!

Hi All,

We are trying to add Magnesium & Strontium dopants to our Beta Tricalcium Phosphate (b-TCP) powder. Recently, we obtained EDS data on the undoped b-TCP and doped b-TCP to see if the investigate if the doping was successful. However, we are observing higher weight percentages of the Magnesium dopant in the undoped b-TCP and we can't figure out why we are observing this trend. After we first observed this, we have used EDS to look at multiple different samples but they are all showing similar results. We have contacted the manufacturer of the pure, undoped, b-TCP powder and they agree that we should not be seeing this. We are pretty confident that we don't have contaminated, undoped, pure b-TCP powder. But we still aren't sure what might be causing these results. The attached Mg Map Data is from the undoped b-TCP only but the spreadsheet shows some examples of the weight% values we are observing.

Does anyone have any ideas that might explain the results? Are there any recommendations for how we can discriminate between potentially overlapping signals that might be giving false Mg signals?

Thanks!

LOD and LOC can be calculated from the calibration plot. One of the ways to do it is:

LOD = 3 SD(intercept)/S

LOC = 10 SD(intercept)/S

Where SD is the standard deviation of the intercept and S is the slope.

However, I have seen that standard error (SE) is often used instead of SD. But, SE is not the same that SD:

SD = SE*(N)^1/2

Thus, LOD and LOC from SE should be less than LOD and LOC from SD. However, I used SE for my work because I noticed that when I used SD, LOD and LOC were very high.

What do you think about using SE and SD for LOD and LOC estimation?

Hello, I am a student investigating acetate ions in wood.

My current mobile phase is 1000:0.5 (H2O;H2SO4) and I do not have the most resolute peak for acetate. The column is a H+ Column packed with sulfonated styrene /divinylbenzene copolymer backbone. What is a mobile phase worth trying?

pH mobile phase currently is ~2.0

pKA acetic acid is 4.76.

Analyt is acetate in NaOH with a basic pH.

Also is a buffer useful, if so which buffer is needed for acetate ions?

I trying to analyze EPDM using pyrolysis gcms.

Does anyone know where I can get the standard reference materials?

#Analytical Chemistry #Veterinary Drugs #Residue Analysis of Pesticides #LCMSMS

Hello,

In the chromatogram you can see that the second peak (retention at 4 min), which is an acetate peak, has huge tailing which is known for the sample that is measured but I need to know how I can separate the component that causes the tailing.

My mobile phase is MilliQ/H2SO4 (1000;0.5) using an H+ Ion exchange column with UV detection. Method uses a flow rate of 0.8 ml/min with a column temperature of 40 degrees for the first 8 minutes.

thanks in advance on sharing the method

We are trying to determine the UV-visible spectrum for some hydroethanolic herbal extracts but we keep getting negative reading, we tried dissolving the samples in different solvents, distilled water, 5% propylene glycol and 10% propylene glycol, but the results are always negative, what could be the reason? and is there a solution for this problem?

Tannic Acid Modification.

I am searching for journals that publish reviews of books on spectroscopy, including analytical chemistry, computers in spectroscopy, and signal processing in spectroscopy.

I want to estimate freezing point of a mixture made from Ehhanol (H₃CCH₂OH, MW: 46.07 g/mol) , mono propylene glycol (CH₃CH(OH)CH₂OH, MW: 76.1 g/mol) and water. And the ratio of the mixure will vary for example I can start with 1:1:1 and so on. I spent couple of week to google it but not able to figure out how to do that. If someone here have some experience with it or have some suggestion / literature then please help to solve for this problem.

I have prepared quaternized PVA. I want to measure the degree of substitution of quaternized polymer by titration. In literature, potassium chromate is mentioned as an indicator but I have potassium dichromate in my lab. Can I use this salt instead potassium chromate? AgNO3 solution is used for the titration.

Thanks for your help.

Let's start a discussion: What do you consider are the key factors or conditions to develop voltammetric and amperometric sensors with a good analytical performance.

Dear All,

I'm looking for a suitable and a simple software of Chemometrics technical,

as effective tools for application in exploring chemical data in analytical chemistry, what do you recommend for beginners?

Dear Researchers :

I have this question and I have an hypothesis:

Why Natural HDPE, when extruded at temperatures about 100 °C (around) it has a white (but pale white), and then when the polymer cools down it color turns between white an yellow.

I understand that this phenomenon it is a general case of all LLDPE, LDPE and HDPE , and in all fabrication processes : Extrusion, injection, molding, pressing, etc.

So this is fundamentally, a chemical characteristic of the material ...

