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News from the Lab
New Catalog
Inorganic Ventures' new 2006-2007 catalog of inorganic standards and custom solutions is now available. Request your copy today:
Online Request Form »
PittCon 2006
We'll be at PittCon 2006 in Orlando, FL (March 13-16). If you're attending, drop by booth #2858 and say hello. We'd love to see you!
Analytical Insight
Ever wonder why Nitrates can't be determined via ICP-OES?
ICP-OES is capable of seeing 'Nitrogen.' It sees nitrogen in all of it's oxidation states and chemical forms the same way, i.e. as nitrogen (N). The problem is that we work in an atmosphere that is 80% nitrogen. If we could eliminate all of the nitrogen background and only have the nitrate-N going through the plasma, then we would be able to determine Nitrate using ICP-OES.
Constructing a Sampling Plan
A synthetic organic chemist will construct a plan by working backwards from the final product. A similar approach may work well for the trace analyst. Start by examining the following basic information:
- The analyte(s) of interest.
- The required detection limit(s).
- The uncertainty requirement(s).
- The chemical composition (matrix) of the sample.
- The quantity, availability, and history of the sample.
Much of the above list can be determined based on information gathered while defining the problem. In most cases, analytical resources are available in-house to address the problem. For example:
- The basic information listed above is sufficient to determine whether publications or information is available in your reference library. Always start with a search of the literature.
- The identity and detection limit requirement of each analyte indicates the analyte measurement technique(s) required and the amount of sample required.
- The uncertainty requirement indicates the number of measurements, assuming there is sufficient sample available.
- The chemical composition of the sample, together with the identity of the analyte(s), indicates possible sample preparation routes.
- The identity of the analyte(s), together with the detection limit requirement(s), indicates the degree that contamination issues should be considered. This determines the need for analytical blanks and special apparatus or a clean area / room.
- The sample composition indicates potential interference issues.
- The sample composition or type indicates the uncertainty to be expected form the sample collection and/or the need to develop a sampling procedure and to determine sampling uncertainty. For example, the sample may be the only "world's supply", negating the need for a sampling procedure.
- The estimated sampling uncertainty can be used to define the analytical measurement precision (i.e. -- reducing the analytical error to less than one third of the sampling error serves no purpose).
The basic information can provide the analyst with potential analytical measurement technique(s), suspected interferences, contamination issues, and the number of sample measurements required per determination (measurement refers to a complete analysis including sampling, preparation, instrumental analysis and reporting the final result and uncertainty). At this stage of the planning process, the analyst can determine if a certified reference material (CRM) should be obtained for method validation. In addition, the chemist can approximate the need for analytical reagents and apparatus and/or calibration standards.
Lastly, estimate the time and cost of the project and base your initial approach on these estimates. Remember, there is always the possibility that more than one iteration may be required before an acceptable approach can be developed.
Exceprt from Inorganic Ventures' Reliable Measurements Guide.
XRF vs. ICP for Concrete Metals
Which instrument is more accurate for analyzing metals in concrete: XRF or ICP? Paul offers some insight.
ICP Operations Guide (complete)
A clear 16-part online guide intended for anyone preparing samples and standards for measurement using ICP. Topics cover many day-to-day tasks required by all operators.
Reliable Measurements: A Guidebook for Trace Analysts (complete)
An essential 17-part online guide for chemical analysts. Topics cover all phases of sample collection, preparation, measurement, and data analysis.
Q: What's a veterinarian's idea of a catalyst?
A: 1) Siamese
2) Tabby
3) Persian
4) Calico
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| Elemental Spotlight |
Sulfur
Storage & Handling: Keep tightly sealed when not in use. Store and use at 20 ± 4°C. Do not pipet from container. Do not return portions removed for pipetting to container.
Chemical Compatibility: Soluble in HCl, HNO 3, H 3PO 4, and HF aqueous matrices, water, and NH 4OH. Stable with all metals and inorganic anions at low to moderate ppm levels under acidic conditions, except Ba, Pb, Ca, and to a lesser extent Sr.
Stability: 2-100 ppb levels - stability unknown - in 1% HNO 3 / LDPE container. 1-10,000 ppm solutions chemically stable for years in LDPE container.
S Containing Samples (Preparation & Solution): We most often get questions about the determination of S in rocks, silicates and insoluble sulfates (the finely powered sample is fused in a Pt 0 crucible with 6 times its weight of Na 2CO 3 + 0.5 grams KNO 3. The fuseate is extracted with water. Any BaSO 4 present in the sample is transposed by the carbonate fusion to the BaCO 3, which is left behind in the water-insoluble residue. If PbSO 4 is present, the fuseate should be boiled with a sodium carbonate saturated with CO 2 solution for 1 hour or more. The PbSO 4 will be transposed to the water insoluble carbonate which can be filtered off. Boiling the fuseate with a saturated carbonate solution is good insurance for samples containing Ba, Sr, and Ca. The Ba, Pb, Sr, and Ca free filtrate can be acidified and measured by ICP).
Excerpt from Inorganic Ventures' Analytical Periodic Table: Includes detailed analytical data for more than 70 elements.
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