Sample preparation internal standard

International Standards Organization (1996), ISO 4661, Chemical Tests for Raw and Vulcanised Rubbers, Part 2, Sample Preparation, International Standards Organization. 

Whilst for the analysis of plant material for cannabinoids both GC and HPLC are commonly used, in analytical procedures the employment of GC-based methods prevails for human forensic samples. Nonetheless, the usage of HPLC becomes more and more of interest in this field especially in combination with MS [115-120]. Besides the usage of deuterated samples as internal standards Fisher et al. [121] describe the use of a dibrominated THC-COOH (see 7.5). The usage of Thermospray-MS and electrochemical detection provide good performance and can replace the still-used conventional UV detector. Another advantage in the employment of HPLC rather than GC could be the integration of SPE cartridges, which are needed for sample preparation in the HPLC-system. 

Although laser ablation usually dispenses with the need for sample preparation in the analysis of rocks, the use of a major element of the sample as internal standard requires the prior knowledge of its concentration also, the addition of an internal standard element to a rock sample is difficult. Fusion of the sample with Li,B407 allows the use of Li and B as internal standards. Linear calibration graphs (constructed from standard reference geological materials) have thus been obtained for Al, Ca, Fe, K, Mg, Na, Si and Ti, and relative standard deviations of 1-2% n = 12) achieved. 

Quantitative analysis is normally performed by preparing calibration curves using external standards. To compensate for instrument drifts, instabilities, and matrix effects, an internal standard is usually added to the standards and to the sample. Multiple internal standards are sometimes used to optimize matching of the characteristics of the standard to those of various analytes. 

Quality control of the GC data is very important and for atmospheric sampling, an internal standard should be used to check on recoveries and the performance of the sampling equipment. A suitable compound for atmospheric work is anisole. A known concentration dissolved in methanol should be injected into the adsorption tube before sampling is started. The method is standardized by sampling a prepared standard atmosphere. 

Emission spectroscopy is widely used for both qualitative and quantitative analysis. The high sensitivity and the possible simultaneous excitation of as many as 72 elements, notably metals and metalloids, makes emission spectroscopy especially suited for rapid survey analysis of the elemental content in small samples at the level of 10 /ug/g or less. With control over excitation conditions to maintain constant and reliable atomization and excitation, the spectral line intensities can be used for quantitatively determining concentrations. An analytical curve must be constructed with known standards, and often the ratio of analyte intensity to the intensity of a second element contained in, or added to, the sample (the internal-standard method) is used to improve the precision of quantitative analyses. Preparation of standards for arc and spark techniques requires considerable care to match chemical and physical forms to the sample this is not commonly required for ICP discharge. 

A known quantity of an internal standard can be injected along with known amounts of the compound of interest. The area versus concentration is calculated to crate a calibration curve. Then an appropriate quantity of the internal standard is added to the raw sample prior to any sample analysis. The peak area of the standard in the sample run is compared with the peak area when the standard is run separately. This ratio serves as a correction factor for variation in sample size, losses during sample preparation, or incomplete elution of the sample. The internal standard must be completely resolved from adjacent sample components, should not interfere with the sample components, and should never be present in material to be analyzed. 

The most witlely used quantitative method of ICPMS uses a set of calibration standards for preparing a calibration curve. Simple aqueous standards are usually adequate if the unknown solutions are sufticiently dilute — less than 2000 pg/mL of total dissolved solids. With higher concentrations of matrix elements, attempts are often made to match the matrix elements in the samples with those in the standards. To compen-.sate for instrument drift, instabilities, and matrix effects, an internal standard is usually introduced into the standards and the unknowns. The internal standard is an clement that is absent from the samples and that has an atomic mass and ionization potential near those of the analytes. Two elements frequently used for internal standards are indium and rhodium. Both produce ions in the central part of the mass range ( In, "In, and " Rh) and are not often found naturally occurring in samples. Generally, log-log plots of ion current, ion count, or intensity ratios for sample and internal standards are linear over several orders of magnitude of... 

Read the apparent concentration of biotin from the radioactive count obtained from each sample from a calibration curve prepared with each batch of samples as described in Section G below. Let this concentration be A m/iig biotin/liter. Read the apparent concentration of biotin in the flask (containing sample plus internal standard) which was taken through the analysis with each sample. Let this concentration be B. mfig biotin/liter. Calculate the concentration of biotin in the sample from the expression ... 

With each jmej of samples being bioassayed prepare 7 flasks containing 20 ml of vitamin-free sea water enriched with the nutrient solutions as described in F.2. To one flask make no addition, and to the other six flasks add 0.1 ml of solution B-G, respectively. The concentrations of added B in the sea water of the external standard series will be 35, 25, 20, 15,10, and 5 m/ig B iiter, respectively. Inoculate and incubate these standards as described in Section F.3-6, along with the samples being bioassayed. Prepare a calibration curve by plotting the counts/min against the concentration of vitamin B in that standard. The B concentrations in the samples and internal standards are read from this caiibration curve. 

Sample preparation Serum (blood) 1 mL sample, add internal standard (e.g. 