It has to do with a change in the Oxygen concentration in the material ?

Thank you all in advance,

Best Regards !

For chemical characterisation of my biochar samples & in order to understand it’s chemical composition better I need pyrolytic-GC/MS data of my samples, from which institute i can get this facility also i would appreciate it if anyone can share me the link.

After ultrasonic extraction of non-freeze dried sediment samples with n-hexane, can it be directly purified by c18 solid-phase extraction? Why?

Can it be purified directly with a silica gel column? why?

Any known about these two question

Analytical Chemistry

I need to prepare SRM from the benzoate solution to be used for calibration.

I need to know the best type of bi-potentiostat instrument?

Do you think it is appropriate to use a photoelectrocatalytic amperometric sensor also as a voltammetric sensor?

Hi everyone, I have a question regarding the determination of dissolved aluminium by colorimetric method using pyrocatechol violet according to ISO 10566:1994. In the preparation of 'mixed reagent', we have to add 5 mL of the aluminum standard solution (10 mg/L) into 100 mL of this mixed reagent (total volume).

My question is:

- What is the role and function of the addition of standard solution for this method? In this standard it only says "accurate addition of the aluminum standard solution is essential in order to allow a linear calibration at low concentrations".

Note: if we calculate the concentration of this aluminium standard solution in the sample is about 15 µg/L.

Thank you for your answers.

The fate of nanodrugs / nanoparticles in vivo draws a lot of attention, and many studies label fluorescent of nanodrugs / nanoparticles in order to disclose their distribution in vivo.

- What are its advantages and disadvantages ?

- Is it a reliable tool ?

I find there are various kinds of diffusion coefficient equations, and there always exists the deviation, so can anyone introduce me some good methods for calculating the diffusion coeffients for gasphase species  with higher precision. Thanks again.

Hi, I'm working on my bachelor's final year thesis which is based on being able to detect the presence of saliva in crime scenes. My first step was to confirm that with the settings I have I am able to detect the presence of tryptophan. This was a 0.5g in 100ml solution of 5mM KCL and 2ml of this was placed in a cuvette and scanned for, which was successful - it result in an emission peak around 350nm.

I further tested swabbed dried saliva with a PBS swab off a lab-grade glass slide and placed it in a cuvette with 2ml of 5mM KCl and ran the tests. The results were way off the intensity scale.

So I tested for the range of dilutions to see in what range the readings wouldn't go off the scales, and dilutions of 1 in 100, 250, 500 and 1000 seemed to have worked. But unfortunately, the intensities of all of these were varying there was so linear relation like one would expect since its decreasing dilutions. I decided that I'll perform my tests from scratch and zeroed the instrument with KCl since that's what my samples are diluted in, and then ran the control again to see if any peak appears (since if you zero the instrument with a certain chemical, if you scan for it, nothing should appear), and a peak showed.

I then contacted Agilent hoping they'd be of some help. They said I was overloading/maxing out the detector, which I am unable to understand since I have diluted this to a small amount. And from previous papers that have performed similar experiments, they haven't needed to even dilute their samples.

I then tried varying the settings such as the PMT voltages, emission and excitation slits and performed tests with tryptophan to see if the peak at 350 would be detected. And failed as all the resulting peaks turned out to be "below threshold".

I am unable to determine how to go about it, and I'm nearing the deadline for working in the lab and I'm nearing the end of all options.

Obviously, since this is the first thesis I'll ever be writing I'm afraid I won't have results and just have various different trial and error methods.

All suggestions and any help I get will be really helpful.

I will be editing this post to add images of the settings I have my instrument on just for extra information. And for reference, I'm using the Cary Eclipse Agilent Fluorimeter with the Scan application.

Thank you in advance. :)

Shaina

I'd like to prepare a stable, cheap solution of bromine for small-scale qualitative detection of alkenes in biological samples. Bromine water is commonly used, but for my purposes it'd be better to have bromine in some organic solvent. However, bromine will react with many common organic solvents, like ethanol or acetone.

Please, could anyone suggest organic alternatives to bromine water for alkene detection?

Thanks in advance.

We know, that we can use only validated methods for comparative studies. In our lab we have performed the validation of the dissolution method for the specific medicine. In the comparative study we used several different media, these media did not participate in our validation, exept the one for quality control. Does it mean that we have to perform full validation procedures in each media additionally?

In biodiesel production through transesterification, various of heterogeneous catalysts could be utilized. However, each heterogeneous catalysts are showed different yield. My question is What are the factors of heterogeneous catalyst that affect their activation during transesterification?