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Home > Newsletter
2nd Quarter 2000 - Vol.8, No.2 - Circulation 4471 - Editor: Eric W. Lindsay |
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Home > Newsletter
2nd Quarter 2000 - Vol.8, No.2 - Circulation 4471 - Editor: Eric W. Lindsay |
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In This Issue: Formaldehyde by GCMSMetals Screen by ICPMScGMP - Quality AssuranceWCAS - Our Core ValuesLaboratory Tidbits |
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Formaldehyde by GCMSMany methods have been developed over the years to measure formaldehyde. Currently, we typically use HPLC to determine formaldehyde after derivatization with 2,4-dinitrophenyl-hydrazine (DNPH), which forms derivatives with aldehydes and ketones. This method is sensitive (detection limit in water is approximately 6 ppb) and relatively specific, since the derivative has an absorbance maximum at 360 nm. Although interferences are greatly |
reduced at this wavelength, they are not eliminated entirely. Other colored compounds, though chemically unrelated, may interfere with the formaldehyde peak. In these instances, GCMS can be used as a confirmatory technique. For GCMS, the derivative is extracted from aqueous solution using a suitable solvent, such as toluene. Although the GCMS method lacks the sensitivity of the HPLC method (detection limit approx. 1 ppm), the use of a mass spectrometer for detection allows positive identification of the formaldehyde-DNPH derivative (see Figure). |
| Other carbonyl compounds, such as acetaldehyde, propionaldehyde, acrolein and acetone, have also been detected using this approach, and many other compounds may also be amenable. |
If you have any questions about formaldehyde, and whether GCMS may be able to solve your specific problem, give Mike Shelton a call at extension 702.
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Metals Screen by ICPMSInductively coupled plasma-mass spectrometry (ICPMS) can be used to screen samples for metals contamination. In a typical scan of a sample in solution, data may be collected for masses 5-250 amu over a 1-2 minute period with sensitivity in |
the sub ug/L range for most elements. This means that the concentration of more than 60 elements can be determined quickly. Using this technique, WCAS offers a test which we call a "Metals Screen" to measure the concentration of over 60 elements in a sample. An example report appears below: |
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More than 60 Elements |
Sample: Acid Leachate Metals Screen Report Inductively Coupled Plasma - Mass Spectrometry
Date Analyzed: 2-18-97 Elements Not Analyzed: All Gasses, C, P, K, S, Si, Sc, In, Tb |
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25 of the more common elements fully quantitated (in blue); others estimated +50% but can also be quantitated on request |
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Detection Limits will depend on sample preparation |
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Detection Limits based on blanks |
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Alternative techniques provide lower detection limits: HG-ICPMS, preconcentration, etc. |
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Includes Uncommon Elements |
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GFAA also available for some elements |
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Isotope Ratio Analysis Available |
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Isotope dilution techniques for lead provide very accurate results |
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Elements not included: Sc, In, Tb used as internal standards |
How's it done?In a typical test, a sample is put into solution usually by digesting or diluting in acid. The sample solution is spiked with known concentrations of three elements (usually Sc, In, and Tb). Standards of common elements, blanks, and the sample solution are then introduced to the ICPMS The element concentrations in the samples are then determined one of two ways: (1) for the elements that are in the |
standards, the elements are determined quantitatively (within 15% for most) or (2) for the elements not in the standards, the elements are estimated (within 50%) by comparison with internal standard responses. Unlike many other spectroscopic techniques ICPMS has a fairly uniform response, so fairly accurate estimates can be made. For more information on the analytical technique, click here. |
ProsSince each element has a unique isotope mass, interferences are usually minimal. Since detection limits are in the sub ug/L range, even tiny samples (1-10 mg) can be analyzed with excellent detection limits. This is a very efficient way to test expensive or rare samples like synthetic peptides or proteins, or even samples from ancient artwork. |
Only 2-5 mL of sample solution are needed. Usually a minimum of 10 mL is requested so that duplicates, spikes, and dilutions can be analyzed. Do you suspect metals contamination is causing a problem with your product? This is an excellent method for solving this problem. Some non-metallic elements are usually reported using this method: Br, I, and P. |
ConsHigh concentrations of elements that are predominant in the sample can cause interferences for other elements. These are usually elements of neighboring masses, oxides, halides, argides of some elements, and doubly charged ions. For example Ca based products have an interference for Ni from CaO, and carbon based samples have an interference for Cr from ArC. All of these potential interferences are considered and flagged in your report. Some elements have reduced sensitivity and higher detection limits, the most problematic being iron (Fe). Because the plasma has a background of argon oxide (ArO, mass 56) which is an interference for the most abundant 56Fe isotope, the less abundant isotope |
57Fe is used,
leading to reduced sensitivity and higher detection limits (20-100 ug/L).
One alternative for Fe is graphite furnace atomic absorption (GFAA),
however this is not very advantageous since GFAA has a detection limit for
Fe of about 10 ug/L coupled with many more potential interferences and experimental
difficulties.
Some elements are not determined by this technique: gaseous elements, C, S, F, Cl, and the internal standard elements that are spiked (usually Sc, In, and Tb). Some samples are very difficult to place in solution (e.g. silicates). Alternatives such as emission spectroscopy or X-ray fluorescence which do not require solutions may be considered. |
cGMP - Quality AssuranceWCAS complies with FDA cGMP regulations as a quality control laboratory for pharmaceutical manufacturing. FDA has audited our facility twice in the last four years. We encourage our clients to do the same. In fact, we average about 2 audits per month by pharmaceutical clients. In addition, our laboratory can comply with FDA and EPA GLP regulations, but this requires some planning prior to starting a study. To comply with cGMP, our quality control (QC) operations are conducted by the analysts performing the tests. QC consists of meeting suitability criteria, preparing and analyzing blanks, duplicate and spiked samples, reference materials, and several other things. Quality Assurance is provided |
by a separate oversight group. Results which are out of product specification are investigated prior to recommending re-sampling and/or re-testing. Instruments are qualified during installation and annually during operation, and calibrated routinely for NIST traceability. Analysts are trained in cGMP regulations and standard operating procedures (SOPs). SOPs are reviewed and/or revised annually. All this is well documented, and the documents are controlled by QA personnel. Prior to conducting an audit, we encourage our clients to review various documents on our web site including our QA Manual, FDA 483 and response, some SOPs, a list of accreditations, directions to the lab, and hotel accommodations. |
WCAS - Our Core ValuesAny company worth its salt needs to think hard and long about what their core values are. Without core values that are both meaningful and understood by everyone, a company may be doomed to failure. We believe in the following: |
Honesty Safety of our Employees and Community Good Science Fairness Quality |
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WCAS has purchased a new GCMS! We received our third HP (now Agilent) 5973 GCMS on March 28. After a smooth installation and qualification, we were off and running! The addition of this instrument should allow us to improve our turnaround time and dedicate more time to development of new methods, such as assaying active ingredients in botanical preparations. WCAS has always been the lab for solving unusual problems; if you have a problem where GCMS can help, give us a call. |
We’ve redesigned our web site with help from a design firm. Our home page is shown to the left. We believe this to be easier to navigate through. Any comments from you would be appreciated. Just email Jack at jackn@wcaslab.com. Our web site can be found at or
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Quick QuotesA person who has had a bull by the tail once has learned 60
or 70 times as much as a person who hasn't. He that would govern others, first should be the master of
himself. |
Advice is less necessary to the wise than to fools, but the
wise derive most advantage from it.
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9240
Santa Fe Springs Rd |
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562.948.2225 Fax 562.948.5850 |
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