Drugs calibration curves

The calibration sensitivity of the analytical method employed is simply determined as the slope of the calibration curve. For example, in the case of methyl paraben, the value of calibration sensitivity obtained was 1.6 mAl I/min///M (Figure 6.22). Analytical sensitivity is defined as the ratio between calibration sensitivity and the value of the standard deviation obtained at each concentration.10 The value of the standard deviation encountered for a concentration of 0.6 //M was 0.1, resulting in an analytical sensitivity for methyl paraben at 0.6 //M of 16 m. II/min///M. As indicated for LOD and LOQ, the values obtained for linearity and sensitivity depend on the analytes employed and the corresponding method and instrumental parameters. For example, Liu et al.9 evaluated the LOD and LOQ for Drug A (released from OROS) for a particular analytical method employing //Pl.C to be 0.5 //g/ml. and 2.0 //g/mL, respectively. 

SSL stability size distribution, level of free drug, and ApH remain unaltered for more than six months storage at 4°C ApH for both % MA and % AO are based on calibration curves. 

NIR calibration curves were prepared by measuring the key compact attributes on rectangular surrogate tablets, prepared on the laboratory Carver press. The preparation of the calibration curve requires samples with attributes spanning the range of values likely to be encountered during roller compaction. Hence, drug content (for content uniformity), relative humidity... 

External Standard. In this approach, related substance levels are determined by calculation using a standard curve. The concentration of related substance is determined by the response (i.e., peak area of individual related substance) and the calibration curve. A reference standard of the drug substance is typically used in the calibration. Therefore, a response factor correction may be required if the response of related substance is very different from that of the drug substance. A single-point standard curve (Figure 3.4) is appropriate when there is no significant v-intercept. Otherwise, a multipoint calibration curve (Figure 3.5) has to be used. Different types of calibration are discussed in Section 3.2.3. 

Reduced Linear Range. Unlike the area percent and high-low methods, which use the response of the drug substance in sample injections for calculation, an external standard method uses a standard curve. Typically, the concentration range of the calibration curve is similar to that of related substances in the sample (e.g., 1 to 5% of the nominal sample concentration). Therefore, this method requires a small linear range. 

As a summary of observations on sample preparation of all types, some generalizations can be reiterated. Whenever possible, blank samples spiked with standards should be employed and recovery studies should include assays of each extract, to monitor possible drug-substrate interaction. One technique effective in this regard, is to examine the aqueous phase by TLC after all the "free" drug has been extracted. Standard calibration curves should be compared to similar plots in the presence of sample matrix constituents whenever possible. GC should never be employed as the sole criterion in any analytical evaluation. 

Figure 7. Calibration curves for drugs showi in Figure 6.

The MALDI triple-quadrupole mass spectrometer generates calibration curves with linearity and dynamic ranges similar to those typically expected from a triple-quadrupole mass spectrometer. In most cases, linearity is established over three orders of magnitude with suitable accuracy and precision. Figure 11.5 depicts calibration curves obtained for some common drugs using neat standards. 

To run a patient sample, you will need to go through exactly the same deproteination, SFE cartridge extraction, IS addition, mobile phases dilution, and injection steps (Fig. 12.4f). From the peak heights relative to the IS height, we can now quantitate the amount of each drug in the patient s blood. To insure linearity, you may need to dilute our windowed plasma blank and spike it with different levels of each standard and plot calibration curves for each compound, but basically, our methods development is done. 

The absorbance measured with a base line at 3300 cm-l or 3 70 cm-l. The calibration curves were linear in the concentration range between 0-5 to 2 mg/ml and the results were in good agreement with those determined colorimetrically. The determination was not interferred with the coexistance of a limited amount of 1 0 possible drug constituents e.g., phenacetin and pyrabital (1 1 ). 

When matrix effect exists, it is usually preferable to coeluate the analyte and its internal standard to better reduce the impact of matrix effect on quantitation. The more their chromatographic peaks overlap, the better the correction is. Since the concentration of the analyte varies while the amount of IS added is constant, a choice must be made as to match which part of a calibration curve. Usually, the segment between 1/3 and 1/2 of the ULOQ is most important because this segment is expected to cover the average Cma for most drugs and metabolites. This is probably why other researchers have proposed to use IS concentrations around 1/3 or 1/2 of the ULOQ of an analyte. 

Shinozuka et al. [91] developed a sensitive method for the determination of four anthranilic acid derivatives (diclofenac sodium, aluminium flufenamate, mefenamic and tolfenamic acids) by HPLC procedure. The four drugs were converted into methylphthalimide (MPI) derivatives in a constant yield by reaction with /V-chloromethylphthalimide at 60°C for 30 min. The production of the MPI derivatives were confirmed by mass spectrometry. The MPI derivatives of the four drugs were separated by HPLC using a C-18 bonded phase LiChrospher RP-18 column (250 x 4 mm i.d.) with acetonitrile-water (80 20, v/v) as mobile phase. The flow rate was 0.8 mL/min. The UV absorbance was measured at 282 nm. The calibration curves of the MPI derivatives of the drugs were linear from 1.0 to 5.0 pg/rnL. The detection limits of the four drugs were 0.5-5 ng. The extraction procedure for the four anthranilic acid derivatives added in the plasma and urine was performed by using Extrelut 1 column. Yields of column extraction of 100 pL of plasma and urine samples (containing 0.5 pg of anthranilic acid derivatives) with 6 mL of ethyl acetate were 84-106%. 

The concentration of the free drug (cu) in the ultrafiltrates or the concentration of bound fraction (Cb) in the retentate can be quantified by LC-MS/MS by means of a calibration curve. If radiolabeled substrate has been applied, liquid scintillation counting can be employed. 

In order to obtain calibration curves for other ratios of parent drug and metabolites, the ratio can be modified as well. In many cases, all analytes are used in equimolar ratios in order to obtain the same calibration range for all of the analytes. However, the assay calibration procedure has to cover the whole calibration range that is going to be used for each and every analyte. 

Moreover, there is no consensus about the definition of sensitivity limits (Tables 1.1 to 1.3) some authors indicate limits of detection (LOD), others claim only the limits of their calibration curves (lowest point of calibration curve [LPC]) or the lowest values detected (LDV), some refer to mg hair, others to mL of their extract. However, sensitivity is usually in the range of ng drug/mg hair. Some scientists even claim detection limits in the pg range (morphine and 6-monoacetylmorphine cocaine and benzoylecgonine nicotine, and cotinine, and... 

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