Instrumental detection limits

How do you distinguish between the instrument detection limit (IDL) and the method detection limit (MDL) ... 

This fusion method produces an acid-soluble glass bead which is dissolved in nitric acid. It avoids the use of hydrofluoric and perchloric acids. The disadvantages are the cost of platinum labware, and the large quantities of LiB02 used to produce the glass bead increase the total dissolved solids and may contribute to polyatomic species. Dilution to counter these effects may reduce the elements of interest below the instrumental detection limits. 

Headspace analysis (EPA 3810, 5021) also works well for analyzing volatile petroleum constituents in soil. In the test method, the soil is placed in a headspace vial and heated to drive out the volatiles from the sample into the headspace of the sample container. Salts can be added for more efficient release of the volatile compounds into the headspace. Similar to water headspace analysis, the soil headspace technique is useful when heavy oils and high analyte concentrations are present, which can severely contaminate purge-and-trap instrumentation. Detection limits are generally higher for headspace analysis than for purge-and-trap analysis. 

The method detection limit (MDL) is the smallest quantity or concentration of a substance that a particular instrument can measure (Patnaik, 2004). It is related to the instrument detection limit (IDL), which depends on the type of instrument and its sensitivity, and on the physical and chemical properties of the test substance. 

The method detection limit is, in reality, a statistical concept that is applicable only in trace analysis of certain types of substances, such as organic pollutants by gas chromatographic methods. The method detection limit measures the minimum detection limit of the method and involves all analytical steps, including sample extraction, concentration, and determination by an analytical instrument. Unlike the instrument detection limit, the method detection limit is not confined only to the detection limit of the instrument. 

Interference free detection limits" and "Instrument detection limits", for example, do not specify the measuremerit capabilities of a complex measurement process including sample preparation... 

Based on 8-h daylight samples unless otherwise specified. h Generally below instrument detection limit. 

Determination of the instrumental detection limit of atomic absorption spectrometry and also precision as a function of concentration for the four elements listed. 

Table V. Instrumental Detection Limits Based on Twice the Standard Deviation of the Blank...

A low flow rate of mobile phase minimises the dispersion of compounds, which occurs inevitably throughout the instrument. Detection limits are also improved. The laminar flow within the column follows Poiseuille s law, the velocity of the mobile phase being at its maximum in the centre of the tube and zero at the wall. 

The instrument detection limit is obtained by replicate measurements (n > 7) of aliquots from one sample. The method detection limit, which is greater than the instrument detection limit, is obtained by preparing n > 7 individual samples and analyzing each one once. 

What is the difference between an instrument detection limit and a method detection limit What is the difference between robustness and ruggedness ... 

XRF analyses of Silver Lake and Sycan Marsh obsidian source samples suggested the possibility that the two sources could be differentiated based on small differences in strontium concentrations. However, when the standard error for strontium was taken into account, both groups overlapped at one standard deviation. Because of higher instrumental detection limits for strontium, NAA could not discriminate between the two sources. LA-ICP-MS analyses were conducted to determine if the sensitivity and precision of this analytical technique was sufficient to confirm the existence of the two compositional... 

Because of this great flexibility in the design, fabrication, and readout, cantilever arrays for gaseous (Kim et al., 2001) and biosensing aqueous applications (Arntz et al., 2003) have been realized. Needless to say, the issues of selectivity, dynamic range, response time, and so on depend ultimately on the interactions of the analyte with the selective layer. What cantilevers can offer is a low instrumental detection limit and the possibility of avoiding experimental artifacts due to the effects not related to the chemical interactions. Because they are relatively new, it is too early to estimate their usefulness. They will have to stand the test of time. 

Note that f-statistics should be followed when the sample size is small, i.e., <30. In the MDL measurements, the number of replicate analyses are well below 30, generally 7. For example, if the number of replicate analyses are 7, then the degrees of freedom, i.e., the ( -1) is 6, and, therefore, the t value for 6 should be used in the above calculation. MDL must be determined at the 99% confidence level. When analyses are performed by GC or GC/MS methods, the concentrations of the analytes to be spiked into the seven aliquots of the reagent grade water for the MDL determination should be either at the levels of their IDL (instrument detection limit) or five times the background noise levels (the noise backgrounds) at or near their respective retention times. 

Table 4.4 compares the sensitivities of various elemental analysis techniques based on instrument detection limits (IDLs). 

Table 4.4 Comparison of instrument detection limits for various elemental analysis...

IATA ICAP ICP ICP-AES ICP-MS ICV ID IDL IDW ISO International Air Transportation Association inductively coupled argon plasma inductively coupled plasma inductively coupled plasma-atomic emission spectrometry inductively coupled plasma-mass spectrometry initial calibration verification identification instrument detection limit investigation-derived waste International Standardization Organization... 

The ICP was a Perkin-Elmer 3000DV with an AS90 Autosampler, which has an instrument detection limit of about 1 ppb (for most elements) with a linear calibration up to 100 ppm (for most elements). Solid samples were prepared via microwave digestion in concentrated nitric and hydrochloric acids, then diluted to volume. The ICP was calibrated and verified with two independent, certified standard sets. Spikes and dilutions were done for each batch of samples to check for and/or mitigate any matrix effects. The ICP process ran a constant pump rate of 1.5 mL/min for all samples and standards during analysis. A 3 mL/min rinse and initial sample flush were used to switch between each sample and standard. The plasma was run at 1450 W with argon flow. Trace metal-grade (sub-ppb) acids and two independently NIST-certified calibration standard sets were used for calibration and method verification. 

The concentration of analytes that can be measured in various materials has been decreasing over the years as sensitivity and detection limits of analytical techniques have improved. The method detection limit (MDL) is the order of magnitude of the smallest quantity or concentration of substance which can be detected in principle the limit of detection (LOD), on the contrary, is a precisely calculable statistical value for a particular, defined analytical procedure. The instrument detection limit (IDL) is the smallest signal above background noise that an instrument can detect reliably. It is expressed either as an absolute limit (in units of mass, eg, ng), or as a relative limit (in terms of concentration, eg, g mL 1). 

Standard Curve Inject each calibration standard in triplicate. Normal instrument linearity extends to 25 ng/mL. If nonlinear calibration capability is not available, limit the working calibration curve to <25 ng/mL. Use the calibration algorithms provided in the instrument software. Recheck calibration periodically (<15 samples) by running a 25- or 50-ng/ mL calibration standard interspersed with samples. If recheck differs from calibration by >10%, recalibrate the instrument. The instrumental detection limit (DL) and quantitation limit (QL), in picograms, may be based on 7 to 10 replicates of the Sample Preparation Blank and calculated as follows ... 

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