Standardization—External standards, standard additions, and internal standards are a common feature of many quantitative analyses. Suggested experiments using these standardization methods are found in later chapters. A good project experiment for introducing external standardization, standard additions, and the importance of the sample s matrix is to explore the effect of pH on the quantitative analysis of an acid-base indicator. Using bromothymol blue as an example, external standards can be prepared in a pH 9 buffer and used to analyze samples buffered to different pHs in the range of 6-10. Results can be compared with those obtained using a standard addition. 

A standard sample was prepared containing 10.0 ppm of an analyte and 15.0 ppm of an internal standard. Analysis of the sample gave signals for the analyte and internal standard of 0.155 and 0.233 (arbitrary units), respectively. Sufficient internal standard was added to a sample to make it 15.0 ppm in the internal standard. Analysis of the sample yielded signals for the analyte and internal standard of 0.274 and 0.198, respectively. Report the concentration of analyte in the sample. 

Samples of analyte are dissolved in a suitable solvent and placed on the IR card. After the solvent evaporates, the sample s spectrum is obtained. Because the thickness of the PE or PTEE film is not uniform, the primary use for IR cards has been for qualitative analysis. Zhao and Malinowski showed how a quantitative analysis for polystyrene could be performed by adding an internal standard of KSCN to the sample. Polystyrene was monitored at 1494 cm- and KSCN at 2064 cm-. Standard solutions were prepared by placing weighed portions of polystyrene in a 10-mL volumetric flask and diluting to volume with a solution of 10 g/L KSCN in... 

Samples and calibration standards are prepared for analysis using a 10-mL syringe. Add 10.00 mL of each sample and standard to separate 14-mL screw-cap vials containing 2.00 mL of pentane. Shake vigorously for 1 min to effect the separation. Wait 60 s for the phases to separate. Inject 3.0-pL aliquots of the pentane layer into a GC equipped with a 2-mm internal diameter, 2-m long glass column packed with a stationary phase of 10% squalane on a packing material of 80/100 mesh Chromosorb WAW. Operate the column at 67 °C and a flow rate of 25 mL/min. 

Precision The precision of a gas chromatographic analysis includes contributions from sampling, sample preparation, and the instrument. The relative standard deviation due to the gas chromatographic portion of the analysis is typically 1-5%, although it can be significantly higher. The principal limitations to precision are detector noise and the reproducibility of injection volumes. In quantitative work, the use of an internal standard compensates for any variability in injection volumes. 

Two experiments are described in this paper. In the first experiment students determine the %w/w orange oil in a prepared sample by analyzing for d-limonene using anisole as an internal standard. Separations are accomplished using... 

Internal methods of quality assessment should always be viewed with some level of skepticism because of the potential for bias in their execution and interpretation. For this reason, external methods of quality assessment also play an important role in quality assurance programs. One external method of quality assessment is the certification of a laboratory by a sponsoring agency. Certification is based on the successful analysis of a set of proficiency standards prepared by the sponsoring agency. For example, laboratories involved in environmental analyses may be required to analyze standard samples prepared by the Environmental Protection... 

Internal standards at a known concentration are added to the sample after its preparation but prior to analysis to check for GC retention-time accuracy and response stability. If the internal standard responses are in error by more than a factor of two, the analysis must be stopped and the initial calibration repeated. Only if all the criteria have been met can sample analysis begin. 

Continuing calibration for a Series Method is performed using calibration check compounds. Surrogate compounds are added to the matrix before sample preparation to evaluate recovery levels. To check GC retention times, internal standards are added to a sample after its preparation for analysis. 

Approved techniques for manual and mechanical sampling are often documented for various commodities handled in commerce by industiy groups. Examples are the International Standards Organization (ISO), British Standards Association (BSA), Japan Institute of Standards (JIS), American Society for Testing Materi s (ASTM), and the Fertihzer Institute. Sampling standards developed for use in specified industry applications frequently include instructions for labora-toiy work in sample preparation and analysis—steps (2) and (3) above. 

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

HR-ICP-MS EEEMENT-2 (Pinnigan MAT, Germany) equipped with a standard introduction system (quartz water-cooled spray chamber, concentric nebulizer, torch with 1.5 mm i.d. injector and nickel cones) was used for measurements. The following operating conditions were used RP power 1150 W, coolant gas flow rate 16 1 min k auxiliary gas flow rate 0.85 1 min nebulizer gas flow rate 1.2 1 min k Sample uptake rate was 0.8-1 ml min k Measurements were performed with low and middle resolutions. Rh was used as an internal standard. Por calibration working standard solutions were prepared by diluting the multielemental stock solutions CPMS (SPEX, USA) with water to concentration range from 5 ng to 5 p.g I k... 

GLC yield is based on thermal conductivity corrections reladve to an appropriate internal standard. Product identity was confirmed by comparison of F NMR, H NMR, IR, and/or mass spectra with those of authentic samples prepared by alternative routes when possible Yields are based on ylide Isolated yields are given m parentheses. 

Results The raw data consisted of peak height ratios of signal internal standard, see data files VALIDl.dat (primary validation m - 0 repeats at every concentration), VALID2.dat (between-day variability), and VALID3. dat (combination of a single-day calibration with several repeats at 35 and 350 [ng/mlj in preparation of placing QC-sample concentration near these values). Fig. 4.29 shows the results of the back-calculation for all three files, for both the lin/lin and the log/log evaluations. Fig. 4.30 shows the pooled data from file VALID2.dat. 

---