Purchasing an Instrument

To some of us it can unexpectedly happen that we are faced with the task of having to buy a mass spectrometer, eventually for ourselves or on behalf of someone else. References to certain commercial instruments made in this chapter were in no way intended to preclude such a 100,000-600,000 decision. The below guide may be useful in selecting an instrument that meets your requirements best  

Molecular Analysis by Mass Spectrometry. Science 1979, 205, 151-159. 

Bninnee, C. The Ideal Mass Analyzer Fact or Fiction Int. J. Mass Specirom. lonProc. 1987, 76,125-237. 

Beynon, J.H. Instruments, in Mass Spectrometry and its Applications to Organic Chemistry, Elsevier Amsterdam, 1960 pp. 4-27. 

Habfast, K. Aulinger, F. Massenspek-trometiische Apparate, in Massenspek-trometrie, Kienitz, H., editor Verlag Chemie Weinheim, 1968 pp. 29-124. 

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In the single wavelength detector, 254 nm and 280 nm are strong lines from the mercury source and hence, are selected in most comnercial instruments. Of the three types of U.V. detectors, this one gives the lowest noise level (down to 0.00002 O.D.), but, of course, some flexibility is lost in not being able to work at other wavelengths. Nevertheless, when one purchases an instrument, this is the first detector selected. 

Cost Another consideration is the cost of the method being considered. This could be the cost of consumable supplies (reagents, solvents, etc.) or capital equipment if purchasing an instrument is an option. The cost of using an outside lab must also be weighed. The cost of the measurement plus the number of samples (above) can be significant factors, especially for an on-going need. 

Attempts have been made to replace the Blue or Wool Scale by physical devices that measure the radiation of the light source. To determine the radiation of a given light source, the irradiance (in W/m2) is multiplied by the exposure time (in s). The equipment necessary to carry out such measurements is commercially available. Measurement in the UV region would be desirable. It has recently become possible to purchase an instrument which can measure spectrum-related irradiance in the important UV range. 

Vendor s reliability. The vendor that supplies the instrument should have a track record of providing high-quality instruments and after-sale support. A vendor audit should be conducted for a new instrument supplier to evaluate the company s ability to build high-quality products. Purchasing an instrument from a financially unstable vendor is risky. 

Instrument control typically is limited in commercial instruments to the extent that non-routine uses of the instrument for development purposes may be difficult. The data acquisition software is not always optimized for isotope ratio measurements. These issues should be considered when purchasing an instrument for work that includes both production and development. 

Once basic requirements and secondary objectives have been established, the prospective purchaser will find it easier to discuss details with sales representatives. From the latter s viewpoint, it is easier to talk to a potential customer who knows what he needs from a mass spectrometer system rather than to a customer who has only a vague idea of what is required. In fact, an uninformed customer can end up purchasing an expensive instrument that is far too good for the analyses required or, at the other extreme, a cheap instrument that is inadequate for immediate needs, let alone ones that might arise in the near future. 

Standard reference material (SRM) for wavelength accuracy, stray light, resolution check, and photometric accuracy can be purchased from NIST. Certified reference materials (CRMs) which are traceable to NIST and recertification services can be purchased from instrument manufacturers and commercial vendors [12]. The cost of neutral-density filters and prefabricated standard solutions in sealed cuvettes can be substantial. When purchasing performance verification standards from a secondary supplier other than a national standard organizations such as NIST in the United States and National Physical Laboratory (NPL) in the United Kingdom, make sure that the traceability of the standards are available in the certificates. The traceability establishes the relationship of individual results to the national standard through an unbroken chain of comparisons. 

However, HPLC is not without its drawbacks 1) equipment cost is very high (thus small processing operations would probably be unable to purchase and maintain such an instrument) 2) only one compound can be measured at a time since different columns and solvents are used for each class of compounds (this also means that time must be spent in changing the system from one analysis to the next) 3) pre-purification is required and for good resolution repeated liquid-liquid and evaporation steps are involved 4) the procedure is slow (only 10-15 samples can be processed per person per day) 5) it is sensitive only to the parts per million (ppm) range (pg/gm). Thus, in summing the current status of limonin and naringin quantification, a quotation is most appropriate. 

Some people feel that columns cost too much and, therefore, purchase the lowest-price column. This is one strategy for choosing the best column. However, when the nature of a column in a chromatographic system is considered, it makes sense that there should be little to no price sensitivity in the user. For instance, if an instrument sells for 20,000, a typical column sells for 300. Therefore, a column is only 300/ 20,000, or 1.5% of the cost of an instrument installation. This is a minor part even if repeat buying is calculated. Second, keep in mind that without the column performance the entire instrument is worth precisely zero. Third, it is very hard to evaluate how a column will perform without prior experience with it—there is no easy believability to competitive claims that one C 8 column will work as well as, or even the same as, another. In essence, a column is nothing more and nothing less than a user s attempt to solve an analytical problem. Users should not be sensitive to price, they should be concerned with time, effort, and repeatability. Therefore, most individuals should gladly pay for these benefits, because the best column does your separation. 

Background interference. Correction for non-specific absorption is sometimes essential in geochemical work (section I.D.) and is most conveniently carried out by means of a continuum source. However, not all systems available are completely effective, and this feature should be checked before purchase of an instrument. It is essential that the beams from the hollow-cathode lamp and the continuum lamp traverse exactly equivalent paths through the flame, and can be accurately balanced for energy. 

The next step is either to select an existing system for the analysis task or to pnrchase a new system. When a new system is purchased, it is often purchased not just for a specific analysis but also for use in general applications in the laboratory. In this case, the Reqnirements Specifications should include a representative mix of the anticipated applications, and the FSs shonld be set such that the instrument can handle all of the requirements. Next, the nser shonld look for an instrument on the market that best meets these requirements. If the selected system does not provide all of the fnnctions — for example, regarding software — the user can decide whether to develop these himself or ask the vendor or a third party to do so. 

Sample 6410 appeared to be a failed synthesis, with little detectable peptide. Sample 7818 was quite pure, but had no correct product, since Gly had been substituted for Glu in the synthesis. The laboratory submitting sample 7818 used an instrument with amino acid cartridges that were refilled with bulk amino acid derivatives. Although it is not known whether the refilling procedure was carried out in-house or by a commercial supplier, this type of opportunity for a mistake could affect many peptide syntheses, and should be a cause for concern in all laboratories. Sample 8246 contained a large quantity of peptide missing the C-terminal Tyr. From the description on the protocol sheet, it appeared likely that this laboratory had prepared its own Tyr-resin. Yet purchase of preloaded resins provides no assurance of quality. 

The annual cost of equipment includes depreciation and maintenance. In addition, an allowance should be made for the loss of interest which, if the instrument had not been purchased, would have accrued from investment of the capital. Depreciation is the difference between the capital cost and the secondhand value. In practice, the secondhand value of an instrument is usually small, not because it is worn out, but because there are newer and better instruments available for performing the same task. Few instruments cannot be replaced by faster and better ones after 5 years, although many continue to be used for long after this time despite progressively increasing maintenance costs. This built-in obsolescence makes rental attractive as this enables the user to change his instrument quickly without loss of capital it may also act as an incentive to manufacturers to improve their maintenance service. 

The first true compaction simulator capable of mimicking the compaction and ejection cycle of a rotary tablet press was reported by Hunter et al. in the 1970s (2), The evolution of such an instrument presented a novel tool for both powder compression research and scale-up of the tableting process. Celek and Marshall report that although compaction simulators are expensive to purchase, they present the following attributes ... 

One underlying principle to be followed in purchasing a NIR instrument that should be adhered to is simply this first determine your application, then purchase an appropriate instrument [1]. All too often an analyst is enamored by a particular piece of equipment and purchases it, and, then looks for an application. This is a proven formula for failure. As a rule of thumb, the particular application should be clearly defined and specific objectives identified. Its vital steps must be identified and the location of the test determined (in-line, at-line, or in the laboratory). At that time, instrument manufacturers should be contacted, feasibility studies conducted, references checked, and reliability of any instrument determined. Then and only then should an instrument be purchased. Most instruments available today will be suitable for a variety of applications, but choosing an inappropriate instrument for a particular application surely dooms the analyst to failure. Analysts will often erroneously assume that NIR is at fault in such situations, rather than consider that they have selected an improper instrument. 

Evaluation of the performance of a method or an instrument represents the largest use of CRMs. Examples are widely reported in the literature. One could even say that the development of a new method or instrument without evaluation of the performances with (a) CRM(s) is an incomplete task. Besides these research tasks, CRMs for calibration or validation are also used to assess the performance of instruments by the manufacturer himself to demonstrate the possibilities of his instrument or by the customer who wishes to evaluate the proposed instrument before purchasing it. CRMs produced by independent official or regulatory bodies to validate instrument performance or calibration sets have been under development for several years. They have in particular allowed the solution of inaccuracy problems in the biomedical sector where calibration test kits of automatic instrument manufacturers were not comparable and even led to different results between countries such arguments supported many BCR projects for... 

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